RESUMEN
The squid (Loligo forbesi) visual system presents as accessible a system for study of G-protein mediated signal transduction as the vertebrate rod outer segment with the added advantage that the major G-protein is a member of the Gq-class. Here the cDNA clone encoding the gamma-subunit of this G-protein is reported, thereby completing the molecular cloning of the heterotrimeric G-protein. The deduced protein structure of G-gamma has relatively little sequence identity with known mammalian counterparts particularly in comparison with the relatively high degree found for both the alpha- and beta-subunits of this protein. In particular, the N-terminus of the squid visual G-gamma contains a repetitive, highly charged region, rich in lysine and glutamate, that has no parallel in other G-proteins. The amino acid sequence of a number of peptides derived by chemical cleavage of G-gamma accounted for much of the protein sequence predicted from the cDNA, including the unusual N-terminal region.
Asunto(s)
Proteínas de Unión al GTP/genética , Células Fotorreceptoras/química , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Northern Blotting , ADN , Decapodiformes , Datos de Secuencia Molecular , Homología de Secuencia de AminoácidoRESUMEN
The principal GTP-binding protein (G-protein) from squid (Loligo forbesi) photoreceptor membranes has been identified by amino acid sequencing. The heterotrimeric protein was purified by detergent solubilization and ion-exchange chromatography. The amino acid sequence of the G-protein alpha-subunit (G-alpha) indicates that this subunit is closely related to the recently characterized Gq subgroup, whereas the G-gamma subunit varies widely in sequence from other homologues.
Asunto(s)
Proteínas de Unión al GTP/aislamiento & purificación , Células Fotorreceptoras/química , Secuencia de Aminoácidos , Animales , Cromatografía por Intercambio Iónico , Bromuro de Cianógeno , Decapodiformes , Detergentes , Electroforesis en Gel de Poliacrilamida , Proteínas de Unión al GTP/química , Yodobenzoatos/química , Datos de Secuencia Molecular , Homología de Secuencia de Ácido Nucleico , Urea/químicaRESUMEN
The beta-subunit (G-beta) of the squid (Loligo forbesi) visual GTP-binding protein (G-protein), thought to be associated with a phosphatidylinositol-specific phospholipase C, has been identified and the sequence of the protein determined from its cDNA. The predicted polypeptide has a very marked sequence similarity with its mammalian counterparts (80-90% identity). Squid G-beta also has somewhat lower similarity to the yeast protein STE4 (approx. 40% identity). The role of G-beta in signal transduction is discussed in the light of its pronounced structural conservation.
Asunto(s)
Proteínas de Unión al GTP/genética , Fosfatidilinositoles/metabolismo , Células Fotorreceptoras/metabolismo , Fosfolipasas de Tipo C/metabolismo , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Bovinos , ADN/genética , Decapodiformes , Drosophila/genética , Electroforesis en Gel de Poliacrilamida , Humanos , Datos de Secuencia Molecular , Saccharomyces cerevisiae/genética , Homología de Secuencia de Ácido NucleicoRESUMEN
The sequence of squid (Loligo forbesi) rhodopsin was determined by protein and cDNA sequencing. The protein has close similarity to octopus rhodopsin, having an N-terminal region (residues 1-340) which resembles other guanine-nucleotide-binding protein (G-protein)-linked receptors and a repetitive proline-rich C-terminus (residues 340-452). Comparison of the sequence of squid rhodopsin with those of other members of the G-protein-linked receptor superfamily reveals features which we predict to have both structural and functional importance.