X-PRO PEPTIDE-BOND AS AN NMR PROBE FOR CONFORMATIONAL STUDIES OF FLEXIBLE LINEAR PEPTIDES

The equilibrium between the cis and trans forms of X-Pro peptide bonds can be measured in the 13NMR spectra. This study investigates how observation of this equilibrium could be used as an NMR probe for conformational studies of flexible polypeptide chains. The experiments include studies by 13CNMR of a series of linear oligopeptides containing different X-L-Pro peptide bonds, with X = Gly, L-Ala, L-Leu, L-Phe, D-Ala, D-Leu and D-Phe. X-Pro peptide bonds can generally be useful as 13CNMR probes reporting the formation of nonrandom conformations in flexible polypeptide chains. The cis-trans equilibrium of X-Pro is greatly affected by the side chain of X and the configuration of the .alpha.-carbon atom of X. Some general rules are suggested for practical applications of the X-Pro NMR probes in conformational studies of polypeptide chains.