Peptide research最新文献

Reversed phase high-performance liquid chromatography with chemiluminescent nitrogen detection (HPLC-CLND) was used for the quantitative analysis of peptides manufactured by solid-phase peptide synthesis. CLND provided quantitative information regarding the nitrogen distribution of peptide samples following HPLC separation. This technique permits the universal quantitation of the "peptide content" of synthetic peptides in an on-line mode without pre- or post-column derivatization and free of interference from non-nitrogen-containing UV chromophores. This paper will show the utility of this novel technique in measuring the peptide content of crude synthetic proinsulin chain C peptide. A mixture of five reference peptides was analyzed to show the homogeneity of the CLND response and used to determine peptide content. Application for the purified product is also discussed. The detection profiles were acquired in parallel with a UV detector.

Previous theoretical analysis of the primary structure of lung surfactant protein SP-B indicates a disulfide-linked, hydrophobic midsequence that forms a hairpin-like motif. Here, we experimentally investigate the secondary structure of the disulfide-stabilized bend region by synthesizing two 12-residue analogs of the SP-B midsequence. The native peptide has the same sequence for residues 35 to 46 as native human SP-B, while, in the second mimic peptide, Leu40 and Val41 were replaced with D-Ser and L-His. Both peptides contain cysteine residues at the N- and C-terminus (Cys35 and Cys46, respectively). Oxidation/reduction experiments with fast atom bombardment mass spectrometry showed mass shifts of approximately 2 daltons, consistent with the oxidized peptides existing in solution as monomers, each with one internal disulfide bond (Cys35-Cys46). Since circular dichroism and Fourier-transform infrared measurements show that both peptides assume turn conformations in structure-promoting solvents such as trifluoroethanol (TFE), a structural model is proposed in which Cys35 and Cys46 are brought in close apposition through an internal bend in the peptide. Consistent with this model are electron spin resonance (ESR) results of the mimic peptide nitroxide spin-labeled at Cys35 and Cys46. For the double spin-labeled mimic peptide in TFE. ESR spectra indicated broadening characteristic of either radical interactions or decreased mobility, or both. Increases in radical interactions for the double spin-labeled mimic peptide would be expected for Cys35 and Cys46 approaching within 14 A in structure-promoting solvents, while decreases in spin-label mobility could be due to the formation of a loop. Based on these observations with peptide analogs, residues 35 to 46 probably form a similar bend in the full-length protein.

HIV-1 aspartic protease (PR) is a promising target for acquired immunodeficiency syndrome (AIDS) therapy, and the development of PR inhibitors can be accelerated by computer-aided design methods. We describe an approach for the design of new inhibitors, based on the modification of a known reference inhibitor, and the calculation of relative binding energies, taking into account contributions from all species in the binding equilibrium (inhibitor, PR and inhibitor/PR complex), as well as their solvation. This allows for a rational selection of new structures that are likely to have increased inhibition potency. We have analyzed reduced amide bond hexapeptides (Ac-P3-P2-P1-phi[CH2-NH]-P1'-P2-P3'-NH2), based on the structure of the known inhibitor MVT-101. A maximum gain in binding energy (approximately -55 kcal/mol) is observed when Phe or Tyr are present in positions P1 and P1', Glu in position P2' and aromatic residues (Phe, Trp or Tyr) in positions P3 and P3', while, in general, the presence of positively charged residues is destabilizing. This specificity is explained in terms of the interaction of individual inhibitor residues with proximal and distal PR residues. The validity of this computational approach has been confirmed by solid-phase synthesis of several of the designed pseudopeptides, followed by in vitro enzyme inhibition assaying. The best candidate structures show IC50 values in the low nanomolar range.

To identify B-cell epitopes of the Plasmodium falciparum 25-kDa ookinete protein, Pfs25, 41 overlapping synthetic peptides spanning the entire length of the protein were used individually to immunize CAF1 (F1 hybrid of BALB/c female and A/J male) mice. Antipeptide sera were tested for reactivity to live intact zygote/early ookinete (post-fertilization stage) by immunofluorescence, and by Western blot analysis under nonreducing and reducing conditions, immunoprecipitation of 35S-cysteine-labeled antigen, and ELISA using a vaccinia recombinant Pfs25 antigen. Fourteen B-cell epitopes were identified. These peptides were immunogenic only when administered with high-dose recombinant interleukin-2. Antibodies to 11 peptides recognized only the native conformational structure, one peptide induced antibodies that recognized both reduced and native protein, and two other peptides, after primary immunization, made antibodies to denatured Pfs25, but after boosting the antibodies reacted to both denatured and native Pfs25. Anti-sera to peptides in the first (peptide 7) and fourth (peptide 34) epidermal growth factor-like domains of Pfs25 reacted most strongly with zygotes/ookinetes by immunofluorescence assay. The antibodies elicited by immunization with peptide 34 suppressed infectivity of the parasite to mosquitoes. We further observed that the secondary structure of Pfs25 may be important for immunogenicity because monoclonal antibodies (MAbs) 1C7 and 1D2, both transmission-blocking MAbs, protected enzyme cleavage sites in Pfs25 from proteolysis, suggesting that discontinuous segments of Pfs25 may come together to form immunogenic epitopic sites. Thus, definition of B- and T-cell epitopes may be required to construct a Pfs25 vaccine for optimum immunogenicity.

A solid-phase supported peptide synthesis (SPPS) strategy using p-nitrobenzyl (pNB) esters, thioethers and carbamates for side-chain protection is described. The synthesis of Fmoc p-nitrobenzyl side-chain protected amino acids of lysine, cysteine, glutamic acid and aspartic acid are synthesized and incorporated into the synthesis of tetramers by standard Fmoc methodology using Wang polystyrene resins. Deprotection is carried out on resin in mildly acidic reducing conditions, using a solution of DMF, SnCl2, phenol and HOAc. The yellow by-products associated with the deprotection of the pNB protecting group are then removed by treatment with a solution of benzene sulfinic acid in DMF. The methodology is successfully extended in the synthesis of a peptide with multiple pNB protecting groups.

PMP-D2, a 35-residue peptide containing three disulfide bonds, was synthesized on solid-phase using 9-fluorenylmethoxy-carbonyl (Fmoc) as alpha-NH2 protection and simultaneous air oxidation of the six cysteines for formation of its disulfide bonds. The overall yield was 13%. As very little research has been done on the regioselective formation of three disulfide bonds, we decided to investigate different strategies using either trityl (Trt), acetamidomethyl (Acm) and methoxybenzyl (Mob), or methoxytrityl (Mmt), trityl and acetamidomethyl, as cysteine-protecting groups and Fmoc as alpha-NH2 protection. In the first strategy, the first disulfide bond was formed by air oxidation and the second was formed by iodine oxidation of the Cys(Acm). Then, the Cys (Mob) was deprotected using TFMSA/TFA treatment for formation of the third disulfide bond. This last step was poorly reproducible on a large scale. The overall yield was 2.5%. In the second strategy, the first disulfide was formed on the resin after removal of the methoxytrityl group, and the two remaining disulfide bonds were formed classically in solution. The overall yield was 2%. From the overall yields using these strategies, it appears clear that simultaneous oxidation of the six cysteines is particularly appropriate for the synthesis of PMP-D2.

We demonstrated that a synthetic peptide (EWDREINNYTSLIHSLIEESQNQQEKNEQEGGC), designated SJ-2176, corresponding to the HIV-1 IIIB gp41 sequence (637-666), inhibited HIV-1 replication, virus-induced cell-cell fusion and cytopathic effects in both CD4+ T and monocytic cell lines. In this study, we show that lengthening the peptide at either the N- or C-terminus enhanced its activity, while shortening the peptide from either end decreased the antiviral activity. Substitution of conserved residues in SJ-2176 by alanines resulted in a decrease or elimination of antiviral activity. Replacement of arginine and lysine in the peptide by glutamines did not diminish antiviral activity and rendered the peptide resistant to trypsin.

During the time course of disulfide bond formation by iodine oxidation (in a methanolic and hydrochloric acid solution) of a cysteinyl(S-acetamidomethyl)-glutaminyl tridecapeptide, we observed by ESI, FAB mass spectrometry (pseudo-molecular ion and ion-fragments) and 1H-NMR a side reaction due to a shift of the Acm leaving group from cysteine to the carboxamide side chain of glutamine. This type of Acm-shift at low level was described previously by L.W. Mendelson et al. (Int. J. Pept. Protein Res. 35:249-257) for an aspariginyl-cysteinyl(S-acetamidomethyl) peptide in an anhydrous hydrochloric solution. We report here the efficiency of glutamine as a scavenger to suppress the S-->N shift of the acetamidomethyl group during S-acetamidomethyl cleavage and sulfhydryl oxidation with iodine, as the folded tridecapeptide was obtained with the expected molecular weight.

The potential polyspecificity of an antipeptide monoclonal antibody was systematically examined using a soluble synthetic combinatorial library (SCL). This SCL was composed of 400 different hexapeptide mixtures, each of which consisted of more than 130,000 peptides totalling 50 million individual sequences in approximately equimolar concentration. The 400 peptide mixtures making up this SCL were screened by competitive enzyme-linked immunosorbent assay (ELISA) for their ability to inhibit monoclonal antibody binding to the original immunizing peptide. Individual peptides were derived from three different peptide mixtures of the peptide library through an iterative screening and selection process. In addition to the identification of the six-residue antigenic determinant recognized by this monoclonal antibody, two other hexapeptides were found to have binding affinities 5- to 10-fold higher than the original antigenic determinant sequence. These peptide sequences represent analogs in which a polar amino acid (threonine) in the original antigenic determinant was substituted with a large, aromatic amino acid (either tryptophan or tyrosine). Peptide analogs of the antigenic determinant, ranging from single to multiple substitutions, as well as peptide sequences completely unrelated to the immunizing peptide, were also identified having binding affinities comparable to the original immunogen. The present study illustrates the power of SCLs for the determination of alternative binding motifs for antigen antibody interactions. The use of SCLs in this manner may help to elucidate the extent of cross-reactivity, polyspecificity and molecular mimicry found in antigen-antibody interactions.

In an attempt to create potent and specific inhibitors of the interaction of thyrotropin (thyroid-stimulating hormone [TSH]) with its receptor, we designed a series of 18 synthetic peptides containing sequences of both alpha and beta subunits that were shown previously to interact with the TSH receptor. These "heteromeric" peptide analogs included amino acid residues from alpha 26-46, beta 31-52, beta 88-95 and beta 101-112 that were arranged variously and were separated from each other by artificial amino acid spacers. Each peptide was tested for its ability to interact with the TSH receptor in a radio-receptor assay (TSH-RRA) using porcine thyroid membranes and a bio-assay for TSH using FRTL-5 cells. Twelve of the 18 peptides showed binding activity in the TSH-RRA. None of the analogs demonstrated thyroid stimulatory activity, but five inhibited TSH bioactivity and were, thus, pure antagonists, the most potent possessing EC50 values in the 3-5 microM range. Specificity of the antagonists was tested by measuring their ability to inhibit hCG binding to ovarian membranes, hCG-stimulated progesterone production in MA-10 rat Leydig tumor cells and FSH binding to testicular membranes. Only those peptides that included the alpha-subunit sequence CFSR or CCFSR exhibited binding activity for the heterologous receptors, and that activity was 10-fold lower than in the TSH assays. None of the heteromeric peptides showed activity in the hCG bioassays, further demonstrating their specificity as TSH antagonists. These studies illustrate the utility of a synthetic peptide approach in the development of analogs of peptide hormones. Future alterations that significantly enhance the potency of these antagonists may result in substances with clinical efficacy in diseases such as Graves' disease and differentiated thyroid cancer that involve the thyrotropin receptor.