title: A novel G protein alpha subunit containing atypical guanine nucleotide-binding domains is differentially expressed in a molluscan nervous system.
abstract: We described the characterization of a novel G protein alpha subunit, G alpha a. cDNA encoding this subunit was cloned from the central nervous system of the mollusc Lymnaea stagnalis. The deduced protein contains all characteristic guanine nucleotide-binding domains of G alpha subunits but shares only a limited degree of overall sequence identity with known subtypes (approximately 30%). Moreover, two of the nucleotide-binding domains exhibit salient deviations from corresponding sequences in other G protein alpha subunits. The A domain, determining kinetic features of the GTPase cycle, contains a markedly unique amino acid sequence (ILIIGGPGAGK). In addition, the C domain is also clearly distinct (DVAGQRSL). The presence of a leucine in this motif, instead of glutamic acid, has important implications for hypotheses concerning the GTPase mechanism. In contrast to other G alpha subtypes, G alpha a has no appropriate N-terminal residues that could be acylated. It does contain the strictly conserved arginine residue that serves as a cholera toxin substrate in G alpha s and G alpha t but lacks a site for ADP-ribosylation by pertussis toxin. In situ hybridization experiments indicate that G alpha a-encoding mRNA is expressed in a limited subpopulation of neurons within the Lymnaea brain. These data suggest that G alpha a defines a separate class of G proteins with cell type-specific functions.
authors.affiliation: Graduate School of Neurosciences Amsterdam, Research Institute Neurosciences Vrije Universiteit, Faculty of Chemistry, Department of Biochemistry and Molecular Biology, The Netherlands.
authors.forename: J C
authors.initials: JC
authors.lastname: Knol
authors.forename: A R
authors.initials: AR
authors.lastname: van der Slik
authors.forename: E R
authors.initials: ER
authors.lastname: van Kesteren
authors.forename: R J
authors.initials: RJ
authors.lastname: Planta
authors.forename: H
authors.initials: H
authors.lastname: van Herikhuizen
authors.forename: E
authors.initials: E
authors.lastname: Vreugdenhil
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D018076:DNA, Complementary / Q000302:isolation & purification; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics; D006150:Guanine Nucleotides / Q000378:metabolism*; D008195:Lymnaea / Q000737:chemistry*; D008969:Molecular Sequence Data; D011499:Protein Processing, Post-Translational
chemical_list: D018076:DNA, Complementary; D006150:Guanine Nucleotides; D019204:GTP-Binding Proteins