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Using a molecular modeling method, different conformations of surfactin at a hydrophobic/hydrophilic interface are established. Two conformations of the peptide ring (S1 and S2) provided by NMR experiments built with three different aliphatic chains in folded or extended configurations were studied. For the structures including the S2 peptide ring conformation, the theoretical interfacial molecular area corresponds to the experimental limiting area A 0 value obtained with a Langmuir film balance. The peptide ring is positioned in the plane of the interface with the two acidic chains close to each other and protruding in the aqueous phase, and the β-hydroxy fatty acid chain, folded to interact mainly with the Leu2 side chain and also with the Val4 side chain. This design has the largest calculated molecular area and would correspond to the most stable amphipathic structure representing the surfactin experimental behavior in weak compression.

Modeling analysis was used to understand the molecular mechanisms of the biological activities of surfactin, in particular, its hemolytic activity. This study highlights the importance of the fatty acid chain hydrophobicity of the surfactin on its activities, the C15 homologue being the most active. This is related to its self-association capacity. The detergent effect is the predominant mechanism involved in the hemolytic activity. A two-step mechanism is suggested, depending on the surfactin concentration. Other mechanisms (cationic channel, mobile carrier) can also be involved in particular conditions.