CHARACTERIZATION OF A PUTATIVE MOLLUSCAN INSULIN-RELATED PEPTIDE RECEPTOR

In the pond snail Lymnaea stagnalis (Ls), growth and associated proces ses are likely to be controlled by a family of molluscan insulin-relat ed peptides (MIP). Here we report on the cloning of a cDNA encoding a putative receptor for these MIP. This cDNA was isolated from Ls via PC R with degenerate oligodeoxynucleotides corresponding to conserved par ts of the tyrosine kinase domain of the human insulin receptor and its Drosophila homologue. Many of the typical insulin-receptor features, including a cysteine-rich domain, a single transmembrane domain and a tyrosine-kinase domain are conserved in the predicted, 1607-amino acid (aa) protein. Comparison of the aa sequence of the molluscan receptor to other insulin-receptor sequences revealed strong variations in the percentage of sequence identity for the different domains, ranging fr om 70% sequence identity in the tyrosine-kinase domain to virtually no sequence identity in the C-terminal sequence. Striking differences ar e the absence of a clear tetrabasic cleavage site, and the extremely l ong C-terminus of 308 aa that contains seven Tyr residues. Southern bl ot analyses at varying stringencies, extensive screening of cDNA- and genomic libraries, and PCR experiments indicate the presence of a sing le putative MIP receptor. This suggests that the four different MIP ma y exert their functional role in Ls by binding to the same receptor.