title: Structural and functional analysis of human liver-expressed antimicrobial peptide 2.
abstract: Human liver-expressed antimicrobial peptide 2 (LEAP-2) is a cationic antimicrobial peptide (CAMP) believed to have a protective role against bacterial infection. Little is known about the structure-activity relationships of LEAP-2 or its mechanism of action. In this study we describe the structure of LEAP-2, analyze its interaction with model membranes, and relate them to the antimicrobial activity of the peptide. The structure of LEAP-2, determined by NMR spectroscopy, reveals a compact central core with disorder at the N and C termini. The core comprises a β-hairpin and a 3(10)- helix that are braced by disulfide bonds between Cys17-28 and Cys23-33 and further stabilized by a network of hydrogen bonds. Membrane-affinity studies show that LEAP-2 membrane binding is governed by electrostatic attractions, which are sensitive to ionic strength. Truncation studies show that the C-terminal region of LEAP-2 is irrelevant for membrane binding, whereas the N-terminal (hydrophobic domain) and core regions (cationic domain) are essential. Bacterial-growth-inhibition assays reveal that the antimicrobial activity of LEAP-2 correlates with membrane affinity. Interestingly, the native and reduced forms of LEAP-2 have similar membrane affinity and antimicrobial activities; this suggests that disulfide bonds are not essential for the bactericidal activity. This study reveals that LEAP-2 has a novel fold for a CAMP and suggests that although LEAP-2 exhibits antimicrobial activity under low-salt conditions, there is likely to be another physiological role for the peptide.
authors.affiliation: Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, 4072 Australia.
authors.forename: Sónia Troeira
authors.initials: ST
authors.lastname: Henriques
authors.forename: Chia Chia
authors.initials: CC
authors.lastname: Tan
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Clark
mesh_terms: D000595:Amino Acid Sequence; D000890:Anti-Infective Agents / Q000737:chemistry*; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry*; D001798:Blood Proteins / Q000737:chemistry*; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary
chemical_list: D000890:Anti-Infective Agents; D023181:Antimicrobial Cationic Peptides; D001798:Blood Proteins; D008051:Lipid Bilayers; D010743:Phospholipids; C475606:liver-expressed antimicrobial peptide 2, human