Barrel-Stave Pore Formation for Four De Novo Designed Antimicrobial Peptides

The interactions of four de novo designed and four natural antimicrobial peptides (AMPs) with supported lipid bilayers (SLBs) were measured and used to gain insight into the mechanism of the four de novo designed AMPs.  These interactions with a Gram-positive bacterial-membrane mimetic SLBs were monitored using a quartz crystal microbalance with dissipation (QCM-D).  Protegrin-1 and indolicidin operated through the same toroidal pore formation mechanism with a SLB comprised of 3:1 mole ratio 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine:1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPC:POPG) lipids.  Magainin-2 inserted into the same SLB with minimal mass addition and caused little SLB disruption, while α-defensin-1 did not measurably interact.  Using these results as references and known mechanisms from the literature for the natural AMPs, the four de novo designed AMPs were found to disrupt the SLB via a 4-stage barrel-stave pore formation mechanism.  The more potent AMPs were able to access further stages of the mechanism at lower AMP doses.  The discovery that the in vitro disruption of bacterial-membrane mimetic SLBs correlated with AMP potency against Mycobacterium tuberculosis cells suggests that this QCM-D method could be used as a relatively fast in vitro screen for AMP efficacy.