A Disintegrin And Metalloprotease 21 (ADAM21)

Members of the ADAM protein family are type I integral membrane proteins. Northern blot analysis detected ADAM20 and ADAM21 expression as approximately 2.8-kb mRNAS, with ADAM21 being slightly shorter, only in testis. Like ADAM20, the predicted 542-amino acid ADAM21 protein contains putative cell-fusion peptides required for sperm-egg fusion. Overall, the 2 proteins are 50% identical and share sequence similarity with ADAM9 and mammalian fertilin-alpha and -beta. The exclusive expression of ADAM20 and ADAM21 in human testis and their sequence similarity with the fertilins suggested that they too are expressed on sperm cells and are involved in sperm maturation and/or fertilization. ADAM20 and/or ADAM21 is the functional equivalent of sperm fertilin-alpha, since that gene is nonfunctional in human.