Characteristic structural features of indolicidin: effects of the cis-trans isomerism on its conformation.

Indolicidin is an antimicrobial peptide showing a broad spectrum of antibacterial and antifungal activities, and according to the cis-trans isomerism of three Xaa-Pro peptide bonds, eight different stereoisomers could be distinguished for this peptide. As the cis-trans isomerism about the Xaa-Pro peptide bonds was not considered in previous studies, the structural features of distinct stereoisomeric forms were not characterized in detail, so far. In this theoretical study, the influences of cis-trans isomerism on the conformation of indolicidin were investigated, as well as the typical structural properties of each stereoisomer were determined, focusing on the secondary structures and intramolecular interactions. Based on the results derived from the molecular dynamics simulations, it could be concluded that the eight different stereoisomeric forms of indolicidin adopted characteristic conformational features. Nevertheless, the appearance of various turn structures and intramolecular interactions proved to be dependent on the cis or trans nature of Xaa-Pro peptide bonds, indicating the relevant role of Pro amino acids in determining the three-dimensional structure of this peptide.