Characterization of a serine/threonine protein phosphatase regulatory subunit in the Indian pearl mussel

Reversible phosphorylation is a key mechanism for regulating the biological activities of functional proteins. We have partially characterized a serine/ threonine phosphatase 6 regulatory protein from the mantle tissues of Indian freshwater pearl mussels Lamellidens marginalis and Parreysia corrugata. The characterized sequences showed more than 75% sequence identity at both the DNA and protein levels of the species. Importantly, the characterized sequences did not show similarity to any other genes in the homology search. A predicted 23 amino acid polypeptide stretch from both the species was 100% identical in all mollusc sequences available till date (across isoforms) and more than 95% similar to a wide range of species. The predicted protein folding patterns showed alpha helices separated by intervening loop regions in both the in silico translated polypeptides, similar to reported regulatory subunits of serine/ threonine protein phosphatases. Considering the extent of structural similarity of this polypeptide stretch among the molluscs and the fact that the sequences were isolated from the mantle tissues, it may be speculated that the genes partially characterized here could be primarily involved in shell formation and bio-mineralization process.