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1.
Biochem J ; 360(Pt 3): 609-15, 2001 Dec 15.
Article in English | MEDLINE | ID: mdl-11736650

ABSTRACT

Sex hormone-binding globulin (SHBG) is the main carrier for androgens and oestrogens in humans. It mediates the transport of steroid hormones in the circulation and testicular fluid, and regulates their bioavailability to steroid-responsive tissues. In addition, the protein interacts with membrane receptors expressed in target tissues. Binding to the receptors is suspected to facilitate the uptake of steroid hormones and/or elicit cellular signal transduction. The identity of the SHBG receptor has not yet been resolved, in part due to a lack of sufficient quantities of authentic SHBG for receptor purification and molecular characterization. We have successfully addressed this problem by establishing an episomal expression system in human embryonic kidney cells that produces 5 mg of fully active human SHBG per litre. The recombinant protein resembles native SHBG in terms of structure, glycosylation pattern and steroid-binding activity. Moreover, the protein interacts with plasma membranes in steroid target tissues, an activity not observed with SHBG from other recombinant expression systems. Thus our studies have removed an important obstacle to the further elucidation of the role SHBG plays in steroid hormone action.


Subject(s)
Estradiol/metabolism , Hydrocortisone/metabolism , Sex Hormone-Binding Globulin/genetics , Cell Line , Cell Membrane/metabolism , Circular Dichroism , Cloning, Molecular , DNA Primers , Electrophoresis, Polyacrylamide Gel , Endometrium/metabolism , Epididymis/metabolism , Female , Glycosylation , Humans , Kidney , Kinetics , Male , Polymerase Chain Reaction , Protein Binding , Protein Conformation , Recombinant Proteins/chemistry , Recombinant Proteins/metabolism , Sex Hormone-Binding Globulin/metabolism , Testosterone/metabolism
2.
J Mol Biol ; 314(2): 293-309, 2001 Nov 23.
Article in English | MEDLINE | ID: mdl-11718562

ABSTRACT

The monoclonal antibody tAb2 binds the N-terminal sequence of transforming growth factor alpha, VVSHFND. With the help of combinatorial peptide libraries it is possible to find homologous peptides that bind tAb2 with an affinity similar to that of the epitope. The conformational flexibility of short peptides can be constrained by cyclization in order to improve their affinity to the antibody and their stability towards proteolysis. Two cyclic peptides which are cross-reactive binders for tAb2 were selected earlier using combinatorial peptide libraries. One is cyclized by an amide bond between the N-alpha group and the side-chain of the last residue (cyclo-SHFNEYE), and the other by a disulfide bridge (cyclo-CSHFNDYC). The complex structures of tAb2 with the linear epitope peptide VVSHFND and with cyclo-SHFNEYE were determined by X-ray diffraction. Both peptides show a similar conformation and binding pattern in the complex. The linear peptide SHFNEYE does not bind tAb2, but cyclo-SHFNEYE is stabilized in a loop conformation suitable for binding. Hence the cyclization counteracts the exchange of aspartate in the epitope sequence to glutamate. Isothermal titration calorimetry was used to characterize the binding energetics of tAb2 with the two cyclic peptides and the epitope peptide. The binding reactions are enthalpically driven with an unfavorable entropic contribution under all measured conditions. The association reactions are characterized by negative DeltaC(p) changes and by the uptake of one proton per binding site. A putative candidate for proton uptake during binding is the histidine residue in each of the peptides. Hydrogen bonds and the putative formation of an electrostatic pair between the protonated histidine and a carboxy group may contribute markedly to the favorable enthalpy of complex formation. Implications to cyclization of peptides for stabilization are discussed.


Subject(s)
Antibodies, Monoclonal/immunology , Cross Reactions/immunology , Immunoglobulin Fab Fragments/immunology , Peptides, Cyclic/chemistry , Peptides, Cyclic/immunology , Transforming Growth Factor alpha/immunology , Amino Acid Sequence , Animals , Antibodies, Monoclonal/chemistry , Antibody Affinity , Base Sequence , Binding Sites, Antibody , Calorimetry , Complementarity Determining Regions/chemistry , Complementarity Determining Regions/immunology , Crystallography, X-Ray , Entropy , Epitopes/chemistry , Epitopes/immunology , Histidine/chemistry , Histidine/metabolism , Hydrogen Bonding , Immunoglobulin Fab Fragments/chemistry , Immunoglobulin Heavy Chains/chemistry , Immunoglobulin Heavy Chains/immunology , Immunoglobulin kappa-Chains/chemistry , Immunoglobulin kappa-Chains/immunology , Mice , Models, Molecular , Molecular Sequence Data , Protein Conformation , Static Electricity , Transforming Growth Factor alpha/chemistry , Water/chemistry , Water/metabolism
3.
FEBS Lett ; 505(3): 436-40, 2001 Sep 21.
Article in English | MEDLINE | ID: mdl-11576543

ABSTRACT

At the transcriptional level, the pSM19035-encoded omega protein coordinates the expression of proteins required for control of copy number and maintenance of plasmids. Using circular dichroism, fluorescence spectroscopy, ultracentrifugation and an electrophoretic mobility shift assay, the wild-type omega protein and a variant with a C-terminal hexa-histidine tag (omega-H(6)) were characterized. The omega protein is mainly alpha-helical (42%), occurs as homodimer in solution, unfolds thermally with half transition temperatures, T(m), between approximately 43 and approximately 78 degrees C depending on the ionic strength of the buffer, and binds PcopS-DNA with high affinity. The omega-H(6) protein has a modified conformation with lower alpha-helix content (29%), lower thermal stability, and strongly reduced affinity to PcopS-DNA.


Subject(s)
Bacterial Proteins/metabolism , DNA-Binding Proteins/metabolism , Plasmids , Streptococcus pyogenes/genetics , Bacterial Proteins/chemistry , Bacterial Proteins/genetics , Bacterial Proteins/isolation & purification , Circular Dichroism , DNA-Binding Proteins/chemistry , DNA-Binding Proteins/genetics , DNA-Binding Proteins/isolation & purification , Dimerization , Protein Denaturation , Spectrometry, Fluorescence , Thermodynamics , Ultracentrifugation
4.
J Mol Recognit ; 14(2): 89-98, 2001.
Article in English | MEDLINE | ID: mdl-11301479

ABSTRACT

The mechanism of recognition of proteins and peptides by antibodies and the factors determining binding affinity and specificity are mediated by essentially the same features. However, additional effects of the usually unfolded and flexible solution structure of peptide ligands have to be considered. In an earlier study we designed and optimized six peptides (pepI to pepVI) mimicking the discontinuous binding site of interleukin-10 for the anti-interleukin-10 monoclonal antibody (mab) CB/RS/1. Three of them were selected for analysis of their solution conformation by circular dichroism measurements. The peptides differ in the content of alpha-helices and in the inducibility of helical secondary structures by trifluoroethanol. These properties, however, do not correlate with the binding affinity. PepVI, a 32-mer cyclic epitope mimic, has the highest affinity to mab CB/RS/1 identified to date. CD difference spectroscopy suggests an increase of the alpha-helix content of pepVI with complex formation. Binding of pepVI to mab CB/RS/1 is characterized by a large negative, favorable binding enthalpy and a smaller unfavorable loss of entropy (DeltaH degrees = -16.4 kcal x mol(-1), TDeltaS degrees = -6.9 kcal x mol(-1)) resulting in DeltaG degrees = -9.5 kcal x mol(-1) at 25 degrees C as determined by isothermal titration calorimetry. Binding of pepVI is enthalpically driven over the entire temperature range studied (10-35 degrees C). Complex formation is not accompanied by proton uptake or release. A negative heat capacity change DeltaC(p) of -0.354 kcal x mol(-1) x K(-1) was determined from the temperature dependence of DeltaH degrees. The selection of protein mimics with the observed thermodynamic properties is promoted by the applied identification and iterative optimization procedure.


Subject(s)
Antigen-Antibody Reactions , Epitopes, B-Lymphocyte/immunology , Interleukin-10/immunology , Molecular Mimicry , Binding Sites, Antibody , Binding, Competitive/immunology , Calorimetry , Circular Dichroism , Molecular Mimicry/immunology , Peptide Library
5.
Protein Expr Purif ; 20(2): 314-23, 2000 Nov.
Article in English | MEDLINE | ID: mdl-11049755

ABSTRACT

Dynamin II, a large GTP-binding protein, is involved in endocytosis and in vesicle formation at the trans-Golgi network. To further elucidate functions of dynamin II, the pleckstrin homology domain (PHD), the proline-rich domain (PRD), and the C-terminal part of dynamin II (dynamin(500-870)) were expressed in Escherichia coli. The PHD, tagged C-terminally by a (His)(6) peptide, was expressed to 15% of cellular proteins and could be purified on nickel-chelating agarose. On the contrary, the PRD and dynamin(500-870) had to be tagged with a (His)(6) peptide at the N-terminus to bind to nickel-chelating agarose. Additional tagging with the S-peptide, which forms a stable complex with immobilized S-protein, allowed removal of strongly interacting E. coli proteins. Circular dichroic spectra indicate a structured recombinant PHD with a secondary structure content similar to that of the known PHD from dynamin I. The N-terminally tagged, recombinant PRD is unfolded but nevertheless binds specifically to the SH3 domain of amphiphysin II as well as to proteins extracted from rat brain. The described methods are suitable to isolate functionally active domains of dynamin II in sufficient amount and purity for further studies.


Subject(s)
GTP Phosphohydrolases/isolation & purification , GTP Phosphohydrolases/metabolism , Amino Acid Sequence , Animals , Cell Membrane/metabolism , Chromatography, Affinity , Circular Dichroism , Dynamin I , Dynamins , Escherichia coli , GTP Phosphohydrolases/chemistry , GTP Phosphohydrolases/genetics , Molecular Sequence Data , Nerve Tissue Proteins/metabolism , Peptide Fragments/chemistry , Peptide Fragments/genetics , Peptide Fragments/isolation & purification , Peptide Fragments/metabolism , Protein Binding , Protein Folding , Protein Structure, Secondary , Protein Structure, Tertiary , Rats , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/isolation & purification , Recombinant Fusion Proteins/metabolism , Sequence Homology, Amino Acid , Spectrometry, Fluorescence , Structure-Activity Relationship , src Homology Domains
6.
J Biol Chem ; 275(4): 2447-54, 2000 Jan 28.
Article in English | MEDLINE | ID: mdl-10644698

ABSTRACT

Previous protein unfolding studies had suggested that IF2 C, the 24. 5-kDa fMet-tRNA binding domain of Bacillus stearothermophilus translation initiation factor IF2, may consist of two subdomains. In the present work, the four Phe residues of IF2 C (positions 531, 599, 657, and 721) were replaced with Trp, yielding four variant proteins having intrinsic fluorescence markers in different positions of the molecule. Comparison of the circular dichroism and Trp fluorescence changes induced by increasing concentrations of guanidine hydrochloride demonstrated that IF2 C indeed consists of two subdomains: the more stable N-terminal (IF2 C-1) subdomain containing Trp-599, and the less stable C-terminal (IF2 C-2) subdomain containing Trp-721. Isolated subdomain IF2 C-2, which consists of just 110 amino acids (from Glu-632 to Ala-741), was found to bind fMet-tRNA with the same specificity and affinity as native IF2 or IF2 C-domain. Trimming IF2 C-2 from both N and C termini demonstrated that the minimal fragment still capable of fMet-binding consists of 90 amino acids. IF2 C-2 was further characterized by circular dichroism; by urea-, guanidine hydrochloride-, and temperature-induced unfolding; and by differential scanning calorimetry. The results indicate that IF2 C-2 is a globular molecule containing predominantly beta structures (25% antiparallel and 8% parallel beta strands) and turns (19%) whose structural properties are not grossly affected by the presence or absence of the N-terminal subdomain IF2 C-1.


Subject(s)
Peptide Initiation Factors/metabolism , RNA, Transfer, Met/metabolism , Amino Acid Sequence , Base Sequence , Binding Sites , Calorimetry, Differential Scanning , DNA Primers , Guanidine , Hot Temperature , Peptide Initiation Factors/chemistry , Peptide Initiation Factors/genetics , Prokaryotic Initiation Factor-2 , Protein Denaturation , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Spectrometry, Fluorescence
7.
FEBS Lett ; 459(3): 332-6, 1999 Oct 15.
Article in English | MEDLINE | ID: mdl-10526160

ABSTRACT

Mutations of the cysteines (positions 668 and 714) were generated in the IF2 C domain of Bacillus stearothermophilus translation initiation factor IF2. The corresponding proteins were characterized functionally and structurally. Most (yet not all) amino acid replacements at both positions resulted in severe reduction of the fMet-tRNA binding activity of IF2 C without grossly altering its structure. Our work demonstrates that: (a) both Cys residues are buried within an hydrophobic core and not accessible to protonation or chemical substitution, (b) neither Cys is functionally essential and (c) both Cys residues are located near the active site, probably without participating directly in fMet-tRNA binding.


Subject(s)
Cysteine/metabolism , Geobacillus stearothermophilus/metabolism , Peptide Initiation Factors/metabolism , RNA, Transfer, Met/metabolism , Binding Sites , Cysteine/genetics , Geobacillus stearothermophilus/genetics , Guanidine/metabolism , Mutagenesis, Site-Directed , Peptide Initiation Factors/chemistry , Peptide Initiation Factors/genetics , Prokaryotic Initiation Factor-2 , Protein Conformation , Protein Denaturation , Spectrum Analysis, Raman
8.
Biochim Biophys Acta ; 1431(1): 120-31, 1999 Apr 12.
Article in English | MEDLINE | ID: mdl-10209285

ABSTRACT

Conformation, acid-induced conformational changes and stability of the murine monoclonal antibody CB4-1 directed against the human immunodeficiency virus type 1 capsid protein p24, and its Fab and Fc fragments, were analysed by circular dichroism (CD), fluorescence, and differential scanning calorimetry (DSC) measurements. CD spectra show the characteristics expected for beta-proteins. Lowering the pH to 3.5 reduces the stability, but does not change the conformation. Between pH 3.5 and 2.0 conformational changes and the formation of new structures are indicated. Deconvolution of the bimodal DSC curves of CB4-1 reveals five 'two-state' transitions at pH 7.5. At pH 5 and below, only four transitions are found. Half transition temperatures Tm and molar enthalpy changes DeltaHm gradually decrease at pH 4 and 3.4. At pH 2.1, two low-temperature (Tm=36.9 and 44.1 degrees C) and two high-temperature (Tm=74.6 and 76.8 degrees C) transitions are identified. The Fab and Fc fragments behave similarly. Deconvolution of their monophasic DSC curves yields two 'two-state' transitions for each fragment. Tm and DeltaHm values gradually decrease at pH 4.0 and 3.4; and at pH 2.1 and 2.8 for Fab and Fc, respectively, one of the transitions is found at high temperature (Tm=67.2 and 75.9 degrees C for Fab and Fc, respectively).


Subject(s)
Antibodies, Monoclonal/chemistry , HIV Core Protein p24/immunology , HIV-1 , Hot Temperature , Protein Folding , Calorimetry, Differential Scanning , Circular Dichroism , Hydrogen-Ion Concentration , Immunoglobulin Fab Fragments/chemistry , Immunoglobulin Fc Fragments/chemistry , Immunoglobulin G/chemistry , Protein Conformation , Spectrometry, Fluorescence
9.
Nat Biotechnol ; 17(3): 271-5, 1999 Mar.
Article in English | MEDLINE | ID: mdl-10096295

ABSTRACT

We synthetically reconstructed a discontinuous binding site on interleukin-10 (IL-10) that recognizes the neutralizing anti-IL-10 antibody CB/RS/1. To design the 32-mer IL-10 mimic, a discontinuous interaction site on IL-10 was mapped, and binding studies with epitope-derived peptides led to specific replacement of several amino acids. Both parts of the interaction site were combined by addition of a linker molecule. Systematic analoging of the combined molecule then led to introduction of several additional substitutions in both regions and the linker. All possible disulfide bridge-containing variants of the 32-mer were tested by binding studies. Parallel syntheses were performed on continuous cellulose membranes by spot synthesis. As a result, a conformationally stabilized IL-10-derived molecule was obtained that both binds to and neutralizes the biological activity of CB/RS/1 in the low nanomolar range. This synthetic approach is a powerful alternative to phage display methods for the design of protein mimics.


Subject(s)
Binding Sites/physiology , Interleukin-10/chemistry , Amino Acid Substitution , Binding, Competitive , Dose-Response Relationship, Drug , Enzyme-Linked Immunosorbent Assay , Epitopes , Humans , Kinetics , Leukocytes, Mononuclear/metabolism , Lipopolysaccharides/metabolism , Peptide Biosynthesis , Peptide Mapping , Tumor Necrosis Factor-alpha/metabolism
10.
Virology ; 254(1): 6-10, 1999 Feb 01.
Article in English | MEDLINE | ID: mdl-9927569

ABSTRACT

Protein-protein interactions of the p24 (HIV-1) capsid protein play an essential role in the production of infectious virus particles. To map the putative p24 dimerization site, a set of overlapping peptides spanning the p24 sequence was prepared using spot synthesis on a cellulose membrane and probed with recombinant p24 (rp24). Three sequence regions interacting with rp24 were identified. Peptides from each region were synthesized, but only one peptide was effectively able to inhibit rp24 dimerization in solution. Amino acids that were exposed in the corresponding p24 region were mutated in rp24, resulting in a significant decrease of rp24 dimerization. Thus, participation of this region in virus capsid assembly can be assumed.


Subject(s)
HIV Core Protein p24/metabolism , Peptides/metabolism , Animals , Binding Sites , Dimerization , Humans , Mice
11.
Eur J Biochem ; 257(1): 101-11, 1998 Oct 01.
Article in English | MEDLINE | ID: mdl-9799108

ABSTRACT

A gene (lamR) encoding laminarinase (LamR) was cloned from the marine thermophilic eubacterium Rhodothermus marinus ITI278. The enzyme purified from recombinant Escherichia coli cells hydrolyses mixed 1,3-1,4-beta-glucans (lichenan, barley and oat beta-glucan) and 1,3-beta-homoglucans (laminarin, curdlan) by an endo type action pattern. The CD spectrum of laminarinase is characteristic for a protein with prevailing beta secondary-structural elements, and the fluorescence spectrum points to a surface localisation of the tryptophan residues. A half-transition concentration of 5.4 M guanidinium chloride was measured for the denaturant-induced unfolding of laminarinase monitoring changes of the ellipticity at 222 nm and the fluorescence. Substitution of acidic residues Glu129, Asp131 and Gln134, which are invariant in family 16 glycosyl hydrolases, caused a severe reduction of beta-glucan-hydrolysing activity suggesting their central role in enzymatic hydrolysis. Deletion of Met133 drastically reduced catalytic activity. Met133 is invariant in family 16 laminarinases but not present in the active-site region of bacterial 1,3-1,4-beta-glucanases which also belong to glycosyl hydrolase family 16. Replacement of Met133 by Ala, Cys or Trp did not affect activity against 1,3-1,4-beta-polyglucans and 1,3-beta-polyglucans, but in mutant Met133A the rate of hydrolysis of cellobiosyltriose (G1-4G1-3Gr) was increased about 10 times. Hydrolysis of 1,3-beta-oligosaccharides and 1,4-beta-oligosaccharides (DP 2-7) demonstrated the ability of the enzyme to cleave 1,3-beta-linkages and 1,4-beta-linkages in low-molecular-mass carbohydrates independent of the structure of neighbouring linkages. The laminarinase contains five or six subsites for substrate binding according to the action pattern deduced from hydrolysis of labelled and unlabelled curdlan oligosaccharides of different chain length.


Subject(s)
Glucan Endo-1,3-beta-D-Glucosidase/chemistry , Gram-Negative Aerobic Bacteria/enzymology , Amino Acid Sequence , Base Sequence , Binding Sites , Circular Dichroism , Cloning, Molecular , DNA Primers , Enzyme Stability , Glucan Endo-1,3-beta-D-Glucosidase/genetics , Glucan Endo-1,3-beta-D-Glucosidase/metabolism , Guanidine , Hot Temperature , Molecular Sequence Data , Mutagenesis, Site-Directed , Protein Conformation , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Sequence Homology, Amino Acid , Spectrometry, Fluorescence , Substrate Specificity
12.
Biochemistry ; 36(26): 8107-13, 1997 Jul 01.
Article in English | MEDLINE | ID: mdl-9201959

ABSTRACT

The M and M-like proteins of Streptococcus pyogenes are fibrous cell surface proteins. They have multiple binding sites for several human proteins and are composed of the C-terminal anchor domain, the alpha-helical coiled-coil domain, and the N-terminal non-coiled-coil domain. The coiled-coil domain of the M1 protein consists of repeat units called B, C, and D and a spacer unit S between B and C. Recombinant fragments A-B-S-C-D, A-B-S, B-S-C, S-C, S-C-D, C-D, and C of the coiled-coil domain were studied by analyzing their secondary structures and binding affinities to human serum albumin (HSA). As shown by circular dichroism, all fragments are in an alpha-helical conformation. C-D and S-C-D form coiled coils at room temperature and bind below 37 degrees C with high affinity to HSA. C-D and S-C-D unfold in two steps with Tm values of approximately 31 and approximately 65 degrees C; complex formation with HSA increases the unfolding temperatures. B-S-C has a lower alpha-helical content, a less pronounced coiled-coil conformation, and a reduced thermal stability, binds HSA weaker, and is only slightly stabilized by HSA binding in comparison to C-D and S-C-D. C and S-C are less stable than the other fragments and are not organized as coiled coils showing some features of alpha-helical single strands only below 20 degrees C, and binding of HSA was not observed. The results indicate that the formation of coiled-coil structures, supported by flanking D regions and, to a lesser extent also B regions, is essential for the binding of C repeat units to HSA.


Subject(s)
Antigens, Bacterial , Bacterial Outer Membrane Proteins , Bacterial Proteins/chemistry , Bacterial Proteins/metabolism , Carrier Proteins/chemistry , Carrier Proteins/metabolism , Peptide Fragments/metabolism , Serum Albumin/metabolism , Chromatography, Gel , Circular Dichroism , Humans , Peptide Fragments/chemical synthesis , Peptide Fragments/chemistry , Protein Binding , Protein Conformation , Protein Structure, Secondary , Protein Structure, Tertiary , Repetitive Sequences, Nucleic Acid , Serum Albumin/pharmacology , Streptococcus pyogenes/metabolism , Temperature , Thermodynamics
13.
Biochemistry ; 36(11): 3170-8, 1997 Mar 18.
Article in English | MEDLINE | ID: mdl-9115993

ABSTRACT

Conformation and stability of the C-terminal domain of initiation factor IF2 from Bacillus stearothermophilus were analyzed by circular dichroism, fluorescence and Raman spectroscopy, and microcalorimetry under different solvent conditions. From circular dichroism and Raman measurements, IF2C at neutral pH can be classified as an alpha + beta protein. Solvent perturbation and Raman spectroscopy indicate a high accessibility of the tyrosine residues in the native protein. The Gdn/HCl-induced unfolding of IF2C was monitored by circular dichroism. IF2C unfolding at neutral pH proceeds in two discrete steps. The midpoints (c(m)) and the free energy of unfolding (deltaG(u)H2O) of the first and second transition are 2.05 M and 6.2 kcal x mol(-1) and 4.1 M and 12.9 kcal x mol(-1), respectively. ANS does not bind to the stable intermediate formed at 3 M Gdn/HCl. It seems likely that IF2C is composed of two subdomains which unfold in a stepwise process. Melting experiments at pH 7.0 are impaired by irreversible aggregation at higher temperatures. However, in Gdn/HCl containing buffer at denaturant concentrations up to 1.5 M the melting becomes a reversible process and can be analyzed by differential scanning calorimetry. At Gdn/HCl concentrations between 1.0 and 1.5 M, IF2C seems to be composed of two folding units with Tm values of about 60 and 78 degrees C and folding enthalpy values (deltaHm) of about 37 and 58 kcal x mol(-1). At pH values below pH 3.0, IF2C can adopt a new acid-induced conformation, which is characterized by a high secondary structure content and a strong ANS binding. The Gdn/HCl-induced unfolding of IF2C at pH 2.6 takes place only in one discrete step with a midpoint c(m) of 3.3 M and a deltaG(AUa)H2O of 11.9 kcal x mol(-1).


Subject(s)
Geobacillus stearothermophilus/metabolism , Peptide Initiation Factors/chemistry , Protein Structure, Secondary , Calorimetry , Circular Dichroism , Cloning, Molecular , Guanidine , Guanidines , Peptide Initiation Factors/biosynthesis , Peptide Initiation Factors/isolation & purification , Prokaryotic Initiation Factor-2 , Protein Denaturation , Protein Folding , Recombinant Proteins/biosynthesis , Recombinant Proteins/chemistry , Recombinant Proteins/isolation & purification , Solvents , Spectrometry, Fluorescence , Spectrum Analysis, Raman , Thermodynamics , Tyrosine
14.
Proteins ; 27(1): 26-35, 1997 Jan.
Article in English | MEDLINE | ID: mdl-9037709

ABSTRACT

Conformation and stability of three Sks from Streptococcus equisimilis strain H46A, Streptococcus pyogenes strain A374, and Streptococcus pyogenes strain AT27 were compared by limited proteolysis, CD, and fluorescence measurements and by DSC. The general similarity of the peptide CD spectra in the spectral region 185 to 260 nm indicates the same type of folding for the three proteins. Fluorescence and aromatic CD spectra are consistent with a predominant surface localization of the aromatic amino acids and a low rigidity of their surroundings. A major difference among the three Sks is shown by deconvolution of their excessive heat capacity functions. Deconvolution reveals two energetic folding units in Sk H46A but three energetic folding units in Sk A374 and Sk AT27. Digestion of the Sks with trypsin indicates a reduced sensitivity of the C-terminal region of Sk A374 and Sk AT27 in comparison to Sk H46A. This suggests that amino acids of the C-terminal region participate in the formation of the third folding unit of Sk A374 and Sk AT27.


Subject(s)
Streptococcus/enzymology , Streptokinase/chemistry , Amino Acid Sequence , Calorimetry, Differential Scanning , Circular Dichroism , Enzyme Stability , Hydrolysis , Molecular Sequence Data , Protein Structure, Secondary , Species Specificity , Spectrometry, Fluorescence , Streptokinase/metabolism , Trypsin/metabolism
15.
Protein Sci ; 5(11): 2255-65, 1996 Nov.
Article in English | MEDLINE | ID: mdl-8931144

ABSTRACT

Thermostability and unfolding behavior of the wild-type (1,3-1,4)-beta-glucanases from Bacillus macerans (MAC) and Bacillus amyloliquefaciens (AMY) and of two hybrid enzymes H(A12-M) delta F14 and H(A12-M) delta Y13F14A were studied by spectroscopic and microcalorimetric measurements. H(A12-M) delta F14 is constructed by the fusion of 12 N-terminal amino acids of AMY with amino acids 13-214 of MAC, and by deletion of F14. In H(A12-M) delta Y13F14A, the N-terminal region of MAC is exchanged against the AMY sequence, Y13 is deleted, and Phe 14 is exchanged against Ala. The sequence of the N-terminal loop region from Pro 9 to amino acid 16 (or 17) is very important for the properties of the enzymes and influences the effects of Ca2+ ions on the thermostability and unfolding behavior of the enzymes. The half transition temperatures T(m) are higher in the presence of Ca2+ than in Ca2+ free buffer. Furthermore, the unfolding mechanism is influenced by Ca2+. In Ca(2+)-free buffer, MAC, H(A12-M) delta F14 and H(A12-M) delta Y13F14A unfold in a single cooperative transition from the folded state to the unfolded state, whereas for AMY, a two-step unfolding was found. In the presence of Ca2+, the two-step unfolding of AMY is strengthened. Furthermore, for H(A12-M) delta F14, a two-step unfolding is induced by Ca2+. These data indicate a two-domain structure of AMY and H(A12-M) delta F14, in the presence of Ca2+. Thus, point mutations in a peripheral loop region are decisive for thermal stabilities and unfolding mechanisms of the studied glucanases in the presence of Ca2+.


Subject(s)
Bacillus/enzymology , Endo-1,3(4)-beta-Glucanase , Glycoside Hydrolases/chemistry , Calcium/chemistry , Calorimetry, Differential Scanning , Enzyme Stability , Glycoside Hydrolases/metabolism , Guanidine , Guanidines , Models, Molecular , Protein Denaturation , Protein Folding , Temperature , Thermodynamics
16.
Biochemistry ; 35(28): 9097-105, 1996 Jul 16.
Article in English | MEDLINE | ID: mdl-8703914

ABSTRACT

It was found that the affinity of a monoclonal antibody directed against a recombinantly expressed HIV-1 capsid protein p24 (rp24) strongly increased after chemical modification of the Iysine residues of rp24 with different amounts of maleic anhydride. The extent and the sites of modification were analyzed by MALDI-TOF mass spectrometry. Unmodified rp24 and the differently modified rp24 samples were tested for binding the murine monoclonal antibody CB4-1 which recognizes the epitope GATPQDLNTML comprising residues 46-56 of rp24. An increase in the number of modified lysine residues led to enhanced binding affinity of CB4-1. Most pronounced effects were observed after substitution of the first amino groups: an average number of three modified residues per protein molecule increases the binding affinity by a factor of 23, but the substitution of the remaining nine residues increases the binding affinity only by a factor of 11. Fully modified rp24 variant proteins were bound by CB4-1 with Kd values comparable to that of the peptide epitope. Conformation and stability of the unmodified rp24, highly (rp24F, 9 residues; rp24G, 11 residues) modified, and fully modified protein (rp24I, 11 lysine residues and N-terminus) were analyzed by circular dichroism (CD) and fluorescence spectroscopy under different solvent conditions. Little difference in conformation and unfolding behavior was observed between the unmodified and highly modified rp24, which differ drastically in the antibody binding behavior. The fully modified sample, however, displayed a significant decrease in alpha-helical content. Thus, the epitope seems to be hidden (cryptotope) in the unmodified rp24 in a low-affinity binding conformation and becomes displayed at low levels of chemical modification which obviously induce subtle structural changes prior to changes of the overall folding observable by spectroscopic means.


Subject(s)
Epitopes/immunology , HIV Antibodies/immunology , HIV Core Protein p24/chemistry , HIV Core Protein p24/immunology , Amino Acid Sequence , Anilino Naphthalenesulfonates , Antibodies, Monoclonal/immunology , Antibody Affinity , Circular Dichroism , Epitopes/chemistry , Guanidine , Guanidines , Humans , Hydrogen-Ion Concentration , Lysine/chemistry , Maleic Anhydrides/pharmacology , Molecular Sequence Data , Peptide Mapping , Protein Conformation , Protein Folding , Recombinant Proteins/chemistry , Recombinant Proteins/immunology , Recombinant Proteins/metabolism , Spectrometry, Fluorescence , Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization , Thermodynamics
17.
Biochim Biophys Acta ; 1250(1): 9-18, 1995 Jul 03.
Article in English | MEDLINE | ID: mdl-7612658

ABSTRACT

Conformation and stability of the recombinant protein HIV-1 rp24 were analyzed by circular dichroism, fluorescence spectroscopy and differential scanning calorimetry under different solvent conditions. From circular dichroism measurements, HIV-1 rp24 at pH 5.8 can be classified as an all alpha-helical protein. A fluorescence maximum of about 330 nm indicates a predominantly hydrophobic environment of the five tryptophan residues. The GdnHCl-induced unfolding curves monitored by CD and fluorescence are sigmoidal and single phasic and the midpoints of transitions are independent on the protein concentration. For the calculation of free energy of unfolding delta GuH2O a 'two-state' model was applied. The calculated values are between 18 and 24 kJ/mol and thus on the lower limit of the conformational stability of globular proteins. Melting experiments at pH 5.8 are impaired by a strong irreversible aggregation at higher temperatures. However, at pH 3.0 and in the presence of 0.1% (w/v) ocytl beta-glucopyranoside the melting curves show a large degree of reversibility with a Tm value of 38 degrees C and a molar enthalpy change delta Hm of 218 kJ/mol. At pH < 2.5 HIV-1 rp24 can adopt a new conformation which is characterized by a high alpha-helical content, a strongly decreased CD in the aromatic region, a red-shift of the fluorescence spectrum and a strong binding of ANS. These spectral features of the acid-induced conformational state are similar to those obtained for molten globule-like folding states. HIV-1 rp24 unfolds cooperatively at pH 2.0 in the concentration range of about 1.5-3.0 M GdnHCl. The calculated values delta GuH2O at pH 2.0 of about 12 kJ/mol are significantly decreased in comparison to the delta GuH2O values of the protein at pH 5.8.


Subject(s)
Capsid/chemistry , Gene Products, gag/chemistry , HIV-1/chemistry , Protein Conformation , Anilino Naphthalenesulfonates/chemistry , Calorimetry, Differential Scanning , Circular Dichroism , Hydrogen-Ion Concentration , Protein Folding , Recombinant Proteins/chemistry , Spectrometry, Fluorescence
18.
Eur J Biochem ; 229(3): 726-35, 1995 May 01.
Article in English | MEDLINE | ID: mdl-7758469

ABSTRACT

The three hybrid glucanases (1-12)AMY x MAC(13-214), (1-12)AMY x des-Tyr13MAC(14-214); (1-16)AMY x MAC(17-214) are composed of short N-terminal segments of 12 or 16 amino acid residues derived from the Bacillus amyloliquefaciens glucanase (AMY) and of residues 13-214, 14-214 and 17-214, respectively, derived from the Bacillus macerans enzyme (MAC). The three proteins have similar conformational features as shown by the similar characteristics of their CD spectra in the far- and near-ultraviolet region. A metal-ion-binding site was identified in the hybrid glucanase (1-16)AMY x MAC(17-214) by a crystal structure analysis [Keitel, T., Simon, O., Borriss, R. & Heinemann, U. (1993) Proc. Natl Acad. Sci. USA 90, 5287-5291]. Only minor conformational changes of the three hybrid glucanases were observed depending on the presence or absence of Ca2+ ions but for (1-16)AMY x MAC(17-214) and (1-12)AMY x des-Tyr13MAC(14-214) the occupation of this metal-binding site by a Ca2+ ion is connected with a large increase of the stability against thermal and chemical unfolding. Surprisingly, for (1-12)AMY x MAC(13-214), which differs from (1-12)AMY x des-Tyr13MAC(14-214) by only one additional amino acid in an N-terminal loop region, the effect of Ca2+ ions on the stability is small. The exchange of a few amino acid residues near the N-terminus of the B. macerans glucanase against amino acids found at comparable positions in the B. amyloliquefaciens glucanase seems to influence very strongly the strength of the Ca2+ binding site and concomitantly the stability of the hybrid glucanases.


Subject(s)
Bacillus/enzymology , Calcium/metabolism , Glycoside Hydrolases/chemistry , Protein Structure, Secondary , Amino Acid Sequence , Binding Sites , Circular Dichroism , Enzyme Stability , Glycoside Hydrolases/metabolism , Hot Temperature , Molecular Sequence Data , Peptide Fragments/metabolism , Protein Conformation , Spectrometry, Fluorescence , Thermodynamics
19.
J Biomol Struct Dyn ; 12(5): 1041-54, 1995 Apr.
Article in English | MEDLINE | ID: mdl-7626239

ABSTRACT

Conformation and stability of EcoSSB, a single-stranded DNA binding protein encoded by Escherichia coli, were analyzed by circular dichroism and fluorescence measurements. From CD measurements at pH 7.5, EcoSSB can be classified as a protein with high alpha-helix and beta-sheet content. The hydrophobicity of the environment of the tryptophan residues of the native protein is only marginally increased in comparison to the unfolded protein. The GdnHCl induced unfolding curves measured by CD and fluorescence are coincident and sigmoidal and show a monophasic transition. The stability of EcoSSB is concentration dependent and the unfolding behavior can be described as a two-state transition from the folded tetrameter to unfolded monomers. The mean values of free energy of dissociation and unfolding delta GH2O mu are between 173 and 177 kJ.mol-1 and the mean half concentration c1/2 of GdnHCl of the transition curves are about 1.5 M and 1.7 M for protein concentrations of 0.1 mg.ml-1 and 0.5 mg.ml-1, respectively.


Subject(s)
DNA-Binding Proteins/chemistry , Escherichia coli/chemistry , Protein Folding , Circular Dichroism , DNA-Binding Proteins/metabolism , Protein Denaturation , Protein Structure, Secondary , Spectrometry, Fluorescence , Thermodynamics
20.
Int J Biol Macromol ; 16(4): 187-94, 1994 Aug.
Article in English | MEDLINE | ID: mdl-7848966

ABSTRACT

The conformations and stabilities of two forms of human plasminogen, Glu1-plasminogen (Glu1-HPg, Glu1-Asn791) and Lys78-plasminogen (Lys78-HPg, Lys78-Asn791), and two enzymatically derived plasminogen fragments, miniplasminogen (mini-HPg, Val443-Asn791) and microplasminogen (micro-HPg, Lys531-Asn791) were analysed by circular dichroism and differential scanning calorimetry. The two plasminogen forms differ by the lack of 77 N-terminal amino acids in Lys78-HPg in comparison to Glu1-HPg. Mini-HPg is composed of kringle 5 and the protease domain of HPg whereas micro-HPg is built from the protease domain of HPg and a stretch of about 15 amino acids from kringle 5. Differential scanning calorimetric measurements of Glu1-HPg and Lys78-HPg reveal seven thermal transitions for both plasminogen forms. The results obtained for Lys78-HPg largely agree with recently published data (Novokhatny, V. V., Kudinov, S. A. and Privalov, P. L. J. Mol. Biol. 1984, 179, 215). Three thermal transitions corresponding to kringle 5 and to two subdomains of the C-terminal protease region were identified for mini-HPg. In micro-HPg, the two thermal transitions of the protease region were found but one of the protease subdomains was modified and its stability was much higher than in any of the other studied proteins. According to the microcalorimetric data obtained for mini-HPg and micro-HPg, transitions 5 and 6 of Glu1-HPg and Lys78-HPg were reassigned to kringle 5 and to a subdomain of the protease region, respectively, in contrast to literature data.(ABSTRACT TRUNCATED AT 250 WORDS)


Subject(s)
Peptide Fragments/chemistry , Plasminogen/chemistry , Calorimetry, Differential Scanning , Circular Dichroism , Enzyme Stability , Humans , Protein Conformation , Protein Folding , Protein Structure, Secondary
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