Membrane-mediated repulsion between gramicidin pores.

We investigated the X-ray scattering signal of highly aligned multilayers of the zwitterionic lipid 1,2-dilauroyl-sn-glycero-3-phosphatidylcholine containing pores formed by the antimicrobial peptide gramicidin as a function of the peptide/lipid ratio. We are able to obtain information on the structure factor of the pore fluid, which then yields the interaction potential between pores in the plane of the bilayers. Aside from a hard core with a radius close to the geometric radius of the pore, we find a repulsive exponential lipid-mediated interaction with a decay length of 2.5 A and an amplitude that decreases with the pore concentration, in agreement with the hydrophobic matching hypothesis. In dilute systems, the contact value of this interaction is about 30 k(B)T. Similar results are obtained for gramicidin pores inserted within bilayers formed by the nonionic surfactant pentaethylene glycol monododecyl ether.