title: Structure-activity relationships for the beta-hairpin cationic antimicrobial peptide polyphemusin I.
abstract: The solution structure of polyphemusin I was determined using (1)H-NMR spectroscopy. Polyphemusin I was found to be an amphipathic, beta-hairpin connected by a type I' beta-turn. The 17 low-energy structures aligned very well over the beta-sheet region while both termini were poorly defined due in part to a hinge-like region centred in the molecule about arginine residues 6 and 16. Conversely, a linear analogue, PM1-S, with all cysteines simultaneously replaced with serine was found to be dynamic in nature, and a lack of medium and long-range NOEs indicated that this molecule displayed no favoured conformation. Circular dichroism (CD) spectroscopy confirmed that in solution, 50% trifluoroethanol (TFE) and in the presence of liposomes, PM1-S remained unstructured. The antimicrobial activity of PM1-S was found to be 4- to 16-fold less than that of polyphemusin I and corresponded with a 4-fold reduction in bacterial membrane depolarization. Both peptides were able to associate with lipid bilayers in a similar fashion; however, PM1-S was completely unable to translocate model membranes while polyphemusin I retained this activity. It was concluded that the disulfide-constrained, beta-sheet structure of polyphemusin I is required for maximum antimicrobial activity. Disruption of this structure results in reduced antimicrobial activity and completely abolishes membrane translocation indicating that the linear PM1-S acts through a different antimicrobial mechanism.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, #300-6174 University Boulevard, Vancouver, British Columbia, V6T 1Z3, Canada.
authors.forename: Jon-Paul S
authors.initials: JP
authors.lastname: Powers
authors.forename: Annett
authors.initials: A
authors.lastname: Rozek
authors.forename: Robert E W
authors.initials: RE
authors.lastname: Hancock
mesh_terms: D019943:Amino Acid Substitution; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002942:Circular Dichroism; D003545:Cysteine / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D010455:Peptides; D021381:Protein Transport; D012694:Serine / Q000378:metabolism; D013329:Structure-Activity Relationship; D013997:Time Factors
chemical_list: D023181:Antimicrobial Cationic Peptides; D010455:Peptides; C062385:polyphemusin I; D012694:Serine; D003545:Cysteine