Crystallization of the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum. Inhibition by myotoxin a.
Decavanadate produces extensive ordered arrays of Ca2+-ATPase molecules on sarcoplasmic reticulum (SR) vesicle surfaces [(1984) J. Bioenerg. Biomembranes 16, 491-505] and the basic unit of these crystalline structures seems to be a dimer of Ca2+-ATPase [(1983) J. Ultrastruct. Res. 24, 454-464; (1984) J. Mol. Biol. 174, 193-204]. Myotoxin a, isolated from the venom of the prairie rattlesnake Crotalus viridis viridis, is a muscle-degenerating polypeptide and its primary site of interaction is the SR membrane, where it uncouples CA2+-translocation from CA2+-dependent ATP hydrolysis [(1986) Arch. Biochem. Biophys. 246, 90-97]. The effect of myotoxin a on decavanadate-induced two-dimensional Ca2+-ATPase crystals of SR membranes has been investigated. The toxin inhibits the formation of two-dimensional SR-membrane crystals and disrupts previously formed crystals in a time- and concentration-dependent manner, which parallels the uncoupling of ATP hydrolysis from Ca2+ translocation. Two-dimensional crystalline arrays of the SR membrane have a typical diffraction pattern which, after myotoxin a treatment, displays a progressive loss of order. Decavanadate is an uncompetitive inhibitor of the Ca2+-ATPase enzyme-myotoxin a complex. The present results suggest that a Ca2+-ATPase dimer is required for coupling Ca2+ translocation to Ca2+-dependent ATP hydrolysis.
D000818:Animals; D000252:Calcium-Transporting ATPases; D003435:Crotalid Venoms / Q000494:pharmacology*; D003460:Crystallization; D008081:Liposomes; D009132:Muscles / Q000201:enzymology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014638:Vanadates / Q000494:pharmacology
D003435:Crotalid Venoms; D008081:Liposomes; D014638:Vanadates; C018932:myotoxin A; D000252:Calcium-Transporting ATPases