natural cyclic peptides
Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract We have found that besides the known cyclolinopeptides A (CLA) and B (CLB), there is a new cyclic peptide in linseed mill cake that we have named CLX. Its composition is very similar to that of CLA, a cyclic peptide with a distinct immunosuppressive activity. The sequence of this peptide has been established as cyclo(PPFFILLX), where X is a non-proteinaceous amino acid, N-methyl-4-aminoproline. This amino acid substitutes for two amino acid residues of CLA, mimicking a dipeptide moiety with a nonplanar cis amide bond. The non-proteinaceous amino acid X may mimic a transition state of the peptide bond which exists in such processes as, e.g., PPIase-catalysed cis/trans amide-Pro bond isomerisation.
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