1. Effect of conformation on the conversion of cyclo-(1,7)-Gly-Arg-Gly-Asp-Ser-Pro-Asp-Gly-OH to its cyclic imide degradation product
S J Bogdanowich-Knipp, S D Jois, T J Siahaan J Pept Res. 1999 Jul;54(1):43-53. doi: 10.1034/j.1399-3011.1999.00091.x.
The objective of this study was to explain the increased propensity for the conversion of cyclo-(1,7)-Gly-Arg-Gly-Asp-Ser-Pro-Asp-Gly-OH (1), a vitronectin-selective inhibitor, to its cyclic imide counterpart cyclo-(1,7)-Gly-Arg-Gly-Asu-Ser-Pro-Asp-Gly-OH (2). Therefore, we present the conformational analysis of peptides 1 and 2 by NMR and molecular dynamic simulations (MD). Several different NMR experiments, including COSY, COSY-Relay, HOHAHA, NOESY, ROESY, DQF-COSY and HMQC, were used to: (a) identify each proton in the peptides; (b) determine the sequential assignments; (c) determine the cis-trans isomerization of X-Pro peptide bond; and (d) measure the NH-HCalpha coupling constants. NOE- or ROE-constraints were used in the MD simulations and energy minimizations to determine the preferred conformations of cyclic peptides 1 and 2. Both cyclic peptides 1 and 2 have a stable solution conformation; MD simulations suggest that cyclic peptide 1 has a distorted type I beta-turn at Arg2-Gly3-Asp4-Ser5 and cyclic peptide 2 has a pseudo-type I beta-turn at Ser5-Pro6-Asp7-Gly1. A shift in position of the type I beta-turn at Arg2-Gly3-Asp4-Ser5 in peptide 1 to Ser5-Pro6-Asp7-Gly1 in peptide 2 occurs upon formation of the cyclic imide at the Asp4 residue. Although the secondary structure of cyclic peptide 1 is not conducive to succinimide formation, the reaction proceeds via neighbouring group catalysis by the Ser5 side chain. This mechanism is also supported by the intramolecular hydrogen bond network between the hydroxyl side chain and the backbone nitrogen of Ser5. Based on these results, the stability of Asp-containing peptides cannot be predicted by conformational analysis alone; the influence of anchimeric assistance by surrounding residues must also be considered.
2. Functional peptide-polyurethane conjugates with extended circulatory half-lives
J A Braatz, Y Yasuda, K Olden, K M Yamada, A H Heifetz Bioconjug Chem. 1993 Jul-Aug;4(4):262-7. doi: 10.1021/bc00022a003.
Peptides containing the RGD sequence were covalently attached to an isocyanate-containing polyurethane prepolymer and the biological properties of the complexes were evaluated. For the pentapeptide H2N-Tyr-Arg-Gly-Asp-Ser-OH (single-letter code, YRGDS), polymer conjugation lead to an increased half-life in the blood circulation of mice to > 10 h. The effect of covalent attachment of polymer on biological activity was examined in a related peptide, H2N-Gly-Arg-Gly-Asp-Ser-Pro-Ala-Cys- OH (GRGDSPAC). Inhibition of B16-F10 melanoma cell attachment and spreading on plates coated with fibronectin by an RGD-containing peptide and polymer-conjugated GRGDSPAC was observed to occur at similar concentrations. We conclude that the conjugation of peptides containing the Arg-Gly-Asp motif to this polymer resolves previous problems of their rapid loss from the circulation, while still allowing retention of full biological inhibitory activity.
3. Modulation of vitronectin receptor-mediated osteoclast adhesion by Arg-Gly-Asp peptide analogs: a structure-function analysis
M A Horton, E L Dorey, S A Nesbitt, J Samanen, F E Ali, J M Stadel, A Nichols, R Greig, M H Helfrich J Bone Miner Res. 1993 Feb;8(2):239-47. doi: 10.1002/jbmr.5650080215.
This study details the investigation of induction of retractile shape change in the osteoclast through inhibition of adhesion between osteoclasts and matrix with (1) peptide analogs bearing an Arg-Gly-Asp (RGD) sequence, (2) antibodies to the integrin alpha V beta 3 vitronectin receptor, and (3) the RGD-containing snake venom peptide echistatin. Osteoclast retraction on dentin has been demonstrated for GRGDSP peptide, in contrast to the inactivity of the analog containing the conservative RGE sequence modification. An osteoclast adhesion assay employing rat or chick bone cells and serum-coated glass coverslips as substrate was developed for routine evaluation of inhibition of adhesion. Antibodies F4 and F11 to the beta 3 chain of rat vitronectin receptor were effective at submicromolar concentrations in rat osteoclasts (IC50 0.29 and 0.05 microM, respectively), whereas MAb 23C6 to human/chick vitronectin receptor was somewhat less effective against chick osteoclasts (IC50 1.6 microM). A rank order of RGD analog activity (mean IC50, microM) in the serum-coated glass adhesion assay was derived for the linear peptides GRGDSP (201 microM), GRGDTP (180 microM), Ac-RGDS-NH2 (84 microM), Ac-RGDV-NH2 (68 microM), RGDV (43 microM), GRGDS (38 microM), and RGDS (26 microM). The two most potent short peptides were the cyclic analog SK&F 106760 Ac-S,S-cyclo-(Cys-(N alpha Me)Arg-Gly-Asp-Pen)-NH2 (IC50 7.0 microM), and the Telios peptide H-Gly-S,S-cyclo-(Pen-Gly-Arg-Gly-Asp-Ser-Pro-Cys)-Ala-OH (IC50 6.6 microM). The snake venom peptide echistatin was the most potent substance evaluated in the serum-coated glass assay (IC50 0.78 nM) employing either rat or chick osteoclasts.(ABSTRACT TRUNCATED AT 250 WORDS)
