Abstract
The human lymphoid cell activation antigen CD39 is a known E-type apyrase that hydrolyzes extracellular ATP and ADP, a function important in homotypic adhesion, platelet aggregation, and removal by activated lymphocytes of the lytic effect of ATP. The recently identified putative rat homologue of CD39L1 has been shown to have E-type ecto-ATPase activity, by hydrolyzing extracellular ATP. We have characterized three novel CD39-like transcripts, CD39L2, CD39L3, and CD39L4, which share extensive amino acid homology with other nucleotide triphosphatases in vertebrates, invertebrates, and plants, suggesting that these genes also encode proteins with ecto-nucleotidase activity. Isolation and sequencing of full-length cDNA clones for each gene identified putative proteins of 485, 529, and 429 amino acids. The expression pattern of all five human members of the gene family was analyzed. CD39L2, CD39L3, and CD39L4 were mapped on the human genome, and the murine homologues identified with the putative map locations were assigned on the basis of regions of conserved gene order between human and mouse chromosomes. The map location of mcd39l4 places the gene within a region associated with audiogenic seizure susceptibility in mouse. This disorder is characterized by convulsions induced by loud high-frequency sound and has been shown to be associated with increased nucleotide triphosphatase activity.
