title: Essential Role of the EF-hand Domain in Targeting Sperm Phospholipase Cζ to Membrane Phosphatidylinositol 4,5-Bisphosphate (PIP2).
abstract: Sperm-specific phospholipase C-ζ (PLCζ) is widely considered to be the physiological stimulus that triggers intracellular Ca(2+) oscillations and egg activation during mammalian fertilization. Although PLCζ is structurally similar to PLCδ1, it lacks a pleckstrin homology domain, and it remains unclear how PLCζ targets its phosphatidylinositol 4,5-bisphosphate (PIP2) membrane substrate. Recently, the PLCδ1 EF-hand domain was shown to bind to anionic phospholipids through a number of cationic residues, suggesting a potential mechanism for how PLCs might interact with their target membranes. Those critical cationic EF-hand residues in PLCδ1 are notably conserved in PLCζ. We investigated the potential role of these conserved cationic residues in PLCζ by generating a series of mutants that sequentially neutralized three positively charged residues (Lys-49, Lys-53, and Arg-57) within the mouse PLCζ EF-hand domain. Microinjection of the PLCζ EF-hand mutants into mouse eggs enabled their Ca(2+) oscillation inducing activities to be compared with wild-type PLCζ. Furthermore, the mutant proteins were purified, and the in vitro PIP2 hydrolysis and binding properties were monitored. Our analysis suggests that PLCζ binds significantly to PIP2, but not to phosphatidic acid or phosphatidylserine, and that sequential reduction of the net positive charge within the first EF-hand domain of PLCζ significantly alters in vivo Ca(2+) oscillation inducing activity and in vitro interaction with PIP2 without affecting its Ca(2+) sensitivity. Our findings are consistent with theoretical predictions provided by a mathematical model that links oocyte Ca(2+) frequency and the binding ability of different PLCζ mutants to PIP2. Moreover, a PLCζ mutant with mutations in the cationic residues within the first EF-hand domain and the XY linker region dramatically reduces the binding of PLCζ to PIP2, leading to complete abolishment of its Ca(2+) oscillation inducing activity.
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and mixosn@yahoo.com.
authors.forename: Michail
authors.initials: M
authors.lastname: Nomikos
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and.
authors.forename: Jessica R
authors.initials: JR
authors.lastname: Sanders
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Parthimos
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and.
authors.forename: Luke
authors.initials: L
authors.lastname: Buntwal
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and.
authors.forename: Brian L
authors.initials: BL
authors.lastname: Calver
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Stamatiadis
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and.
authors.forename: Adrian
authors.initials: A
authors.lastname: Smith
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and.
authors.forename: Matthew
authors.initials: M
authors.lastname: Clue
authors.affiliation: the National Center for Scientific Research "Demokritos," 15310 Aghia Paraskevi, Greece.
authors.forename: Zili
authors.initials: Z
authors.lastname: Sideratou
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and.
authors.forename: Karl
authors.initials: K
authors.lastname: Swann
authors.affiliation: From the Institute of Molecular and Experimental Medicine, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom and lait@cf.ac.uk.
authors.forename: F Anthony
authors.initials: FA
authors.lastname: Lai
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002412:Cations; D002462:Cell Membrane / Q000378:metabolism*; D020832:EF Hand Motifs; D005260:Female; D006868:Hydrolysis; D008081:Liposomes / Q000737:chemistry; D008297:Male; D051379:Mice; D008962:Models, Theoretical; D009154:Mutation; D009865:Oocytes / Q000166:cytology; D010712:Phosphatidic Acids / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D010718:Phosphatidylserines / Q000378:metabolism; D054801:Phosphoinositide Phospholipase C / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D013094:Spermatozoa / Q000201:enzymology*
chemical_list: D002412:Cations; D008081:Liposomes; D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D010718:Phosphatidylserines; D054801:Phosphoinositide Phospholipase C; C499234:Plcz1 protein, mouse; D002118:Calcium
keywords: EF-hand domain; PIP2; calcium intracellular release; fertilization; inositol 1,4,5-trisphosphate; phosphatidylinositol signaling; phospholipase C; sperm