[[correlation between macro- and micro-stability C(H)2 domains of human IgG2 and their biological activity. II. Calculation of thermodynamic functions characterizing domains stability].

The thermodynamic parameters of the stabilization of the native structure C(H)2 domains of human myeloma immunoglobulin LOM and SIN second subclass and their firstly obtained hFc fragments were determined using the methods of scanning microcalorimenry. A decrease in the termal stability and energy stability of the native of these domains in the intact proteins correlated in the "phisiological" range of temperatures (20-37 degrees C), mainly, with entropy factor.

Role of cis- and trans-interactions in manifestations of amyloidogenic properties of variable domains of Bence-Jones proteins TIM and LUS.

Intact Bence-Jones proteins TIM and LUS under simulated physiological conditions (10 mM phosphate buffer, pH 7.0, 100 mM NaCl, 37°C) did not display amyloidogenic properties. However, their isolated variable domains exhibit these qualities in full measure. Therefore, both intact proteins and their variable domains were studied using a complex of physical methods (scanning microcalorimetry, analytical centrifugation, optics) that allowed us to assess the stability of their tertiary and quaternary structures. The experimentally obtained thermodynamic functions indicated that the stability of isolated variable domains of TIM and LUS was comparable to the stability of similar domains in amyloidogenic proteins described earlier. However, inside the whole protein their stability was comparable to the stability of VL domains of ordinary Bence-Jones proteins. The decreased stability of the isolated variable domains of TIM and LUS was shown to be due both to weak interactions between a pair of variable domains (trans-interaction) and to a natural lack of interaction with the constant domains (cis-interaction).

[Thermodynamic parameters of stabilization in a compact form of the Caf1(13-149) subunit from Yersinia pestis].

With a number of experimental methods (circular dichroism, viscosity, intrinsic fluorescence and fluorescence labelling) the conformational folding-unfolding transitions in a compact monomeric form of the Caf1(13-149) subunit were studied under the action of guanidine hydrochloride in the temperature range from 5 to 45 degrees C. It has been shown that transitions always occur between two major states (unfolded and compact). It has made it possible to determine all main thermodynamic functions that characterize the compact state of the Caf1(13-149) subunit: temperature stability T(m), the free energy of stabilization deltaG(st), enthalpy deltaH(tr) and heat capacity jump deltaC collapse of the structure. Data obtained have been confirmed by an independent experiment on melting of fluorescently labeled proteins.

[The internal cavities of pike alpha-parvalbumin probably contain water].

The kinetics of hydrogen exchange of pike a-parvalbumin was investigated using the method of infrared spectroscopy (sensitive to the amide hydrogen atoms in the peptide) and radioisotope method (sensitive to all labile hydrogen atoms). Ultraslow exchangeable hydrogen atoms were found to be substantially less in the first case than in the second one. Taking into account that the internal cavities in the parvalbumin are formed by hydrophobic amino acid residues, devoid of labile hydrogen atoms, it is possible to make the most appropriate assumption, namely, these cavities contain water molecules, hydrogen atoms of which are ultraslow exchangeable.

[Stabilization energy of the compact Caf1(13-149) subunit from Yersinia pestis].

It has been shown by a variety of methods (circular dichroism, viscosimetry, intrinsic fluorescence, and fluorescence of labels) that, as in the case of small globular proteins the folding-unfolding transition in the Caf1(13-149) subunit under the action of two denaturants (urea and 1,3-dimethylurea) occurs between two major states (unfolded and compact). However, the free energy of the compact structure is only 8/9-9/2 kJ/mol (similar values for single-domain small proteins are in the range of 21-63 kJ/mol).

[Hydration of the compact and extended forms of pFh fragments from IgG3 Kuc and Sur].

It has been shown using scanning microcalorimetry and densitometry that partial specific heat and specific partial volume of two pFh fragments of IgG3 increase during the decay of its tertiary structure, the secondary structure, the double poly-L-proline helix, being unchanged. This effect may be explained by a high degree of hydration, which increases on globule decompactization due to increased accessibility of peptide groups of the helix to solvent.

[The influence of interdomain interaction on the amyloidogenic properties Bence-Jones proteins].

Isolated constant domains from two Bence-Jones proteins VAD and BIR able to form amyloid fibrils, whereas only the first of them to keep specific ability of the intact protein. Studies of conformation and stability of these proteins by scanning microcalorimetry, circular dichroism, fluorescence and analytical centrifugation at physiological conditions (10 mM phosphate buffer, pH 7.0, 100 mM NaCl) showed that the stability of isolated pair of constant domains (C(L)-C(L)) VAD and BIR is reduced by compared with standard (nonamyloidogenic) Bence-Jones protein. However, in the intact protein BIR stability of his constant domains increases sharply, which correlated with the loss of the protein ability to form amyloid fibrils.

[The unusual thermodynamic properties of compact forms pFh fragments (hinge region) IgG3 Kuc and Sur].

pFh fragments from the hinge region of human IgG3 Kuc and Sur can fold into compact form, resulting the formation of proteins with secondary (super-secondary) structure, which is represented almost exclusively double poly-L-proline helix. It was demonstrated by several methods that the thermal denaturation of compact form pFh fragment (hinge region) IgG3 Kuc and Sur occurs in two stages. The "two-state" model described the disintegration of the compact structure with preservation of the secondary structure (double poly-L-proline helix). In the second stage melts itself helix consisting of four cooperative units, which are formed by the sections with a high content of proline residues. Poliproline conformation of secondary structure and large number of disulfide bonds is responsible for high specific enthalpy of denaturation and high thermal stability.

[A protein with missing information about its tertiary structure folds into the compact globular structure].

It has been shown by the methods of hydrodynamics (equilibrium ultracentrifugation, velocity sedimentation, intrinsic viscosity) that a fragment of the structural protein Cafl (Cafl 13.149) from the pili-like fibril Yersinia pestis is in the monomeric state and is capable of forming the compact ternary structure spontaneously, without the involvement of chaperone or other subunits. This happens despite the fact that some information about the ternary structure of this protein is provided in fibrils by the "sticky" segment Alal-Thr12 of the neighboring subunit. As previously shown, it is this segment of another molecule in the norm that is an important element of the ternary structure of the subunit itself since it interacts with the acceptor cleft and participates in the formation of the hydrophobic core.

[Thermodynamic and hydrodynamic study of Bence-Jones proteins].

Four Bence-Jones proteins were investigated by CD, fluorescence and analytical ultracentrifugation methods at physiological conditions (10 mM phosphate buffer, pH 7.0, 100 mM NaCl). A joint analysis of optical melting curves for proteins and their fragments were demonstrated that protein VAD has reduced stability of its constant half, which correlates with the ability of both intact protein and its constant, rather than variable part to form amyloid fibrils. Data are reported which support the viewpoint that the detected decrease in the stability is caused by abnormal interaction between a pair of constant domains C(L).

[Fibrillar part of C1q factor from the complement system has a great amount of bound water].

The mass of sC1q-CLR fragments from the fibrillar part of the C1q factor from the complement system was determined using high- and low-rate centrifugation. It is shown that this value is essentially higher than the value expected from the amino acid and hydrocarbon compositions. In addition, these fragments have an unusually high partial specific volume. These data support the earlier suggested model according to which the N-terminal part of the fibrillar structure contains an abnormal large amount of bound water.

Human immunoglobulin light chains lambda form amyloid fibrils and granular aggregates in solution.

Myeloma nephropathy is a disorder characterized by deposition of monoclonal immunoglobulin light chains in the kidneys. The chains deposited form either amyloid fibrils or granular (amorphous) aggregates. Distinct molecular mechanisms leading to the formation of different aggregate types in kidney of patients with multiple myeloma are poorly understood. Here we describe the self-association kinetics of human monoclonal immunoglobulin light chains lambda (GRY) isolated from urine of a patient with multiple myeloma. Under physiological conditions, the isolated light chain exists predominantly in a form of covalent dimer with apparent molecular mass of 50.1 kD. Spectral probe binding, analytical gel filtration, Western blot analysis, and electron microscopy indicate that GRY dimer aggregation occurs via two different pathways producing either amyloid fibrils or amorphous aggregates depending on microenvironment. Incubation of GRY (25 microM) for 4-14 days at 37 degrees C in phosphate buffered saline (PBS), pH 7.0, or in PBS containing urea (0.8 M), pH 6.5, leads to amyloid fibril formation. Under electron microscopy, the fibrils show unbranched thread-like structures, approximately 60-80 x 1000 A in size, which can bind thioflavin T and Congo Red. GRY maintained in acetate buffer, pH 3.5, forms granular aggregates. The structure of GRY oligomers formed during the early stage of amyloid fibril formation (1-4 days) has been examined by means of protein cross-linking with homobifunctional reagents. These oligomers are predominantly trimers and tetramers.

[Aggregation of C-reactive protein in solutions at acid pH]. / Agregatsiia C-reaktivnogo belka v rastvorakh pri kislom znachenii pH.

The hydrodynamic properties of the C-reactive protein (CRP) at different pH were studied using quasi-elastic light scattering, size-exclusion liquid chromatography, and nonreducing gel electrophoresis. It was shown that a CRP solution at pH 5.0-7.2 presents a polydisperse system the major component of which is the native pentameric CRP. At pH 4.0-4.5, CRP exists in two states having different hydrodynamic properties: the native pentameric form with a molecular mass of 120 kDa and with the hydrodynamic radius of 4.03 nm and high-molecular-weight aggregates with a wide range of their molecular weight distribution. The interaction of the C-reactive protein with monoclonal antibodies to it indicates that conformation-dependent surface epitopes of the protein lose the native structure at pH 5.0-5.5. The aggregation of CRP is an irreversible process, which begins in a narrow pH range of pH 5.0-4.5 and is not accompanied by the dissociation into subunits but is determined by intermolecular interactions of its quasi-native pentamers.

[Hydrodynamic parameters of native C-reactive protein molecule in a solution]. / Gidrodinamicheskie parametry molekuly nativnogo C-reaktivnogo belka v rastvore.

The hydrodynamic properties of the C-reactive protein in solution (pH 6.8) were studied using quasi-elastic light scattering and size-exclusion liquid chromatography. It was shown that the solution containing the C-reactive protein represents a polydisperse system. The values of the translation diffusion coefficient and the apparent molecular weight of the C-reactive protein in solution at pH 6.8 were determined. The values of the translation diffusion coefficient, molecular weight and the hydration radius obtained suggest that the native pentameric C-reactive protein is the major form of the protein in solution at pH 6.8.

[Effect of Ca2+ ions on hydrodynamic properties of pentamer and decamer of C-reactive protein in solution]. / Vliianie ionov Ca2+ na gidrodinamicheskie svoistva pentamera i dekamera C-reaktivnogo belka v rastvore.

The molecular mass and sedimentation coefficient of native C-reactive protein in solution were determined by analytical ultracentrifugation in the presence and absence of calcium ions. Pentameric C-reactive protein was shown to be the major macroscopic form of this protein in solution. The removal of calcium ions from solution caused decompaction of the protein accompanied by changes in its hydrodynamic parameters. The sedimentation coefficient s20(0), w of pentameric C-reactive protein in solution containing 2 mM--Ca2+ (6.6S) exceeded that for C-reactive protein in solution containing 2 mM EDTA (6.4S). Analysis of average molecular masses Mw and Mz obtained from sedimentation data demonstrated that the solution of highly purified protein was not homogeneous. As shown by intermolecular crosslinking, the solution also contained the 241-kDa decamer of C-reactive protein (9.5S) as a separate macroscopic form, whose share hardly reached 10% in the presence of 2 mM Ca2+ and increased after removal of calcium ions. The decamers were shown to result from intermolecular association of the pentamers.

[Domain structure of CAF1M protein from Yersinia pestis. Structure and the role of various domains]. / Izuchenie domennoi struktury CAF1M Yersinia pestis. Struktura i rol' otdel'nykh domenov.

The cooperative structure of Caf1M from Yersinia pestis was studied using scanning microcalorimetry, fluorescence, and limited proteolysis. It was shown that, in Caf1M-Hg (a derivative in which the disulfide bond is replaced by an S-Hg-S bond), the first to melt is the N-domain. Then the C-domain melts. After renaturation in a buffer with a low NaCl concentration, only the C-domain is in the native state, and it can be obtained by limited proteolysis. After renaturation in a buffer with a high NaCl concentration, only the N-domain is in the native state, and it can be obtained by limited proteolysis. Both domains have native structure; however, only the N-domain interacts with Cafl (natural substrate for Caf1M).

[Interaction between CH2 and CH3-domains of human immunoglobulin G1 in glycosylated and aglycosylated Fc-fragments]. / Vzaimodeistvie mezhdu CH2 i CH3-domenami immunoglobulina G1 cheloveka v glikozilirovannykh i aglikozilirovannykh Fc-fragmentakh.

Heat denaturation of glycosylated and aglycosylated human immunoglobulin G1 Fc fragments was investigated by differential scanning microcalorimetry. The enthalpy of the interaction between aglycosylated CH2 and CH3 domains is significantly reduced at 37 degrees C (but not at 0 degree C) as compared to the glycosylated form. The temperature dependence is consistent with the data on restricted proteolysis by trypsin.

[Effect of immunoglobulin G1 Pro 290 residue on structural and biological characteristics of its SH2 domain]. / Vliianie ostatka Pro290 v immunoglobuline G1 na strukturnye i biologicheskie svoistva ego CH2-domena.

Tryptic hydrolysis of only one of 11 studied Fc fragments of human myeloma immunoglobulins G1 (IgG1) provided an intact CH2 domain in a high yield (up to 40% as opposed to 2-3% for other IgG1s). The only structural difference of this domain was shown to be the substitution of Pro for Lys290. This decreased the capacity of the IgG1 Sem Fc fragment to interact with proteins of the complement system.