Peptide research最新文献

Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS), a well-suited method for the characterization of peptides and proteins, was used for analysis of protected peptide fragments. It is shown that acidic matrices, e.g. 2,5-dihydroxybenzoic acid, frequently used in MALDI-TOF MS of peptides, causes partial cleavage of acid-labile side-chain protecting groups. Because this effect is strongly related to the matrix used, the observed deprotection can be avoided by choosing an appropriate matrix such as 2,4,6-trihydroxyacetophenone or 2-amino-5-nitropyridine. The advantage of neutral matrix compounds for MALDI-TOF analysis of protected peptides is clearly demonstrated, confirming the potential of MALDI-TOF mass spectrometry.

The role of specific amino acid residues within the sequence region between Leu26 and Thr46 of the human follicle-stimulating hormone (hFSH) alpha-subunit in the FSH-receptor interaction has been investigated. Competitive binding activities of seven sets of synthetic peptides were evaluated with both FSH- and luteinizing hormone (LH)-radioreceptor assay procedures. Set 1 included two overlapping peptides (alpha 25-41 and alpha 31-45) spanning the alpha 26-46 region, while Sets 2-6 included peptides of different size or structure in which the alpha 26-46 sequence was (i) sequentially truncated either from the N-terminus or from the C-terminus or both; (ii) alternatively reduced to a series of overlapping 13-mer peptides; or (iii) modified at the C-terminal Arg and Lys residues with substitution by Ala residues. In Set 7, synthetic peptides related to the parent alpha 26-46 peptide were prepared in which all the cysteine residues were substituted either singly or multiply with serine residues (i.e., alpha 26-46 Cys28,31,32-->Ser28,31,32). The ED50 values of the parent alpha 26-46 peptide in the FSH-radioreceptor assay were 2 and 7 x 10(-5) M, depending on whether the C-terminus was present as the amide or the free acid form, respectively. The substituted peptide alpha 26-46 (Cys28,31,32-->Ser28,31,32) was totally inactive in the FSH-radioreceptor assay. The truncation studies indicated that Cys28, Cys31 and Cys32 all contribute to the hormone-receptor interaction, with Cys32 being the major contributory cysteine residue. Similar results were observed when these peptides were evaluated in the LH-radioreceptor assay where the ED50 value for the parent alpha 26-46 peptide was observed to be 2 or 3 x 10(-5) M, depending on whether the C-terminus was the amide or the free acid. The Cys31 residue did not appear to contribute to the LH-receptor interaction; however, removal of Cys28 and Cys32 resulted in significant decreases in binding activity. The C-terminal truncation studies of the alpha 26-46 peptide revealed that Lys44 contributes to FSH receptor binding activity but does not contribute to the LH-receptor interaction. Truncation of the Arg42 residue or substitution of Arg42 with alanine in the alpha 31-45 peptide sequence prepared as part of the Set 1 synthetic peptides (i.e., the alpha 31-45 Arg42-->Ala42 peptide) or as part of the Set 6 peptide series, alpha 26-46 Arg42-->Ala42, confirmed the involvement of this residue in the LH-receptor interaction.(ABSTRACT TRUNCATED AT 400 WORDS)

Conformationally constrained peptidomimetics are being increasingly used in the development of 3-D pharmacophores of peptide-based drug candidates and to alter their metabolic stability towards achievements of oral bioavailability. Here we present conformational energy calculations on model compounds containing 1-aminocyclobutane carboxylic acid (ACBC) and its derivatives using molecular mechanics methods. The low-energy models adopt conformations characteristic of a variety of regular structures such as the alpha-helix, 3(10)-helix, gamma-turn and polyproline-II-type three- and fourfold helices. The energetically most favored models adopt the gamma-turn (2.2(7) helix) conformation or alpha-/3(10)-helical conformation, both of either handedness, depending on the substituents on the cyclobutane. These results are qualitatively consistent with the crystal structures of peptide analogs containing ACBC and have implications for the design of peptidomimetics.

Two synthetic combinatorial libraries (SCLs) were prepared, each composed of 52,128,400 L-amino acid hexapeptides, one with and the other without an N-terminal acetyl moiety. The two libraries were used in conjunction with an iterative selection process to identify individual peptides capable of inhibiting the binding of the mu-selective opioid peptide [3H]-[D-Ala2,MePhe4,Gly-ol5]enkephalin to rat brain homogenates. As reported previously, when using the nonacetylated SCL the first five residues identified corresponded exactly to methionine- and leucine-enkephalin, both of which are endogenous opioid peptides. The iterative identification process has now been completed for two additional mixtures found to have activity in the initial screening of this SCL. Two new series unrelated to the enkephalins have been identified: YPFGFO-NH2 and WWPKHO-NH2 (where O = one of the 20 L-amino acids). Individual peptides from each of these were found to be agonists at the mu receptor and have high affinity (IC50 values of the most active peptides were 10-15 nM) and selectivity for the mu receptor. In addition to the acetalins (described previously), two new series have now been identified from the acetylated library: Ac-FRWWYO-NH2 and Ac-RWIG-WO-NH2 (IC50 values of the most active peptides were 5-30 nM). Ac-FRWWYM-NH2 was determined to be an agonist at the mu receptor, whereas Ac-RWIGWR-NH2 was found to be an antagonist at this receptor.

Pseudo-prolines (psi Pro) are introduced as a temporary protection technique for serine, threonine and cysteine side chains in standard Fmoc/tBu solid-phase peptide synthesis (SPPS). The incorporation of these novel building blocks into a growing peptide chain proceeds by means of the coupling of preformed, suitably protected psi Pro dipeptides. For the example of representative model peptides used in protein de novo design, the potential of psi Pro to solubilize otherwise sparingly or completely insoluble peptides is demonstrated. Because of their intrinsic propensity for preventing peptide aggregation and beta-sheet formation, pseudo-prolines offer new possibilities for accessing large peptides by convergent strategies and chemoselective ligation techniques.

Retro-inverso analogues of peptides corresponding to the major antigenic site 141-159 of VP1 from two foot-and-mouth disease virus variants have been synthesized and tested for their antigenic and immunogenic properties. Antibodies to the L- and retro-inverso peptides were produced by injecting rabbits with peptides covalently coupled to small unilamellar liposomes containing monophosphoryl lipid A as adjuvant. When compared to the antibody response raised against the L-peptides, the duration of the IgG response that was induced by the retro-inverso peptides was significantly longer and the titer of anti-peptide antisera was much higher. Antibodies to retro-inverso peptides cross-reacted equally well with the respective parent L-peptides. These results, obtained with a viral sequence which was found previously to represent a good candidate for possible vaccination, show that retro-inverso peptidomimetics could be useful for enhancing the immunogenicity of peptides.

The x-ray diffraction structure analyses of the L-enantiomeric and racemic forms of the 2-(1'-benzyloxycarbonylamino-1'-methyl) ethyl-4-benzyl-oxazol-5(4H)-one, the Goodman oxazolone, have been performed. In the crystal state the oxazolone ring of the enantiomeric compound is nearly sandwiched between the two phenyl rings, whereas in the racemate the phenyl ring of the N alpha-protecting group moves away from the oxazolone ring.

A systematic approach to map the functionally important determinants of endothelin-1 (ET-1) by a D-amino acid scan is described. Correct orientation of the amino acid side chains was generally of paramount importance both for binding at the ETA receptor and for contracting activity. This was particularly valid for positions 2, 8, 14, 16-21 (the four Cys residues were kept unaltered). Nevertheless, increment of binding affinity was observed by inversion of configuration at positions 6, 7, 9 and 10. In addition, [D-Lys9]ET was an agonist about four times more potent than the natural compound. Usually both 1,4- and 1,3-isomers (corresponding, respectively, to the correct and misfolded disulfide bridges of ET) were obtained, and usually the isomer formed in larger amount had the higher HPLC retention time and the higher biological activity. However, four out of seventeen single-point D-amino acid analogues could be isolated only in one isomeric form. In three cases (D-Ser2, D-Ser4, D-Val12), the inverted amino acid was adjacent to a Cys residue, and in one case (D-Lys9) it was one amino acid apart, thus suggesting a possible effect of the bridged cysteinyl residues in isomeric selectivity.

We previously reported purification of a protein (approximately equal to 57 kDa) from human follicular fluid having FSH binding inhibitory (FSH-BI) activity. Purified hFSH-BI was cleaved with cyanogen bromide and trypsin. The resulting peptide fragments were separated by HPLC and sequence information for individual fragments was obtained. A ten amino acid sequence of hFSH-BI derived from this procedure was identified, and a corresponding peptide amide (BI-10) was synthesized and utilized for further study. A protein database search revealed no significant identity between this decapeptide and other known proteins. We examined the ability of BI-10 to inhibit binding of 125I-hFSH to FSH-receptor enriched bovine testes membranes utilizing a radioligand receptor assay (RRA). BI-10 inhibited binding of 125I-hFSH to its receptor in a concentration-related manner, with an ED50 of 300 microM. BI-10 had no effect on 125I-hCG binding to receptor even at concentrations up to 1000 microM, suggesting that the effect of BI-10 was specific for the interaction between FSH and its receptor. To assess bioactivity of BI-10, we investigated its effect on FSH-stimulated conversion of androstenedione to estradiol by rat Sertoli cells in primary culture in vitro. Inhibition of FSH-stimulated estradiol synthesis (FSH antagonist activity) was significant at a BI-10 concentration of 1000 microM. BI-10 also significantly inhibited FSH-stimulated cAMP accumulation in primary cultures of Sertoli cells when examined at the same concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

The retention behavior of a series of amphipathic peptide multimers based on the amino acid sequence [KSEEQLA]n has been investigated using reversed-phase high performance liquid chromatography (RP-HPLC). Structure-retention parameters which are related to the hydrophobic contact area and affinity of these peptides for the immobilized hydrocarbonaceous ligands were determined over a range of operating temperatures between 5 degrees and 85 degrees C. The influence of ligand hydrophobicity was assessed by comparison of peptide retention behavior using an n-octadecyl (C18)- and an n-butyl (C4)-silica of similar ligand density. The results demonstrated that ligand-mediated conformational effects can stabilize peptide structure depending on the chromatographic residence time and peptide length. In particular, more highly stabilized secondary structures were evident for the longer peptides. In addition, the amphipathic secondary structure of the peptides were more effectively stabilized by the more hydrophobic C18 ligands relative to the shorter C4 ligands. Additional information on the interactive dynamics of these peptide multimers was obtained from analysis of bandwidth dependencies under the different chromatographic conditions. These studies provide further insight into the role which hydrophobic forces can play in the stabilization of peptide structures.