[The homology of the primary structure of the third cytoplasmic domains in rhodopsin-type receptors and of the cytoplasmic tail in the beta-subunit of the insulin receptor].

In the last years evidence has been provided that along with the main mechanism of insulin signal transduction, that involves the ligand-induced tyrosine kinase cascade mediating the majority of biological effects of insulin, there is another signalling mechanism involving the heterotrimeric G-proteins. To detect the regions of amino acid sequences (AAS), responsible for interaction between the insulin receptor (IR) and G-proteins, a comparative analysis was carried out of the primary structure of third cytoplasmic domains (CD3) of rhodopsin-related receptors (RRR) determining RRR coupling to G-proteins, and of the primary structure of the cytoplasmic tail of IR beta-subunit. It is shown that AAS of juxtamembrane, ATP-binding and C-terminal domains of IR include long regions, homologous to the regions of RRR CD3, which are functionally important for coupling with G-proteins. AAS alignment of homologous RRR CD3 and beta-subunit of IR regions was made. It is found that the clusters of basic amino acids (e.g. forming BBXXB-motifs) and serine residues, located in RRR, coincide with similar amino acids present in IR primary structure. It is known that: 1) the BBXXB-motifs participate in the interaction with G-protein molecules, and 2) serine residues, the targets for phosphorylation by protein kinases, are included in regulation of hormonal signalling for both the receptor types. So, in the primary structure of IR beta-subunit, the regions were identified, which can be molecular determinants included in specific interaction with G-proteins of different types.