title: Myo-inositol monophosphatase is an activated target of calbindin D28k.
abstract: Calbindin D(28k) (calbindin) is a member of the calmodulin superfamily of Ca(2+)-binding proteins. An intracellular target of calbindin was discovered using bacteriophage display. Human recombinant calbindin was immobilized on magnetic beads and used in affinity purification of phage-displayed peptides from a random 12-mer peptide library. One sequence, SYSSIAKYPSHS, was strongly selected both in the presence of Mg(2+) and in the presence of Ca(2+). Homology search against the protein sequence data base identified a closely similar sequence, ISSIKEKYPSHS, at residues 55-66 in myo-inositol-1(or 4)-monophosphatase (IMPase, EC ), which constitute a strongly conserved and exposed region in the three-dimensional structure. IMPase is a key enzyme in the regulation of the activity of the phosphatidylinositol-signaling pathway. It catalyzes the hydrolysis of myo-inositol-1(or 4)-monophosphate to form free myo-inositol, maintaining a supply that represents the precursor for inositol phospholipid second messenger signaling systems. Fluorescence spectroscopy showed that isolated calbindin and IMPase interact with an apparent equilibrium dissociation constant, K(D), of 0.9 microm. Both apo and Ca(2+)-bound calbindin was found to activate IMPase up to 250-fold, depending on the pH and substrate concentration. The activation is most pronounced at conditions that otherwise lead to a very low activity of IMPase, i.e. at reduced pH and at low substrate concentration.
authors.affiliation: Department of Biophysical Chemistry, Lund University, Chemical Centre, P.O. Box 124, Sweden.
authors.forename: Tord
authors.initials: T
authors.lastname: Berggard
authors.forename: Olga
authors.initials: O
authors.lastname: Szczepankiewicz
authors.forename: Eva
authors.initials: E
authors.lastname: Thulin
authors.forename: Sara
authors.initials: S
authors.lastname: Linse
mesh_terms: D000595:Amino Acid Sequence; D064092:Calbindin 1; D064026:Calbindins; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007295:Inositol Phosphates / Q000378:metabolism*; D008969:Molecular Sequence Data; D019151:Peptide Library; D010716:Phosphatidylinositols / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry / Q000378:metabolism*; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*
chemical_list: C576498:CALB1 protein, human; D064092:Calbindin 1; D064026:Calbindins; D007295:Inositol Phosphates; D019151:Peptide Library; D010716:Phosphatidylinositols; D064030:S100 Calcium Binding Protein G; C002647:inositol 1-phosphate; C045537:inositol 4-phosphate; D010744:Phosphoric Monoester Hydrolases; C021822:myo-inositol-1 (or 4)-monophosphatase; D002118:Calcium