Helix propagation and N-cap propensities of the amino acids measured in alanine-based peptides in 40 volume percent trifluoroethanol.

The helix propagation and N-cap propensities of the amino acids have been measured in alanine-based peptides in 40 volume percent trifluoroethanol (40% TFE) to determine if this helix-stabilizing solvent uniformly affects all amino acids. The propensities in 40% TFE are compared with revised values of the helix parameters of alanine-based peptides in water. Revision of the propensities in water is the result of redefining the capping statistical weights and evaluating the helix nucleation constant with N-capping explicitly included in the helix-coil model. The propagation propensities of all amino acids increase in 40% TFE relative to water, but the increases are highly variable. In water, all beta-branched and beta-substituted amino acids are helix breakers. In 40% TFE, the propagation propensities of the nonpolar amino acids increase greatly, leaving charged and neutral polar, beta-substituted amino acids as helix breakers. Glycine and proline are strong helix breakers in both solvents. Free energy differences for helix propagation (delta delta G) between alanine and other nonpolar amino acids are twice as large in water as predicted from side-chain conformational entropies, but delta delta G values in 40% TFE are close to those predicted from side-chain entropies. This dependence of delta delta G on the solvent points to a specific role of water in determining the relative helix propensities of the nonpolar amino acids. The N-cap propensities converge toward a common value in 40% TFE, suggesting that differential solvation by water contributes to the diversity of N-cap values shown by the amino acids.     

Inhibition of TRAP-induced angiogenesis by the tripeptide Phe-Pro-Arg, a thrombin-receptor-derived peptide analogue

Summary We have recently shown that thrombin promotes angiogenesis by a mechanism independent of fibrin formation. In the present paper, we investigated the effect of the thrombin-receptor-activating tetradecapeptide (TRAP_1–14, S₄₂FLLRNPNDKYEPF₅₅) for its effects on angiogenesis in the chick chorioallantoic membrane (CAM) system of angiogenesis. A dose-dependent promotion of angiogenesis is evident with TRAP. In contrast, a thrombin-receptor-derived tripeptide analogue H-Phe-Pro-Arg-OH (FPR), which was designed based on the S₄₂FLLR₄₆ sequence, caused an inhibition of angiogenesis in the CAM, and when it was combined with TRAP it caused a complete reversal of the angiogenesis-promoting effect of TRAP. These results indicate that the proteolytic exposure of the receptor N-terminal tetradecapeptide by thrombin can activate the post-thrombotic events related to angiogenesis. These events can be modulated by constrained peptide analogues such as FPR.     

Solid-phase synthesis of triple-helical collagen-model peptides

Summary The triple-helical conformation of collagen has been proposed to be important for mediation of cellular activities, such as adhesion and activation, extracellular matrix assembly, and enzyme function. We have developed synthetic protocols that allow for the study of biological activities of specific collagen sequences in triple-helical conformation. These methods primarily involve solid-phase assembly and covalent linkage of three peptide chains. The resultant triple-helical peptides have sufficient thermal stabilities to permit structural and biological characterization under physiological conditions. The present article critically reviews the various approaches for constructing synthetic triple-helices.This paper is based on a presentation given at the Symposium on Peptide Structure and Design as part of the 31st Annual ACS Western Regional Meeting held in San Diego, CA, USA, October 18–21, 1995.     

以人工合成多肽为抗原的戊型肝炎病毒抗体检测方法的建立和评价

酶联法是ＨＥＶ感染的主要检测方法,多采用基因表达产物为抗原。近来由于人工合成多肽抗原克服了基因重组抗原制备复杂、非特异结构多、难以纯化的缺点,已广泛用于多种病毒感染的检测。根据已发表的ＨＥＶ氨基酸序列的保守性及亲水性等特点,设计合成了两个多肽ＥＳＰ１和ＥＳＰ２,分别位于ＯＲＦ２和ＯＲＦ３区,以此为混合抗原建立了检测ＨＥＶ抗体的间接ＥＬＬＳＡ法,与市售优质试剂比较,其阳性符合率为９７．７５％,阴性符合率为９９．４３％,总符合率为９８．８６％。该方法灵敏度高、特异性强、安全快速,是检测ＨＥＶ感染和流行病学调查的理想方法。     

被囊动物中生物活性物质研究的一些进展

本文对近年从海鞘中提取分离的环肽类及生物碱类化合物作了综述,对一些典型化合物如Didemnins、Patellamides、Merdine、Eudistomins及Ecteinascidins等作了较详细的介绍。     

Solid-phase Synthesis and Cellular Localization of a C- and/or N-terminal Labelled Peptide

We report the solid-phase synthesis by the Fmoc strategy of a peptide containing a cysteamide group at its C-terminus. This peptide was subject to further modifications including the linkage of fluorophores, namely lucifer yellow and coumarin respectively, at the C- and/or N-terminals. After incubation with living cultured cells these two probes were localized and it is concluded that the post-synthesis modifications can strongly modify the localization of the peptide.     

Folded Structures in Protonated Reduced Dipeptides

Reduced dipeptides with the general formula RCO-Xaa- rXbb-N⁺HR′R′′ (rXbb, reduced analogue of residue Xbb: NH-C^α HR¹ -C_r H₂) are shown to adopt a folded conformation in solution and in the solid state. The protonated reduced amide bond is an active proton donor capable of interacting with a peptide carbonyl to give a strong hydrogen bond topologically equivalent to the i+2 or i+3? i interaction. The resulting conformation is similar to the γ- or β-turn structure found in peptides and proteins.     

Pro-Thyrotropin-Releasing Hormone Processing by Recombinant PC1

Abstract: Pro-thyrotropin-releasing hormone (proTRH) is the precursor to thyrotropin-releasing hormone (TRH; pGlu-His-Pro-NH₂), the hypothalamic releasing factor that stimulates synthesis and release of thyrotropin from the pituitary gland. Five copies of the TRH progenitor sequence (Gln-His-Pro-Gly) and seven cryptic peptides are formed following posttranslational proteolytic cleavage of the 26-kDa rat proTRH precursor. The endopeptidase(s) responsible for the physiological conversion of proTRH to the TRH progenitor form is currently unknown. We examined the in vitro processing of [³H]leucine-labeled or unlabeled proTRH by partially purified recombinant PC1. Recombinant PC1 processed the 26-kDa TRH precursor by initially cleaving the prohormone after the basic amino acid at either position 153 or 159. Based on the use of our well-established antibodies, we propose that the initial cleavage gave rise to the formation of a 15-kDa N-terminal peptide (preproTRH_25–152 or preproTRH_25–158) and a 10-kDa C-terminal peptide (preproTRH_154–255 or preproTRH_160–255). Some initial cleavage occurred after amino acid 108 to generate a 16.5-kDa C-terminal peptide. The 15-kDa N-terminal intermediate was further processed to a 6-kDa peptide (preproTRH_25–76 or preproTRH_25–82) and a 3.8-kDa peptide (preproTRH_83–108), whereas the 10-kDa C-terminal intermediate was processed to a 5.4-kDa peptide (preproTRH_206–255). The optimal pH for these cleavages was 5.5. ZnCl₂, EDTA, EGTA, and the omission of Ca²⁺ inhibited the formation of pYE₂₇ (preproTRH_25–50), one of the proTRH N-terminal products, by 48, 82, 72, and 45%, respectively. This study provides evidence, for the first time, that recombinant PC 1 enzyme can process proTRH to its predicted peptide intermediates.     

Natriuretic Peptides Inhibit Nicotine-Induced Whole-Cell Currents and Catecholamine Secretion in Bovine Chromaffin Cells: Evidence for the Involvement of the Atrial Natriuretic Factor R2 Receptors

Abstract: There is increasing evidence that members of the natriuretic peptide family display sympathoinhibitory activity, but it remains uncertain which receptor pathway is implicated. We performed cyclic GMP production studies with chromaffin cells treated with either atrial natriuretic factor (ANF) or C-type natriuretic peptide (CNP) and found that these cells specifically express the ANF-R_1C but not the ANF-R_1A receptor subtype. Evidence for the existence of ANF-R₂ receptors was obtained from patch-clamp experiments where C-ANF, an ANF-R₂-specific agonist, inhibited nicotinic currents in single isolated chromaffin cells. Involvement of ANF-R₂ receptors in the modulation of nicotinic currents was further supported by the significant loss of this inhibitory activity after the cleavage of the disulfide-bridged structure of C-ANF. This linearized form of C-ANF also displayed a lower binding affinity for ANF-R₂ receptors. Like the patch-clamp studies, secretion experiments demonstrated that both CNP and C-ANF are equally effective in reducing nicotine-evoked catecholamine secretion by cultured chromaffin cells, raising the possibility that this effect of CNP is predominantly mediated by the ANF-R₂ and not the ANF-R_1C receptors. Finally, this response appears to be specific to nicotinic agonists because neither histamine- nor KCI-induced secretions were affected by natriuretic peptides. In the present study, we report (1) the presence of ANF-R_1C and ANF-R₂ receptor subtypes in bovine chromaffin cells, (2) the inhibition by natriuretic peptides of nicotinic whole-cell currents as well as nicotine-induced catecholamine secretion, (3) the possible mediation of these effects by the ANF-R₂ class of receptors, and (4) the specificity of this inhibition to nicotinic agonists. Because bovine chromaffin cells release ANF, BNP, and CNP together with catecholamines, all three peptides might exert negative feedback regulation of catecholamine secretion in an autocrine manner by interacting with the nondiscriminating ANF-R₂ receptor subtype.     

A VIP hybrid antagonist: From developmental neurobiology to clinical applications

Summary 1. The 28 amino acid vasoactive intestinal peptide, VIP, was originally isolated from the intestine, following a bioassay measuring vasodilating properties. Immunocytochemistry, receptor binding assays and in situ hybridizations have demonstrated VIP abundance in the nervous system, suggesting multiple bioactivities.2. A pharmacological approach was chosen to dissect VIP activities and a prototype VIP antagonist (Met-Hybrid) consisting of a carboxyl fragment of VIP_7–28 and a six amino acid fragment of neurotensin, neurotensin_6–11-VIP_7–28 was synthesized.3. This hybrid peptide was designed to maintain the binding capacity of one parent molecule (VIP), while loosing the agonistic properties, representing a classical competitive receptor antagonist. Furthermore, the new molecule exhibited increased specificity to central nervous system VIP receptors.4. The Met-Hybrid was originally discovered as a potent inhibitor of VIP functionin vivo. In the adult rodent, acute administration of the antagonist resulted in blockade of VIP-mediated potentiation of sexual behavior and chronic intracerebroventricular application impaired VIP-associated learning abilities. During ontogeny, chronic injections of the molecule resulted in neuronal damage, disruption of the diurnal rhythmicity of motor behavior, and retardation in the acquisition of neonatal reflexes in the rat.5. During gestation, severe microcephaly was induced by acute administration of the Met-Hybrid to pregnant mice. The hybrid antagonist inhibited VIP-stimulated mitosis in whole embryo cultures and in a variety of cancer cell linesin vitro andin vivo, suggesting therapeutical potential.