Biomedical peptides, proteins & nucleic acids : structure, synthesis & biological activity最新文献

The localization and co-localization of pituitary adenylate cyclase activating polypeptides (PACAPs) and vasoactive intestinal polypeptide (VIP) in the enteric nerve plexus of the guinea pig jejunum were immunohistochemically compared by the peroxidase anti-peroxidase (PAP) method using region-specific antisera against PACAP38, PACAP27 and VIP, respectively. Immunoreactive nerve elements were demonstrated in the ganglia of both myenteric and submucous plexi in the guinea pig jejunum. Numerous immunoreactive nerve cell bodies were localized in the myenteric ganglia, while nerve cell bodies in the submucous ganglia were only slightly immunopositive. Immunoreactive nerve terminal varicosities occurred in both myenteric and submucous ganglia. Additionally, PACAPs-immunoreactive nerve cell bodies were also immunopositive with VIP. Thus, both PACAP38 and PACAP27, as well as VIP, are co-localized in the cell bodies of guinea pig jejunum.

The methodology for the incorporation of azaamino-acid residues into peptides synthesised by a solid-phase method has been extended to allow azaalanine peptides to be prepared. In this way, Ac-Leu-Ser-Gly-azaAla-Gly-Phe-Ser-Leu-NH2 H-Ala-Ala-Lys-Glu-Ala-Ala-Glu-Ala -Ala-Glu-Lys-Ala-azaAla-Glu-Leu-Ala-Leu-N2H3, and H-Ala-azaAla-Lys-Glu-Ala-Ala-Glu-Ala-Ala-Glu-Lys-Ala-Ala-Glu-Leu-A la-Leu-N2H3 have been prepared. A new analogue of the Ala-Gly sequence, 3-azaalanylpropionic acid has been prepared and used to prepare the peptide analogue acetyl-Leu-Ser-Gly-azaAla-3-Prop-Phe-Ser-Leu-NH2.

The study was aimed to explore the possible involvement of the acute phase HDL apolipoprotein, serum amyloid A (SAA) in the regulation of PGI2 production by endothelial cells. This, in view of the recent detection of SAA mRNA in endothelial cells of human atherosclerotic lesions. Human SAA induces PGI2 formation in bovine aortic endothelial cells culture in a concentration relevant to moderate acute phase events. 50 micrograms/ml of purified human SAA increases PGI2 production from a mean basal level of 2,490 +/- 330 pg/ml by 1.80 +/- 0.1 fold (n = 10; p < 0.01). The PGI2 inducing activity resides apparently in the N-terminal, i.e. amino acid residues 1-14, of the SAA molecule, 50 micrograms/ml of the peptide induces 2.9 +/- 0.5 fold increase of PGI2 production (n = 4; p < 0.03). TNF and LPS each induce PGI2 production in a concentration and time dependent manner. TNF in concentration of 10 ng/ml induces, in the presence of calf serum, an increase of 24.9 +/- 2.3 fold (n = 4; p < 0.001) and LPS in concentration of 1 microgram/ml causes a 18.3 +/- 1.3 fold increase, (n = 4; p < 0.01). In serum-free cultures, only a 2.5 +/- 0.3 fold increase was detected by 10 ng/ml TNF (n = 4), and a 5.9 +/- 0.4 by 1 microgram/ml of LPS. Thus, serum has a strong effect on PGI2 induction. When 50 micrograms/ml SAA is coadministered with 1 ng/ml TNF it reduces the TNF-induction of PGI2 from 7.7 +/- 2.8 to 3.3 +/- 1.2 fold (n = 4; p < 0.01). SAA attenuates, as well, LPS-mediated activity, although in a less pronounced manner. Our finding suggest a potential physiological function for SAA in regulation of basal and cytokine-induced PGI2 production by vascular endothelium. The capacity of SAA to markedly moderate PGI2 induction by TNF and LPS suggest that it may play a role in defending against vessel damage, in cases of atherosclerosis, bacterial infection or septic shock. The induction of PGI2 by SAA through its N-terminal domain, which also exhibits an anti-platelet aggregation activity, suggests a potential therapeutical use for this peptide as an anti-hypertensive and an anti-aggregatory agent.

The peptide encoded for by one of the two relaxin genes found in the human genome, designated H1, has been synthesized by the Boc-polystyrene solid phase method. The two chains which constitute relaxin, A- and B-, were assembled separately and, after cleavage, deprotection and purification, combined in solution at high pH to form the one intra- and two intermolecular disulfide bonds. Comprehensive chemical characterization including ion spray mass spectrometry of the peptide confirmed both its correct identity and high purity. The synthetic H1 relaxin was analyzed by circular dichroism spectroscopy and shown to possess a greater alpha-helical conformation in water than the corresponding H2 relaxin. The peptide had powerful direct chronotropic and inotropic effects in the isolated rat heart assay as did an analogue of the peptide in which the C-terminus of the B-chain was extended by four residues.

Human ras-GTPase-activating protein (GAP120) SH3-domain-binding protein (G3BP) has recently been identified on the basis of its specific binding to the GAP120 SH3 binding domain. Here we report the identification of a mouse G3BP cDNA and the confirmation by three dimensional modelling of an RNA recognition motif (RRM) in the encoded protein. Mouse G3BP also contains an RGG domain, an acid-rich amino acid domain, and several SH3 domain-binding consensus sequences, indicating that mammalian G3BPs represent a new family of signal transduction proteins which connect tyrosine kinase-linked receptors to cellular RNA metabolism.

Analogs of the peptide Val-Thr-Val-Ala-Pro-Val-His-Ile, derived from the primary sequence of the acute phase reactant CRP, i.e. amino acid residues 89-96, were optimized to inhibit the enzymatic activities of human leukocyte elastase (hLE) and human leukocyte cathepsin G (hCG), which are associated with tissue damage occurring in the course of several chronic inflammatory conditions. hLE's major S1 pocket, lined mostly by hydrophobic amino acid residues, was shown by theoretical electrostatic potential calculations to possess some negative charge. This pocket was found to be extremely sensitive towards modifications in the P1 position of CRP derived inhibitors, with valine being the preferred amino acid. In contrast, the corresponding S1 pocket of hCG is large and accepts the positively charged 'aromatic' side chain of histidine, which increases most significantly the capability of CRP derived inhibitors. A prominent positive pocket was observed in the distant S7 region of hLE, which is generated by two exposed positive residues, Arg177 and Arg217, on the enzymes surface. This long range subsite was utilized to increase the hLE inhibitory activity of CRP derived peptide using the natural sequence of CRP, which contains a unique glutamic acid moiety in the P7 position. In contrast to the charged nature of hLE's S7 pocket, the corresponding pocket on the surface of hCG appears to be less prominent. Additional hydrophobic N-terminus modifications of CRP89-96 increased the inhibitory activity towards both enzymes, provided that residues P1 and p7, were designed according to the individual preferences of hLE and hCG. The unique interaction between the negative amino acid side chain of CRP with the positive S7 pocket of hLE as elucidated in this study, and additional subsite preferences may now be used in the design of novel therapeutic substances.

Based on the CDR3 V(H) sequence of a monoclonal antibody (ASM2) raised against epithelial cancer cells, the synthetic peptide YCAREPPTRTFAYWG (EPPT1) has been found to have an appreciable affinity (Kd = 20 microM) for the deglycosylated mucin-derived peptide antigen YVTSAPDTRPAPGST (PDTRP). The technetium-radiolabelled form of this peptide has been found to be a good tumour-imaging candidate for diagnosis of breast carcinoma. Several EPPT1 peptide analogues were synthesised. A differential biostability was obtained blocking the end groups of EPPT1. The susceptibility to proteolytic degradation was significantly decreased for the C-amidated form of EPPT1 than the N-acetylated form. Using resonant mirror biosensor technique, the EPPT1 analogues were classified as active and non-active peptides according to their PDTRP-binding properties. The binding of EPPT1 to PDTRP in free solution was also determined unambiguously by CD spectroscopy. CD spectra of both active and non-active peptides showed the presence of irregular conformations in H2) and SDS above cmc. In TFE, significant degree of ordered conformations of alpha-helix or beta-turn type were induced but did not correlate well with their binding properties. In SDS below cmc a conformational difference was observed between the active and non-active peptides. The active peptides exhibited CD spectra of aggregation of beta-strand type whilst the non-active showed CD spectra similar to those in H2O and SDS above cmc, critical micelle concentration. A good correlation between the extended conformation of beta-strand type and the binding affinity of the active peptides suggests this conformation as the binding feature of the EPPT tumour-imaging peptides. These information are vital for the design of novel EPPT analogues. Any modification to improve binding affinity must retain the ability of the peptides to adopt the extended conformation of beta-strand type.

The peptide hormone relaxin was isolated in good yield from the ovaries of the pregnant rodent Rattus rattus using a simplified purification schedule. It was subjected to comprehensive chemical characterization to confirm both its purity and predicted composition. The peptide was also chemically synthesized by the solid phase procedure. The two chains comprising the hormone were each assembled by the Boc-polystyrene method and, following conventional purification, combined in solution to form the single intramolecular and two intermolecular disulfide bonds. Following purification, the synthetic rat relaxin was fully chemically characterized and shown to be indistinguishable from the native peptide including by secondary structure analysis using circular dichroism spectroscopy. The native and synthetic rat relaxins were shown to be equally biologically active in the in vitro rat uterine relaxation assay and had pEC50 values that were comparable to synthetic human H2 relaxin.

The C-terminal pentapeptide of peptide T (T5) and a glycosylated analogue (T5GlcNAc) were investigated using 1H NMR spectroscopy to examine the influence of the sugar on the secondary structural characteristics of the peptide. The NMR data confirm the presence of a turn structure amongst an ensemble of predominantly randomly structured species in a solution of 83% TFE/H2O for both peptides. This is in agreement with a previous CD analysis demonstrating the presence of beta-turn. Unlike the CD study, the NMR data do not show a difference in the time-averaged conformation of the glycosylated versus non-glycosylated peptide. These studies suggest that any sugar-peptide interactions which occur in this system are transient in nature, and that they do not greatly influence the local secondary structural characteristics of the peptide. In particular, the turn predisposition already exhibited by the peptide appears to be neither enhanced nor reduced by a neighbouring natural N-glycosylation site. This finding is likely to be of general interest, given the importance of glycosylation as a post-translational modification and that its role in determining protein structure has yet to be characterized.