title: Evidence for a global inhibitor-induced conformation change on the Ca(2+)-ATPase of sarcoplasmic reticulum from paired inhibitor studies.
abstract: The Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum is inhibited by a variety of hydrophobic, hydroxy-containing molecules. A kinetic method has been used to study competition between binding of pairs of inhibitors to the ATPase. The presence of 2,5-di-tert-butyl-1,4-dihydroxybenzene (BHQ) decreases the affinity of the ATPase for 2,5-dipropyl-1,4-dihydroxybenzene (PHQ), suggesting that PHQ and BHQ bind to the same site on the ATPase. In contrast, the presence of BHQ increases the affinity of the ATPase for curcumin and vice versa. This suggests that BHQ and curcumin bind to separate sites on the ATPase and that binding of the first inhibitor to the ATPase results in a change to a conformation with higher affinity for the second inhibitor. This is consistent with previous experiments with BHQ and thapsigargin suggesting a conformation change on inhibitor binding, E2 + I <--> 2; E2I <--> 2; E2(A)I, with E2(A)I having a higher affinity for the second inhibitor than E2. The affinity for BHQ is also increased by binding of diethylstilbesterol, ellagic acid, or nonylphenol, and the affinity for curcumin is also increased by ellagic acid. These results showing that binding of a variety of inhibitors of very different structures all result in a general increase in inhibitor affinity point to a global conformational change on the Ca(2+)-ATPase caused by inhibitor binding, as well as any local, inhibitor-specific changes in conformation.
authors.affiliation: Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Southampton SO16 7PX, U.K.
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Logan-Smith
authors.forename: J Malcolm
authors.initials: JM
authors.lastname: East
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Lee
mesh_terms: D001667:Binding, Competitive; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D015394:Molecular Structure; D018482:Muscle, Skeletal / Q000201:enzymology; D011487:Protein Conformation; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D004791:Enzyme Inhibitors; D000252:Calcium-Transporting ATPases