title: A new multigene family encoding calcium-dependent calmodulin-binding membrane proteins of Paramecium tetraurelia.
abstract: Ca2+/calmodulin (CaM) regulates various physiological processes in a wide variety of organisms, metazoa and protists alike. To better understand Ca2+/CaM-dependent processes, particularly those with membrane-associated components, we studied Ca2+/CaM-binding membrane proteins in Paramecium tetraurelia, a unicellular model system. A CaM-binding protein, PCM1 (Paramecium CaM-binding membrane-bound protein), from a detergent-solubilized ciliary membrane fraction was identified and purified through Ca2+-dependent CaM-affinity chromatography. PCM1 has an apparent molecular mass of approx. 65kDa. It binds radiolabeled CaM in blot overlay assays and binds to CaM-affinity columns, both only in the presence of 10 microM or higher Ca2+. Three peptide sequences from PCM1 were obtained, and polymerase chain reaction (PCR) and Southern hybridization experiments were designed accordingly, leading to a partial cDNA clone for PCM1 and the discovery of three homologs: PCM2, PCM3 and PCM4. Amino acid sequences predicted by the full-length coding sequence for PCM3 and partial genes for PCM1, PCM2 and PCM4 are very similar (approx. 85% amino-acid identities). Their sequences indicate that they are hitherto novel proteins with beta/gamma-crystallin domains, cysteine-rich regions and potential CaM-binding domains. These protein motifs are suggested to mediate protein-protein interaction important for Ca2+/CaM signal transduction event(s) through the PCM family of proteins.
authors.affiliation: Laboratory of Molecular Biology, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: C W
authors.initials: CW
authors.lastname: Chan
authors.forename: Y
authors.initials: Y
authors.lastname: Saimi
authors.forename: C
authors.initials: C
authors.lastname: Kung
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004591:Electrophoresis, Polyacrylamide Gel; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D005810:Multigene Family; D016805:Paramecium tetraurelia / Q000235:genetics*; D015800:Protozoan Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D002147:Calmodulin; D002352:Carrier Proteins; D018076:DNA, Complementary; D008565:Membrane Proteins; C119616:PCM1 protein, Paramecium tetraurelia; D015800:Protozoan Proteins; D002118:Calcium