title: Investigations into the ability of the peptide, HAL18, to interact with bacterial membranes.
abstract: Halocidin was isolated from hemocytes, Halocynthia aurantium as a heterodimeric peptide consisting of two alpha-helical subunits, Hal15 and Hal18. Hal18 was shown to have antibacterial properties against Bacillus subtilis (MLC = 15 microM) and Escherichia coli (MLC = 100 microM). The peptide was shown to produce stable monolayers, which were characteristic of alpha-helical peptides predicted to orientate parallel to the surface of the interface. Constant area assays showed that Hal18 was surface active (4 microM) inducing surface pressure changes >30 mN m(-1) characteristic of membrane interactive peptides. The peptide induced stable surface pressure changes in monolayers that were mimetic of B. subtilis membranes (circa 7 mN m(-1)) and E. coli membrane-mimics (circa 4 mN m(-1)). Hal18 inserted readily into zwitterionic DOPE and anionic DOPG monolayers inducing surface pressure changes circa 8 mN m(-1) in both cases, providing evidence that interaction is not headgroup specific. Thermodynamic analysis of compression isotherms showed that the presence of Hal18 destabilised B. subtilis membranes (DeltaG (Mix) > 0), which is in contrast to its stabilising effect on E. coli lipid extract implying the differential antimicrobial efficacy may be driven by lipid packing.
authors.affiliation: Faculty of Science and Technology, University of Central Lancashire, Preston, UK.
authors.forename: Sarah R
authors.initials: SR
authors.lastname: Dennison
authors.forename: Young Soo
authors.initials: YS
authors.lastname: Kim
authors.forename: Hyung Joon
authors.initials: HJ
authors.lastname: Cha
authors.forename: David A
authors.initials: DA
authors.lastname: Phoenix
mesh_terms: D001665:Binding Sites; D002462:Cell Membrane / Q000737:chemistry*; D003198:Computer Simulation; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry*; D011485:Protein Binding
chemical_list: D008051:Lipid Bilayers; D010455:Peptides; D010743:Phospholipids; C460842:halocidin