Zigler, K.S.: The sea urchin sperm protein bindin is conserved throughout the echinoids

The sea urchin sperm protein bindin is the principal component of the acrosomal vesicle and is involved in sperm-egg recognition and sperm-egg fusion. Bindin is not homologous to any known non-echinoid protein. Bindin is only known from several genera of regular echinoids. We have cloned mature bindin sequences from a range of other echinoids including a sand dollar (Encope stokesi), a heart urchin (Moira atropos), a diadematoid (Diadema antillarum), and a pencil urchin (Eucidaris tribuloides). The core region of bindin, which is involved in sperm-egg fusion, is extremely conserved. The regions flanking the core, which are involved in species-specific sperm-egg recognition, are remarkably divergent. These results indicate that the bindin molecule has been conserved in the echinoids for over 250 million years.