title: Cation-π interactions as lipid-specific anchors for phosphatidylinositol-specific phospholipase C.
abstract: Amphitropic proteins, such as the virulence factor phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus thuringiensis , often depend on lipid-specific recognition of target membranes. However, the recognition mechanisms for zwitterionic lipids, such as phosphatidylcholine, which is enriched in the outer leaflet of eukaryotic cells, are not well understood. A 500 ns long molecular dynamics simulation of PI-PLC at the surface of a lipid bilayer revealed a strikingly high number of interactions between tyrosines at the interfacial binding site and lipid choline groups with structures characteristic of cation-π interactions. Membrane affinities of PI-PLC tyrosine variants mostly tracked the simulation results, falling into two classes: (i) those with minor losses in affinity, Kd(mutant)/Kd(wild-type) ≤ 5 and (ii) those where the apparent Kd was 50-200 times higher than wild-type. Estimating ΔΔG for these Tyr/PC interactions from the apparent Kd values reveals that the free energy associated with class I is ~1 kcal/mol, comparable to the value predicted by the Wimley-White hydrophobicity scale. In contrast, removal of class II tyrosines has a higher energy cost: ~2.5 kcal/mol toward pure PC vesicles. These higher energies correlate well with the occupancy of the cation-π adducts throughout the MD simulation. Together, these results strongly indicate that PI-PLC interacts with PC headgroups via cation-π interactions with tyrosine residues and suggest that cation-π interactions at the interface may be a mechanism for specific lipid recognition by amphitropic and membrane proteins.
authors.affiliation: Department of Molecular Biology, UniResearch, University of Bergen, Bergen, Norway.
authors.forename: Cédric
authors.initials: C
authors.lastname: Grauffel
authors.forename: Boqian
authors.initials: B
authors.lastname: Yang
authors.forename: Tao
authors.initials: T
authors.lastname: He
authors.forename: Mary F
authors.initials: MF
authors.lastname: Roberts
authors.forename: Anne
authors.initials: A
authors.lastname: Gershenson
authors.forename: Nathalie
authors.initials: N
authors.lastname: Reuter
mesh_terms: D001413:Bacillus thuringiensis / Q000201:enzymology; D004134:Dimyristoylphosphatidylcholine / Q000378:metabolism; D008051:Lipid Bilayers / Q000378:metabolism; D062105:Molecular Docking Simulation; D056004:Molecular Dynamics Simulation; D009154:Mutation; D010716:Phosphatidylinositols / Q000378:metabolism*; D011487:Protein Conformation; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D053835:Unilamellar Liposomes / Q000378:metabolism
chemical_list: D008051:Lipid Bilayers; D010716:Phosphatidylinositols; D053835:Unilamellar Liposomes; D010738:Type C Phospholipases; D004134:Dimyristoylphosphatidylcholine