Abstract

A cDNA encoding for the cell-surface glycoprotein CD4 from an odontocete cetacean, the Atlantic bottlenosed dolphin (Tursiops truncatus), was cloned and sequenced. An open reading frame of 1,368 bp translates into a 455 amino acid polypeptide containing four extracellular immunoglobulin-like domains, a transmembrane region, and a cytoplasmic tail. Compared to (Delphinapterus leucas) sharing 98% homology at the nucleotide level and 97% at the amino acid level. Dolphin CD4 also shares the unique property of a missing cysteine pair in the V2 domain that is common in whale, dog, and cat. The seven potential N-linked glycosylation sites in dolphin CD4 are identical to those in whale yet only one site is shared in common with human and mouse. Furthermore, the cytoplasmic tail in dolphin CD4 shares unique amino acid substitutions with whale at positions that are highly conserved amongst terrestrial mammals. The high similarity between dolphin and whale CD4 correlates with their close evolutionary relationship and suggests unique structural and perhaps functional properties of this molecule in marine mammals.

Acknowledgements

This work was supported by a grant from the Office of Naval Research (N00014-00-1-0041). The authors would like to thank the veterinary and animal training staff of the U.S. Navy Marine Mammal Program.