EXPRESSION CLONING OF AN EQUINE T-LYMPHOCYTE GLYCOPROTEIN CD2 CDNA STRUCTURE-BASED ANALYSIS OF CONSERVED SEQUENCE ELEMENTS

An equine CD2 cDNA has been isolated by monoclonal antibody screening of a T-lymphocyte cDNA library. The cDNA contained an open reading fra me of 1041 bp encoding a translated product of 347 amino acids. Northe rn blotting analysis revealed a single mRNA species expressed in splee n, thymus and activated peripheral lymphocytes. The predicted amino ac id sequence has 50-65% identity with the human, rat and mouse CD2 sequ ences with greatest similarity shared with the human homologue. Evolut ionarily conserved structural and functional domains in CD2 were ident ified by comparing the sequences of the equine, human, mouse and rat C D2 homologues in the context of the recently derived crystal structure of rat soluble CD2 [Jones, E. Y., Davis, S. J., Williams, A, E, Harlo s, K. and Stuart, D. I. (1992) Nature 360, 232-239]. The key conserved features of the extracellular region included core residues necessary to preserve the structural integrity of the molecule, residues in the linker region likely to maintain the unique domain organization of CD 2, an array of highly charged residues in the putative ligand-binding face of the molecule and glycosylation-signal distributions that rende r the putative ligand-binding GFCC'C'' face of domain 1 relatively unh indered by glycosylation.