title: Identification and characterization of calmodulin-binding proteins in mammalian sperm flagella.
abstract: A calcium and calmodulin-regulated cyclic nucleotide phosphodiesterase has been shown to be an integral component of both rat and bovine sperm flagella. The calcium-activated enzyme was inhibited by both trifluoperazine (ID50 = 10 microM) and [ethylene-bis(oxyethylenenitrilo)]tetraacetic acid (EGTA), and the basal activity measured in the presence of EGTA was stimulated by limited proteolysis to that observed in the presence of calcium/calmodulin. 125I-Calmodulin binding to purified rat sperm flagella has been characterized and the flagellar-associated calmodulin-binding proteins identified by a combination of gel and nitrocellulose overlay procedures and by chemical cross-linking experiments using dimethyl suberimidate. 125I-Calmodulin bound to demembranated rat sperm flagella in a time- and concentration-dependent manner. At equilibrium, 30-40% of the bound 125I-calmodulin remains associated with the flagella after treatment with EGTA or trifluoperazine. The majority of the bound 125I-calmodulin, both the Ca2+-dependent and -independent, was displaced by excess calmodulin. A 67-kDa calmodulin-binding protein was identified by both the gel and nitrocellulose overlay procedures. In both cases, binding was dependent on Ca2+ and was totally inhibited by trifluoperazine, EGTA, and excess calmodulin. On nitrocellulose overlays, the concentration of calmodulin required to decrease binding of 125I-calmodulin by 50% was between 10(-10) and 10(-11) M. Limited proteolysis resulted in the total loss of all Ca2+-dependent binding to the 67-kDa polypeptide. Chemical cross-linking experiments identified a major calcium-dependent 125I-calmodulin:polypeptide complex in the 84-90-kDa molecular mass range and a minor complex of approximately 200 kDa. Immunoblot analysis showed that the major 67-kDa calmodulin-binding protein did not cross-react with polyclonal antibodies raised against either the calcium/calmodulin-regulated cyclic nucleotide phosphodiesterase or phosphoprotein phosphatase (calcineurin) from bovine brain.
authors.affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: W M
authors.initials: WM
authors.lastname: Wasco
authors.forename: R L
authors.initials: RL
authors.lastname: Kincaid
authors.forename: G A
authors.initials: GA
authors.lastname: Orr
mesh_terms: D015087:2',3'-Cyclic-Nucleotide Phosphodiesterases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000502:physiology; D002147:Calmodulin / Q000378:metabolism / Q000502:physiology; D002148:Calmodulin-Binding Proteins / Q000032:analysis*; D002417:Cattle; D003101:Collodion; D003432:Cross-Linking Reagents; D004533:Egtazic Acid; D006868:Hydrolysis; D008297:Male; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D013082:Sperm Tail / Q000032:analysis* / Q000378:metabolism; D013094:Spermatozoa / Q000032:analysis*; D014268:Trifluoperazine; D014357:Trypsin
chemical_list: D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D003432:Cross-Linking Reagents; D014268:Trifluoperazine; D004533:Egtazic Acid; D003101:Collodion; D015087:2',3'-Cyclic-Nucleotide Phosphodiesterases; D014357:Trypsin; D002118:Calcium