title: Competition between anion binding and dimerization modulates Staphylococcus aureus phosphatidylinositol-specific phospholipase C enzymatic activity.
abstract: BACKGROUND
  Bacterial phosphatidylinositol-specific phospholipase C targets PI and glycosylphosphatidylinositol-linked proteins of eukaryotic cells.
  
  
  RESULTS
  Functional relevance of a homodimeric S. aureus PI-PLC crystal structure is supported by enzyme kinetics and mutagenesis. Nonsubstrate phosphatidylcholine increases activity by facilitating enzyme dimerization.
  
  
  CONCLUSIONS
  Activating transient dimerization is antagonized by anions binding to a discrete site.
  
  
  CONCLUSIONS
  Interplay of protein oligomerization and anion binding controls enzyme activity. Staphylococcus aureus phosphatidylinositol-specific phospholipase C (PI-PLC) is a secreted virulence factor for this pathogenic bacterium. A novel crystal structure shows that this PI-PLC can form a dimer via helix B, a structural feature present in all secreted, bacterial PI-PLCs that is important for membrane binding. Despite the small size of this interface, it is critical for optimal enzyme activity. Kinetic evidence, increased enzyme specific activity with increasing enzyme concentration, supports a mechanism where the PI-PLC dimerization is enhanced in membranes containing phosphatidylcholine (PC). Mutagenesis of key residues confirm that the zwitterionic phospholipid acts not by specific binding to the protein, but rather by reducing anionic lipid interactions with a cationic pocket on the surface of the S. aureus enzyme that stabilizes monomeric protein. Despite its structural and sequence similarity to PI-PLCs from other Gram-positive pathogenic bacteria, S. aureus PI-PLC appears to have a unique mechanism where enzyme activity is modulated by competition between binding of soluble anions or anionic lipids to the cationic sensor and transient dimerization on the membrane.
authors.affiliation: Department of Chemistry, Boston College, Chestnut Hill, MA 02467, USA.
authors.forename: Jiongjia
authors.initials: J
authors.lastname: Cheng
authors.forename: Rebecca
authors.initials: R
authors.lastname: Goldstein
authors.forename: Boguslaw
authors.initials: B
authors.lastname: Stec
authors.forename: Anne
authors.initials: A
authors.lastname: Gershenson
authors.forename: Mary F
authors.initials: MF
authors.lastname: Roberts
mesh_terms: D000838:Anions / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D019281:Dimerization; D007700:Kinetics; D054801:Phosphoinositide Phospholipase C / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D013211:Staphylococcus aureus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D013379:Substrate Specificity
chemical_list: D000838:Anions; D001426:Bacterial Proteins; D054801:Phosphoinositide Phospholipase C