title: A novel plasma membrane Ca(2+)-pump inhibitor: caloxin 1A1.
abstract: The plasma membrane Ca(2+)-Mg(2+)-ATPase is a Ca(2+)-pump that expels Ca2+ from cells. Here we report caloxin 1A1-a novel peptide inhibitor (Ki=100 microM) of plasma membrane Ca(2+)-pump-obtained by screening a cysteine bridge-constrained random peptide library for binding to the first extracellular domain of plasma membrane Ca(2+)-pump. Dithiothreitol removed the inhibition indicating that the constraint imposed by the cysteine bridge is required for the inhibition. Caloxin 1A1 also inhibited the fast twitch sarcoplasmic reticulum Ca(2+)-Mg(2+)-ATPase although weakly. Glutathione dimers (containing a cysteine bridge) inhibited the Ca(2+)-Mg(2+)-ATPase activity of sarcoplasmic reticulum Ca(2+)-Mg(2+)-ATPase, but not that of plasma membrane Ca(2+)-pump. Caloxin 1A1 stabilised Ca(2+)-dependent formation of the acid stable 140-kDa acylphosphate which is a partial reaction of this enzyme. Thus caloxin 1A1 inhibits the plasma membrane Ca(2+)-pump by perturbing the first extracellular domain indicating that the transmembrane domains 1 and 2 play a role in its reaction cycle. This finding is consistent with rearrangements that occur in transmembrane helices 1 and 2 during reaction cycle of sarcoplasmic reticulum Ca(2+)-pump. Caloxin 1A1 caused an increase in cytosolic Ca2+ concentration in endothelial cells.
authors.affiliation: Department of Biology, McMaster University, Hamilton, Ontario, Canada L8N 3Z5.
authors.forename: Jyoti
authors.initials: J
authors.lastname: Pande
authors.forename: Kanwaldeep K
authors.initials: KK
authors.lastname: Mallhi
authors.forename: Ashok K
authors.initials: AK
authors.lastname: Grover
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000201:enzymology; D005978:Glutathione / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*; D008969:Molecular Sequence Data; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology; D013552:Swine
chemical_list: D008565:Membrane Proteins; D019151:Peptide Library; D010455:Peptides; D010710:Phosphates; C501980:caloxin 1A1; D017301:Ca(2+) Mg(2+)-ATPase; D005978:Glutathione; D002118:Calcium; D004229:Dithiothreitol