G-protein coupled receptors

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GPCRs form one of the largest families of proteins that have a key role in human physiology. They allow detection and transduction of a large variety of extracellular signals such as ions, odorants, amino acids, peptides, neurotransmitters, hormones, nucleotides and fatty acids. Although they are activated by a diverse set of ligands, they share a common structural motif consisting of seven transmembrane regions. GPCRs are subdivided into six major families, but aside from their conserved secondary domain structure there is no significant sequence similarity across families. In Dictyostelium discoideum only four members of one family, the cAMP receptor/cAMP receptor-like (CRL) family, have been previously identified. Surprisingly, the genome sequence revealed numerous and diverse additional GPCRs belonging to family 2, 3 and 5 and homologs of two orphan receptors. Representatives of these families are also present in Dictyostelium fasciculatum and Polysphondylium pallidum, which are members of the early diverging Dictyostelidae groups 1 and 2, respectively. Here we want to investigate the function of RpkA and GPR89. RpkA is a member of the CRL family and homologs have been found in the plant pathogen Phythophtora and in lower metazoa. GPR89, an orphan receptor, is highly conserved. The plant homolog has been described as abscisic acid repector whereas the mammalian homolog was identified as chloride channel in the Golgi.