title: Phosphorylation of a Ras-related GTP-binding protein, Rap-1b, by a neuronal Ca2+/calmodulin-dependent protein kinase, CaM kinase Gr.
abstract: A neuron-specific Ca2+/calmodulin-dependent protein kinase, CaM kinase Gr, phosphorylates selectively a Ras-related GTP-binding protein (Rap-1b) that is enriched in brain tissue. The phosphorylation reaction achieves a stoichiometry of about 1 and involves a serine residue near the carboxyl terminus of the substrate. Both CaM kinase Gr and cAMP-dependent protein kinase, but not CaM kinase II, phosphorylate identical or contiguous serine residues in Rap-1b. The rate of phosphorylation of Rap-1b by CaM kinase Gr is enhanced following autophosphorylation of the protein kinase. Other low molecular weight GTP-binding proteins belonging to the Ras superfamily, including Rab-3A, Rap-2b, and c-Ha-ras p21, are not phosphorylated by CaM kinase Gr. The phosphorylation of Rap-1b itself can be reversed by an endogenous brain phosphoprotein phosphatase. These observations provide a potential connection between a neuronal Ca2(+)-signaling pathway and a specific low molecular weight GTP-binding protein that may regulate neuronal transmembrane signaling, vesicle transport, or neurotransmitter release.
authors.affiliation: Wellcome Research Laboratories, Research Triangle Park, NC 27709.
authors.forename: N
authors.initials: N
authors.lastname: Sahyoun
authors.forename: O B
authors.initials: OB
authors.lastname: McDonald
authors.forename: F
authors.initials: F
authors.lastname: Farrell
authors.forename: E G
authors.initials: EG
authors.lastname: Lapetina
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000201:enzymology*; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002531:Cerebellum / Q000201:enzymology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008969:Molecular Sequence Data; D009474:Neurons / Q000201:enzymology*; D010455:Peptides / Q000138:chemical synthesis; D010766:Phosphorylation; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D020668:rap GTP-Binding Proteins
chemical_list: D010455:Peptides; D011518:Proto-Oncogene Proteins; D011494:Protein Kinases; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C517686:Camk4 protein, rat; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins