title: A Role for Weak Electrostatic Interactions in Peripheral Membrane Protein Binding.
abstract: Bacillus thuringiensis phosphatidylinositol-specific phospholipase C (BtPI-PLC) is a secreted virulence factor that binds specifically to phosphatidylcholine (PC) bilayers containing negatively charged phospholipids. BtPI-PLC carries a negative net charge and its interfacial binding site has no obvious cluster of basic residues. Continuum electrostatic calculations show that, as expected, nonspecific electrostatic interactions between BtPI-PLC and membranes vary as a function of the fraction of anionic lipids present in the bilayers. Yet they are strikingly weak, with a calculated ΔGel below 1 kcal/mol, largely due to a single lysine (K44). When K44 is mutated to alanine, the equilibrium dissociation constant for small unilamellar vesicles increases more than 50 times (∼2.4 kcal/mol), suggesting that interactions between K44 and lipids are not merely electrostatic. Comparisons of molecular-dynamics simulations performed using different lipid compositions reveal that the bilayer composition does not affect either hydrogen bonds or hydrophobic contacts between the protein interfacial binding site and bilayers. However, the occupancies of cation-π interactions between PC choline headgroups and protein tyrosines vary as a function of PC content. The overall contribution of basic residues to binding affinity is also context dependent and cannot be approximated by a rule-of-thumb value because these residues can contribute to both nonspecific electrostatic and short-range protein-lipid interactions. Additionally, statistics on the distribution of basic amino acids in a data set of membrane-binding domains reveal that weak electrostatics, as observed for BtPI-PLC, might be a less unusual mechanism for peripheral membrane binding than is generally thought.
authors.affiliation: Department of Molecular Biology, University of Bergen, Bergen, Norway; Computational Biology Unit, Department of Informatics, University of Bergen, Bergen, Norway.
authors.forename: Hanif M
authors.initials: HM
authors.lastname: Khan
authors.affiliation: Department of Chemistry, Boston College, Chestnut Hill, Massachusetts.
authors.forename: Tao
authors.initials: T
authors.lastname: He
authors.affiliation: Department of Molecular Biology, University of Bergen, Bergen, Norway; Computational Biology Unit, Department of Informatics, University of Bergen, Bergen, Norway.
authors.forename: Edvin
authors.initials: E
authors.lastname: Fuglebakk
authors.affiliation: Department of Molecular Biology, University of Bergen, Bergen, Norway; Computational Biology Unit, Department of Informatics, University of Bergen, Bergen, Norway.
authors.forename: Cédric
authors.initials: C
authors.lastname: Grauffel
authors.affiliation: Department of Chemistry, Boston College, Chestnut Hill, Massachusetts; Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts.
authors.forename: Boqian
authors.initials: B
authors.lastname: Yang
authors.affiliation: Department of Chemistry, Boston College, Chestnut Hill, Massachusetts.
authors.forename: Mary F
authors.initials: MF
authors.lastname: Roberts
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts.
authors.forename: Anne
authors.initials: A
authors.lastname: Gershenson
authors.affiliation: Department of Molecular Biology, University of Bergen, Bergen, Norway; Computational Biology Unit, Department of Informatics, University of Bergen, Bergen, Norway. Electronic address: nathalie.reuter@uib.no.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Reuter
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D001413:Bacillus thuringiensis / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008565:Membrane Proteins / Q000378:metabolism*; D056004:Molecular Dynamics Simulation; D010715:Phosphatidylglycerols / Q000737:chemistry; D054801:Phosphoinositide Phospholipase C / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D055672:Static Electricity; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D008051:Lipid Bilayers; D008055:Lipids; D008565:Membrane Proteins; D010715:Phosphatidylglycerols; C002773:dimyristoylphosphatidylglycerol; D054801:Phosphoinositide Phospholipase C; D004134:Dimyristoylphosphatidylcholine