Abstract

The main hemolymph protein of the majority of bivalves corresponds to a high molecular weight protein whose biological function has not been established yet. We have isolated this protein (PMHC) from Choromytilus chorus hemolymph and demonstrated that it corresponds to an acidic his dine-rich glycoprotein (pI=5.9) displaying a homomultimeric quaternary structure with a particle of 40nm under native conditions, and with a monomer size of 75 kDa. The amino terminal sequence of PMHC, obtained by Edman degradation, matches perfectly with the sequence of the main hemolymph protein from Perna canaliculus (pernin). The analysis of the tryptic map using the Sequest tool allowed confirming that PMHC corresponds to a pernin-like protein. Also, PMHC de novo sequencing was performed using mass spectrometry, obtaining the sequence of several peptides that align with pernin, cavortin and dominin, all corresponding to major proteins from bivalve hemolymph. In silico analyses show that all four proteins share the sequence ACCV and also a common superoxide dismutase (SOD) domain which is triplicated in pernin. It is interesting to highlight that PMHC displays an microbial activity against E. coli in vitro, suggesting that this protein could be a component of the innate immune system of C. chorus. In addition, this protein constitutes a very good antigen since a highter an serum was obtained in rabbits immunized only with the purified protein. Based on its abundance, easy purification, size and antigenicity it has biotechnological potential as a carrier protein.