CEL-III is a hemolytic lectin purified from the marine invertebrate Cucumaria echinata. Previous research has indictated that CEL-III is composed of several isoforms. Here we identified five CEL-III isolectin genes, designated CEL-III-L1, CEL-III-L2, CEL-III-S1, CEL-III-S2, and CEL-III-LS1, by cDNA cloning. The deduced amino acid sequences suggested they shared 94.0–99.8% identical residues. Among the amino acid residues involved in carbohydrate binding, the His residue, which contributes to stacking with sugar, in subdomain 1α was replaced by Tyr in CEL-III-L2. The recombinant proteins were expressed in Escherichia coli or insect cells. rCEL-III-L2 showed higher hemolytic activity than those of the other isolectins. Furthermore, an apparent oligomer band of rCEL-III-L2 was detected on erythrocyte membranes, although the other isolectins showed smear bands. These results suggest that Tyr36 of CEL-III-L2 is important for the expression of hemolytic activity and oligomerization.

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