Channel structures in synthetic polypeptides with alternating configurations. Conformational analysis of poly(DL-proline).

Theoretical conformational analysis of L,D alternating sequences of poly alpha-amino acids is reported in connection with the ability of naturally occurring peptide and depsipeptide having alternating configurations to increase selectively the ion permeability across membranes. The most stable structures of poly(DL-proline), of which the conformational variability is practically limited to the choice between cis and trans conformations of the peptide bonds, were characterized. The all-trans conformation results in a flat helical structure possessing the main features for acting as an ion channel across membranes as actually found experimentally. Random cis-trans conformational sequences provide an alternative mechanism of ion transport intermediate between the ion channel and the ion carrier.