We performed microsecond long coarse-grained molecular dynamics simulations to elucidate the lateral structure and domain dynamics of a phosphatidylethanolamine (PE)/phosphatidylglycerol (PG) mixed bilayer (7/3), mimicking the inner membrane of gram-negative bacteria. Specifically, we address the effect of surface bound antimicrobial peptides (AMPs) on the lateral organization of the membrane. We find that, in the absence of the peptides, the minor PG fraction only forms small clusters, but that these clusters grow in size upon binding of the cationic AMPs. The presence of AMPs systematically affects the dynamics and induces long-range order in the structure of PG domains, stabilizing the separation between the two lipid fractions. Our results help in understanding the initial stages of destabilization of cytoplasmic bacterial membranes below the critical peptide concentration necessary for disruption, and provide a possible explanation for the multimodal character of AMP activity. © 2010 American Chemical Society.