Expression, purification, and mass spectrometric analysis of 15N, 13C-labeled RGD-hirudin, expressed in Pichia pastoris, for NMR studies.

A novel recombinant hirudin, RGD-hirudin, inhibits the activity of thrombin and the aggregation of platelets. Here, we successfully expressed (15)N, (13)C-labeled RGD-hirudin in Pichia pastoris in a fermenter. The protein was subsequently purified to yield sufficient quantities for structural and functional studies. The purified protein was characterized by HPLC and MALDI-TOF mass spectroscopy. Analysis revealed that the protein was pure and uniformly labeled with (15)N and (13)C. A bioassay showed that the anti-thrombin activity and the anti-platelet aggregation ability of the labeled protein were the same as those of unlabeled RGD-hirudin. Multidimensional heteronuclear NMR spectroscopy has been used to determine almost complete backbone (15)N, (13)C and (1)H resonance assignments of the r-RGD-Hirudin. The (15)N-(1)H HSQC spectrum of uniformly (15)N, (13)C-labeled RGD-hirudin allowed successful assignment of the signals. Examples of the quality of the data are provided for the (15)N-(l)H correlation spectrum, and by selected planes of the CBCA(CO)NH, CBCANH, and HNCO experiments. These results provide a basis for further studies on the structure-function relationship of RGD-hirudin with thrombin and platelets.

Hydrophobic cavity in C-terminus is essential for hTNF-α trimer conformation.

A variety of tumour necrosis factor α (TNF-α) derivatives have been bioengineered to improve antitumour activity and reduce toxicity. The expression of TNF-α in Escherichia coli usually yields a mixture of homotrimers and monomers; however, only the trimer shows antitumour activity. TNF-αD10, a bioengineered hTNF-α derivative, demonstrated 10-fold higher cytotoxicity against tumour cells compared to hTNF-α, but the trimer to monomer ratio was 58:42. In the present study, we investigated the structural differences between the trimer and the monomer of TNF-αD10. We found that the chemical shifts of the C-terminal Trp(114) in the trimer were significantly different from those in the monomer and that the replacement of Trp(114) with different amino acids remarkably reduced the trimer production. Further analysis of the publicly available X-ray crystallographic data for trimeric and monomeric hTNF-α revealed that the conformation of the U-shaped region formed by the fragment Cys(101)-Trp(114) was different between the two forms: a hydrophilic cavity in the monomer and a hydrophobic cavity in the trimer. These findings suggested the potential approaches of molecular and structural modification for future improvement of hTNF-α trimer production.

Overproduction of 15N-labeled r-RGD-hirudin in pichia pastoris for NMR studies.

The novel recombinant hirudin, r-RGD-hirudin, inhibits thrombin and platelet aggregation. Here, we reported over-expression of (15)N-labeled r-RGD-hirudin by Pichia pastoris in minimal medium. After extensive optimization, the yield of active r-RGD-hirudin reached ≈600 mg/L when the yeast cells were culture in a fermenter. The purified (15)N-labeled r-RGD-hirudin retained full biological activity and was uniformly labeled. Heteronuclear NMR of the (15)N-labeled r-RGD-hirudin was performed for the first time, and all signals in the heteronuclear single quantum coherence (HSQC) spectrum were successfully assigned.

Preparation of zeolite ANA crystal from zeolite Y by in situ solid phase iso-structure transformation.

A new method has been explored to synthesize zeolite ANA crystals with regular icositetrahedron in aqueous media via transformation of zeolite Y under the conditions of low temperature, short reaction time, and without organic template. The products are perfect, almost 100% crystals. The samples prepared at different crystallization stages are measured by XRD, TEM, and SEM to investigate the transformation mechanism from zeolite Y to zeolite ANA. It has been demonstrated for the first time that the mechanism of forming a zeolite ANA polycrystal with sphere or shell morphologies is the in situ solid phase iso-structure transformation (Is-SPIST) of zeolite Y. The Is-SPIST mechanism is also supported by the results of steam-induced crystallization experiments and other assistant means, including the same Si/Al ratio, the same weight, the same particle size, and the same morphology before and after transformation of zeolite Y to zeolite ANA. It is also observed that a spherical or shell ANA polycrystal is constructed via the reconstruction from its exterior to interior, to form an ANA single crystal with a solid or hollow icositetrahedron. The main driving force of the reconstruction is considered to be the grain boundary energy existing between polycrystalline grains. This process also obeys the mechanism of in situ solid phase reconstruction (Is-SPR). Furthermore, the size and morphology of the zeolite ANA single crystal can be modified by surfactants.

Expression and characterization of Kunitz domain 3 and C-terminal of human tissue factor pathway inhibitor-2.

Human tissue factor pathway inhibitor-2 (hTFPI-2) is a serine protease inhibitor and its inhibitory activity is enhanced by heparin. The Kunitz domain 3 and Cterminal of hTFPI-2 (hTFPI-2/KD3C), which has the activity toward heparin calcium, have been successfully expressed in Pichia pastoris and purified by SPSepharose and heparin-Sepharose chromatography. The Fourier transformed infrared spectroscopy (FTIR), Raman spectroscopy, and circular dichroism (CD) experiment results implied that hTFPI-2/KD3C contained small contents of alpha-helix and beta-strand, but large amounts of random coil and two kinds of disulfide bonds, gauche-gauche-gauche (ggg) and trans-gauchetrans (tgt). The interaction of hTFPI-2/KD3C with heparin calcium was investigated by CD. It was found that heparin calcium induced b-strands in hTFPI-2/ KD3C to different extents depending on the ratio of hTFPI-2/KD3C and heparin calcium.

The NMR solution structure of recombinant RGD-hirudin.

The solution structure of a new recombinant RGD-hirudin, which has the activities of anti-thrombin and anti-platelet aggregation, was determined by (1)H nuclear magnetic resonance spectroscopy and compared with the conformations of recombinant wild-type hirudin and hirudin (variant 2, Lys47) of the hirudin thrombin complex. On the basis of total 1284 distance and dihedral angle constraints derived from a series of NMR spectra, 20 conformers were computed with ARIA/CNS programs. The structure of residues 3-30 and 37-48 form a molecular core with two antiparallel beta-sheets as the other two hirudins. However, significant differences were found in the surface electrostatic charge distributions among the three hirudins, especially in the RGD segment of recombinant RGD-hirudin. This difference may be greatly beneficial to its additional function of anti-platelet aggregation. The difference in extended C-terminal makes its both ionic and hydrophobic interactions with the fibrinogen recognition exosite of thrombin more effective.

Spectroscopic analysis on the effect of temperature on Kunitz domain 1 of human tissue factor pathway inhibitor-2.

The conformation of Kunitz domain 1 of human tissue factor pathway inhibitor-2 (hTFPI-2/KD1) has been studied by fourier transform infrared spectroscopy, circular dichroism, and Raman spectroscopy. It was found that hTFPI-2/KD1 contained approximately 17% alpha-helices, 24% beta-strands, 46% random coils, 13% beta-turns, and two kinds of disulfide bonds(ggg and tgt) at 25 degrees C. The detailed conformational changes of the heated protein observed by fourier transform infrared spectroscopy, circular dichroism and Raman spectroscopy revealed that hTFPI-2/KD1 was thermally stable. However, KD1 could form an intermediate form at high temperature, then return to its normal conformation when the temperature was lowered. Activity assays also showed that hTFPI-2/KD1 was able to keep its inhibitory activity on plasmin after being heated to 80 degrees C for 5 min.

Purification and structural characterization of human ERp29.

ERp29 is a major resident of the endoplasmic reticulum (ER) and is postulated to play an important molecular chaperone role in most animal cells. Human ERp29 was isolated to homogeneity in high yield by using a bacterial expression system. Its secondary structure was studied by circular dichroism (CD), Fourier transformed infrared spectroscopy (FTIR) and Raman spectroscopy and it was found that human ERp29 comprises significant alpha-helical structure. The details of its temperature-induced conformational changes was studied by CD and FTIR for the first time, revealing that the protein is stable below 50 degrees C and has two distinct structural transitions between 50 degrees C and 70 degrees C. This may shed light on ERp29's inability to protect substrate proteins against thermal aggregation.

Structure study of recombinant RGD-hirudin by vibrational and circular dichroism spectroscopy.

The secondary structure of a new type of recombinant RGD-hirudin, which has the activities of anti-thrombin and anti-platelet aggregation, has been studied by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and circular dichroism (CD) methods. The distribution of various secondary structure elements was determined using only a very small amount of sample protein. It was found that the recombinant RGD-hirudin contains about 26% extended chain, 21% beta-turn and 53% unordered structure, leaving no alpha-helix. The results showed that the regular secondary structure of recombinant RGD-hirudin is increased compared with wild-type hirudin. The RGD segment that is located at the end of a long arm of a beta-sheet is thought to play an important role in the additional function of anti-platelet aggregation. Throughout the experiments, FT-IR, Raman spectroscopy and CD generated mutually reinforcing results.

1H NMR assignment and secondary structure of recombinant RGD-hirudin.

The conformation of a new recombinant RGD-hirudin, which has the activities of anti-thrombin and anti-platelet aggregation, was investigated by multi-dimensional NMR spectroscopy. The 1H NMR spectra of this protein are assigned in a sequential manner by using a combination of 2D NMR techniques to demonstrate through-bond and through-space (<5 A) connectivities. The secondary structure of recombinant RGD-hirudin was deduced from chemical shift indices, sequential NOEs and 3J(HNalpha) coupling constants. The results show that the recombinant RGD-hirudin has two anti-parallel beta-sheets and no alpha-helix, and also that the Arg-Gly-Asp (RGD) binding motif of this protein is located at the end of a long arm, which consists of two anti-parallel beta-strands (residues 26-31 and 36-41). As the strands are connected by a beta-turn, the recombinant RGD-hirudin acquires high flexibility and inhibits platelet aggregation more effectively.

Purification and structural study of the beta form of human cAMP-dependent protein kinase inhibitor.

The beta form of human cAMP-dependent protein kinase inhibitor (human PKIbeta), a novel heat-stable protein, was isolated with high yield using a bacterial expression system. Assays of PKI activity demonstrated that purified PKIbeta inhibits the catalytic subunit of cAMP-dependent protein kinase. FTIR, Raman spectroscopy and CD experiments implied that human PKIbeta contained only small amounts of alpha-helix and beta-structures, but large amounts of random coil and turn structures, which may explain its high thermostability. The details of its conformational changes in response to heat were studied by CD experiments for the first time, revealing that the protein unfolded at high temperature and refolded when decreased to room temperature.