Distinct membrane interaction mechanisms of gramicidin A and S in mammalian cells: A combined experimental and molecular dynamics study.

Gramicidins, a class of ionophores, with a well-known antimicrobial activity against bacteria, and more recently against cancer cells, present two distinct structure types: linear peptides for Gramicidin A, B and C and cyclic peptide for Gramicidin S. Independent of their structure, the first stage of their action mechanism involves their interaction with the plasma membrane of the cells. Considering this, we were interested to study how the peptide structure affects cell properties (cell viability, LDH release, etc) and how it correlates with membrane fluidity parameters (GP , ΔSr, Rs) and molecular simulation parameters (APL, bilayer thickness, and GA membrane permeation). We demonstrated different action mechanisms for the two Gramicidins when applied to mammalian cells: a decrease in cell viability and an increase in LDH release, which correlate well with changes at the plasma membrane level. Both peptides induce a decrease in local membrane fluidity, and the measurements were able to distinguish between the responses elicited by the two peptides. Molecular simulation suggests that lipids are more closely packed in the proximity of the GA pore compared to GS, supporting the experimental observation.