Competition between Anion Binding and Dimerization Modulates Staphylococcus aureus Phosphatidylinositol-specific Phospholipase C Enzymatic Activity |
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Authors: | Jiongjia Cheng Rebecca Goldstein Boguslaw Stec Anne Gershenson Mary F Roberts |
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Institution: | From the ‡Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467.;the §Sanford-Burnham Medical Research Institute, La Jolla, California 92037, and ;the ¶Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003 |
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Abstract: | 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. |
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Keywords: | Crystal Structure Fluorescence Correlation Spectroscopy Kinetics Lipolysis Membrane Enzymes Phosphatidylinositol Phospholipase C |
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