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J. Biol. Chem., Vol. 277, Issue 43, 40729-40734, October 25, 2002

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An ATP-binding Cassette Transporter Is a Major Glycoprotein of Sea Urchin Sperm Membranes^*

Kathryn J. Mengerink and Victor D. Vacquier

From the Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0202

Sperm are terminally differentiated cells that undergo several membrane-altering events before fusion with eggs. One event, the sea urchin sperm acrosome reaction (AR), is blocked by the lectin wheat germ agglutinin (WGA). In an effort to identify proteins involved in the AR induction, the peptide sequence was obtained from a 220-kDa WGA-binding protein. Degenerate PCR and library screening resulted in the full-length deduced amino acid sequence of an ATP-binding cassette transporter, suABCA. The protein of 1,764 residues has two transmembrane regions, two nucleotide-binding domains, and is most closely related to the human ABC subfamily A member 3 transporter (ABCA3). Sequence analysis suggests a large extracellular loop between transmembrane spanning segments 7 and 8, with five N-linked glycosylation sites. An antibody made to the loop region binds to non-permeabilized cells, supporting that this region is extracellular. suABCA is found in sperm membrane vesicles, it can be solubilized with nonionic detergents, and it shifts from 220 to 200 kDa upon protein:N-glycanase F digestion. suABCA localizes to the entire surface of sperm in a punctate pattern, but is not detected in lipid rafts. Based on its relationship to subfamily A, suABCA is most likely involved in phospholipid or cholesterol transport. This is the first investigation of an ABC transporter in animal sperm.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) AF529424.

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