title: Stability and membrane interactions of an autotransport protein: MD simulations of the Hia translocator domain in a complex membrane environment.
abstract: Hia is a trimeric autotransporter found in the outer membrane of Haemphilus influenzae. The X-ray structure of Hia translocator domain revealed each monomer to consist of an α-helix connected via a loop to a 4-stranded β-sheet, thus the topology of the trimeric translocator domain is a 12-stranded β-barrel containing 3 α-helices that protrude from the mouth of the β-barrel into the extracellular medium. Molecular dynamics simulations of the Hia monomer and trimer have been employed to explore the interactions between the helices, β-barrel and connecting loops that may contribute to the stability of the trimer. In simulations of the Hia monomer we show that the central α-helix may stabilise the fold of the 4-stranded β-sheet. In simulations of the Hia trimer, a H-bond network involving residues in the β-barrel, α-helices and loops has been identified as providing stability for the trimeric arrangement of the monomers. Glutamine residues located in the loops connecting the α-helices to the β-barrel are orientated in a triangular arrangement such that each forms 2 hydrogen bonds to each of the corresponding glutamines in the other loops. In the absence of the loops, the β-barrel becomes distorted. Simulations show that while the trimeric translocator domain β-barrel is inherently flexible, it is unlikely to accommodate the passenger domain in a folded conformation. Simulations of Hia in an asymmetric model of the outer membrane have revealed membrane-protein interactions that anchor the protein within its native membrane environment.
authors.affiliation: School of Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, UK.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Holdbrook
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Piggot
authors.forename: Mark S P
authors.initials: MS
authors.lastname: Sansom
authors.forename: Syma
authors.initials: S
authors.lastname: Khalid
mesh_terms: D001422:Bacterial Adhesion; D018988:Bacterial Translocation; D001703:Biophysics / Q000379:methods; D002462:Cell Membrane / Q000378:metabolism*; D003198:Computer Simulation; D018360:Crystallography, X-Ray / Q000379:methods; D019281:Dimerization; D006193:Haemophilus influenzae / Q000378:metabolism*; D008055:Lipids / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D055672:Static Electricity; D013997:Time Factors; D014965:X-Rays
chemical_list: D008055:Lipids