Molecular cloning of a new member of the putative G protein-coupled receptor gene from barnacle Balanus amphitrite

An intronless gene encoding a putative G protein-coupled receptor was isolated from the genomic library of barnacle Balanus amphitrite Darwin, with probes obtained from degenerate polymerase chain reaction (PCR) primers used to amplify putative transmembrane regions. The cloned genome DNA specifies an open reading frame of 1431 bp encoding 476 amino acids with seven hydrophobic transmembrane (TM)-spanning regions. The predicted protein contains potential asparagine-linked glycosylation and serine/threonine phosphorylation sites in the N-terminal and intracellular loops, respectively. Moreover, the protein has a consensus G protein-binding motif (Ala-Ile-Ser-Leu-Asp-Arg-Tyr-Leu-Ala) in TM domain III. This receptor is most closely related to human alpha(2)-adrenergic receptor with 36.9% identity in 409 amino acids overlap. It is also homologous to human serotonin(1A) (5HT), snail pond 5HT and mouse D-2-dopamine receptors with 33-36% identities. Within TM regions among these biogenic amine receptors, the cloned receptor shows considerable amino acid homology with more than 40% overall identities.