title: Characterization of a membrane protein from brain mediating the inhibition of inositol 1,4,5-trisphosphate receptor binding by calcium.
abstract: Inositol 1,4,5-trisphosphate (InsP3) is a component of the phosphoinositide second-messenger system which mobilizes Ca2+ from intracellular stores. Recently, an InsP3 receptor binding protein from rat cerebellar membranes was solubilized and purified to homogeneity. The potent inhibition by Ca2+ of [3H]InsP3 binding to the InsP3 receptor in cellular membranes is not apparent in the purified receptor. The Ca2+-dependent inhibition of [3H]InsP3 binding in the crude homogenate (concn. giving 50% inhibition = 300 nM) can be restored by addition of solubilized cerebellar membranes to the purified receptor. In the present study, we further characterize the protein in solubilized membranes which confers Ca2+-sensitivity to the receptor, and which we term 'calmedin'. Calmedin appears to be a neutral membrane protein with an estimated Mr of 300,000 by gel filtration in the presence of Triton X-100. Calmedin confers a Ca2+-sensitivity to InsP3 receptor binding, which can be completely reversed by 10 min incubation with EDTA and therefore does not represent Ca2+-dependent proteinase action. Calmedin effects on the purified InsP3 receptor depend on Ca2+ binding to the calmedin, although Ca2+ also binds directly to the InsP3 receptor. The regional distribution of calmedin differs from that of the InsP3 receptor in the brain, suggesting that it also mediates other Ca2+-dependent functions. Calmedin activity in peripheral tissues is much lower than in brain.
authors.affiliation: Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
authors.forename: S K
authors.initials: SK
authors.lastname: Danoff
authors.forename: S
authors.initials: S
authors.lastname: Supattapone
authors.forename: S H
authors.initials: SH
authors.lastname: Snyder
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D015220:Calcium Channels; D002850:Chromatography, Gel; D004492:Edetic Acid / Q000494:pharmacology; D006493:Heparin / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000187:drug effects*; D018160:Receptors, Cytoplasmic and Nuclear; D014018:Tissue Distribution
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007295:Inositol Phosphates; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; C057753:calmedin; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; D004492:Edetic Acid; D002118:Calcium