This superfamily consists of several eukaryotic apyrase (or adenosine diphosphatase) proteins (EC:3.6.1.5) and related nucleoside diphosphatases (EC:3.6.1.6). The salivary apyrases of blood-feeding arthropods are nucleotide hydrolysing enzymes implicated in the inhibition of host platelet aggregation through the hydrolysis of extracellular adenosine diphosphate PMID:9804829,PMID:12234496. Soluble calcium-activated nucleotidase 1 (CANT1) is the human homologue PMID:15248776.

The apo structure reveals an unusual five-bladed beta propeller. The five twisted beta-sheets (1-5), each formed from four antiparallel beta strands (a, b, c, and d), are radially arranged around a central tunnel. The interface between neighbouring blades is predominantly hydrophobic, with residues on the adjacent faces of the beta sheets in van der Waals contact. The central tunnel is slightly conical in shape and is lined with amide and carbonyl oxygen groups from the edges of the five inner strands, with only a few side chains projecting into the cavity. Structural and biochemical analysis suggests that the striking difference in substrate preference between human and insect apyrases (GDP versus ADP) results from divergence at one or more of the nonconserved active-site residues.

PFAM:PF06079, INTERPRO:IPR009283,DOI:10.1016/S0092-8674(04)00172-2