title: A sodium bicarbonate transporter from sea urchin spermatozoa.
abstract: Bicarbonate (HCO3-) transporters play crucial roles in cell-signaling pathways and are essential for cell viability. Here we describe the first cloning and localization of a HCO3- transporter from sperm of the sea urchin, Strongylocentrotus purpuratus. The deduced protein is 1214 amino acids and has a calculated molecular mass of 135 kDa. The annotated protein coding region of the transporter gene consists of 24 exons. The most similar human protein is the Na+/HCO3- cotransporter-2 (NBC2), which has 53% identity and 68% similarity to the sea urchin protein. The sea urchin protein shares the major structural features of HCO3- transporters, including 13 transmembrane segments, a DIDS (4,4-diiodothiocyanatostilbene-2, 2-disulfonic acid) binding motif and N-linked glycosylation sites. It has longer N- and C-terminal cytoplasmic domains compared to human HCO3- transporters. The sea urchin protein possesses a relatively long 3rd extracellular loop with four conserved cysteine residues. This is characteristic for Na+/HCO3- cotransporters, but not for anion exchangers, suggesting that the sea urchin protein is a Na+/HCO3- cotransporter. It is therefore designated as Sp-NBC. A neighbor-joining tree shows that Sp-NBC branches closer to the electroneutral type of HCO3- transporters. Western immunoblots and immunoflourescence show that Sp-NBC is concentrated in the flagellar plasma membrane, suggesting a role in motility regulation.
authors.affiliation: Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202, USA. hgunarat@ucsd.edu
authors.forename: Herath Jayantha
authors.initials: HJ
authors.lastname: Gunaratne
authors.forename: Mamoru
authors.initials: M
authors.lastname: Nomura
authors.forename: Gary W
authors.initials: GW
authors.lastname: Moy
authors.forename: Victor D
authors.initials: VD
authors.lastname: Vacquier
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D003001:Cloning, Molecular; D005455:Fluorescent Antibody Technique; D008969:Molecular Sequence Data; D010802:Phylogeny; D012617:Sea Urchins; D017386:Sequence Homology, Amino Acid; D027982:Sodium-Bicarbonate Symporters / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D027982:Sodium-Bicarbonate Symporters