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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1972 Jul;69(7):1825–1829. doi: 10.1073/pnas.69.7.1825

Conformational Interconversions of the Cyclic Hexapeptide Cyclo(Pro-Gly)3*,†

Charles M Deber 1, Dennis A Torchia ‡,‡, Simon C K Wong 1, Elkan R Blout 1
PMCID: PMC426811  PMID: 4505660

Abstract

A cyclic hexapeptide, cyclo(Pro-Gly-Pro-Gly-Pro-Gly), has been synthesized; its solution conformations were examined by 220-MHz nuclear magnetic resonance spectroscopy. The solution structures have been deduced, and shown to vary as a function of solvent polarity. In addition, it has been found that this cyclic peptide binds alkali metal cations. While the predominant conformation of this cyclic peptide is 3-fold symmetric in the apolar solvent methylene chloride, an asymmetric structure is preferred in some polar solvents (water, dimethylsulfoxide). However, addition of alkali metal salts, such as sodium thiocyanate, to dimethylsulfoxide solutions of the peptide shifts the conformational equilibrium in favor of a second type of C3-symmetric structure, presumably the result of the formation of a stable peptide-metal ion complex. Nuclear magnetic resonance data suggest that the peptide in methylene chloride solution takes up a conformation containing three cis′ Pro Cα-C=O bonds and three cis Gly-Pro peptide bonds; that water and dimethylsulfoxide stabilize a conformer in which one (or two) sets of such bonds of a given Pro-Gly unit have undergone interconversion to trans′/trans forms; and that alkali metal cations complex the cyclic peptide in a C3-symmetric all-trans′/trans structure.

Keywords: peptides, NMR, alkali metal complexes

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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