Purification of a novel antibacterial and haemagglutinating protein from the purple gland of the sea hare, Aplysia dactylomela Rang, 1828

Physicochemical characterisation and antibacterial and haemagglutinating pr operties of a new protein isolated from purple fluid of the Aplysia dactylo mela are reported. The purification procedure consisted basically of ammoni um sulphate fractionation, ion exchange, exclusion molecular and hydrophobi c interaction chromatography. The highly purified protein, designated dacty lomelin-P, is a single chain protein of 60,000 Da by SDS-polyacrylamide gel electrophoresis and 56,200 Da by gel filtration on calibrated Superose col umn at pH 7.5 and contains less than 0.05% of its weight in neutral carbohy drates. Dactylomelin-P has two biological activities, antibacterial and hae magglutinating. The antibacterial action is bacteriostatic but not bacteric idal. The haemagglutinating activity is preferentially against rabbit eryth rocytes. The glycoprotein fetuin was able to abolish the haemagglutinating activity but not the antibacterial one even when used at concentrations 10 fold higher. This is the first time that a chimeroprotein is described in t he purple fluid of sea hares, which may be involved in the chemical defence mechanism of these organisms. (C) 2000 Elsevier Science Ltd. All rights re served.