title: Voltage-dependent insertion of alamethicin at phospholipid/water and octane/water interfaces.
abstract: Understanding the binding and insertion of peptides in lipid bilayers is a prerequisite for understanding phenomena such as antimicrobial activity and membrane-protein folding. We describe molecular dynamics simulations of the antimicrobial peptide alamethicin in lipid/water and octane/water environments, taking into account an external electric field to mimic the membrane potential. At cis-positive potentials, alamethicin does not insert into a phospholipid bilayer in 10 ns of simulation, due to the slow dynamics of the peptide and lipids. However, in octane N-terminal insertion occurs at field strengths from 0.33 V/nm and higher, in simulations of up to 100 ns duration. Insertion of alamethicin occurs in two steps, corresponding to desolvation of the Gln7 side chain, and the backbone of Aib10 and Gly11. The proline induced helix kink angle does not change significantly during insertion. Polyalanine and alamethicin form stable helices both when inserted in octane and at the water/octane interface, where they partition in the same location. In water, both polyalanine and alamethicin partially unfold in multiple simulations. We present a detailed analysis of the insertion of alamethicin into the octane slab and the influence of the external field on the peptide structure. Our findings give new insight into the mechanism of channel formation by alamethicin and the structure and dynamics of membrane-associated helices.
authors.affiliation: Laboratory of Molecular Biophysics, Department of Biochemistry, University of Oxford, The Rex Richards Building, South Parks Road, Oxford OX1 3QU, United Kingdom. tieleman@ucalgary.ca
authors.forename: D P
authors.initials: DP
authors.lastname: Tieleman
authors.forename: H J
authors.initials: HJ
authors.lastname: Berendsen
authors.forename: M S
authors.initials: MS
authors.lastname: Sansom
mesh_terms: D000408:Alamethicin / Q000737:chemistry*; D000595:Amino Acid Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D003198:Computer Simulation; D004355:Drug Stability; D004563:Electrochemistry; D008051:Lipid Bilayers / Q000737:chemistry; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009795:Octanes / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D017433:Protein Structure, Secondary; D055672:Static Electricity; D014867:Water
chemical_list: D008051:Lipid Bilayers; D008565:Membrane Proteins; D009795:Octanes; D010455:Peptides; D010713:Phosphatidylcholines; D010743:Phospholipids; D014867:Water; C019529:polyalanine; D000408:Alamethicin; C028694:1-palmitoyl-2-oleoylphosphatidylcholine; C026728:octane