title: Structure of the S. aureus PI-specific phospholipase C reveals modulation of active site access by a titratable π-cation latched loop.
abstract: Staphylococcus aureus secretes a phosphatidylinositol-specific phospholipase C (PI-PLC) as a virulence factor that is unusual in exhibiting higher activity at acidic pH values than other enzymes in this class. We have determined the crystal structure of this enzyme at pH 4.6 and pH 7.5. Under slightly basic conditions, the S. aureus PI-PLC structure closely follows the conformation of other bacterial PI-PLCs. However, when crystallized under acidic conditions, a large section of mobile loop at the αβ-barrel rim in the vicinity of the active site shows ~10 Å shift. This loop displacement at acidic pH is the result of a titratable intramolecular π-cation interaction between His258 and Phe249. This was verified by a structure of the mutant protein H258Y crystallized at pH 4.6, which does not exhibit the large loop shift. The intramolecular π-cation interaction for S. aureus PI-PLC provides an explanation for the activity of the enzyme at acid pH and also suggests how phosphatidylcholine, as a competitor for Phe249, may kinetically activate this enzyme.
authors.affiliation: Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467, United States.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Goldstein
authors.forename: Jiongjia
authors.initials: J
authors.lastname: Cheng
authors.forename: Boguslaw
authors.initials: B
authors.lastname: Stec
authors.forename: Mary F
authors.initials: MF
authors.lastname: Roberts
mesh_terms: D020134:Catalytic Domain; D006863:Hydrogen-Ion Concentration; D007295:Inositol Phosphates / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D054801:Phosphoinositide Phospholipase C / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012995:Solubility; D013203:Staphylococcal Infections / Q000378:metabolism; D013211:Staphylococcus aureus / Q000201:enzymology* / Q000472:pathogenicity; D013379:Substrate Specificity; D014867:Water / Q000737:chemistry
chemical_list: D007295:Inositol Phosphates; D014867:Water; C010199:inositol cyclic phosphate; D054801:Phosphoinositide Phospholipase C