Purification and partial characterization of a lectin-like protein from the sea algae Laminaria diabolica that induces fertilization envelope formation in sea urchin eggs

When unfertilized eggs of the sea urchin Hemicentrotus pulcherrimus were tr eated with the extracts from the sea algae Laminaria diabolica, fertilizati on envelope formation (FEF) was observed in 1.5 to 2 min without subsequent cleavage. The molecular mass of the FEF-inducing protein purified from the Laminaria extracts was estimated by gel-filtration to be 120 kDa, and it i nduced a 100% FEF at a concentration of 525 ng/ml (4.4 nM). The FEF activit y of the purified protein was completely inhibited by GlcNAc, less effectiv ely by GlcN, and not at all by various other sugars and amino-sugars, sugge sting its nature as a lectin. Normal FEF and cleavage were observed when eg gs were inseminated in the presence of GlcNAc. Immunohistochemical observat ions using antibodies against purified protein revealed its specific locali zation in the cells lining the wall of mucilaginous lacunae and in secretor y products in the lumen. The purified protein did not activate the pretreat ed with verapamil or diltiazem, while ionomycin, a Ca2+-ionophore, did indu ce activation of the similarly pretreated eggs. These results indicate that the Laminaria lectin triggers a very initial step in the cascade of the eg g cortical reactions leading to FEF, independently of those induced by sper m.