American oyster, Crassostrea virginica, expresses a potent antibacterial histone H2B protein.

An antibacterial protein was purified from acidified gill extract of a bivalve mollusk, the American oyster (Crassostrea virginica). Protein isolation was best accomplished by briefly boiling the tissues in a weak acetic acid solution. Adding protease inhibitors while boiling did not have a major effect on activity recovery. In contrast, use of only protease inhibitors (without boiling) resulted in virtually no recovery of this activity. The amino acid sequence of this antibacterial protein was identified as a histone H2B and was designated cvH2B. cvH2B had potent activity against gram-negative bacteria, including the human pathogens Vibrio parahaemolyticus and Vibrio vulnificus, which commonly reside in oyster tissues. We estimated that the concentration of this protein was well within the concentration that was inhibitory to these bacterial pathogens in vitro. This is the first report of the antimicrobial function of histone H2B from any mollusk.