Disintegrin and metalloproteinase domain-containing protein 20 is an enzyme encoded by the ADAM20gene in humans. It is a membrane disintegrin-metalloprotease that belongs to the ADAM family. It is exclusively expressed in the Testes and is similar to sperm cell-specific fertilins -alpha and -beta.
Its cDNA is tightly linked to marker SHGC-36001 on chromosome 14q24.1. ADAM20 is related to fertilin α (ADAM1A/B pseudogene), fertilin β (ADAM2), and fertilin γ (ADAM9). In humans, fertilin α has recently been deactivated so that ADAM20 may be the functional equivalent of fertilin α in humans.[5]
Computed structure of the ADAM 20 protein.[6] The signal and propeptide sites have been removed as they would be cleaved in the active form. Extracellular domains are highlighted in red, helical domains are in yellow, and cytoplasmic domains are in blue.
In common with other ADAM family members, ADAM20 contains a N-terminal reprolysin family propeptide (residues 57–159), reprolysin (M12B) family zinc metalloprotease domain (207–395), disintegrin domain (416–488), and a C-terminal ADAM cysteine-rich domain (493–605).[7]
The propeptide acts as a signal peptide and an activator domain. This prodomain has a cysteine that interacts with a zinc in the catalytic domain, thereby preventing the catalytic activity of the protein. When the pro-protein domain is cleaved, this cysteine zinc bond is broken, and the protein is activated.[8] A notable variant showed an amino acid difference in the pro protein domain that prevented the cleavage of this domain, which prevented the fusion of the sperm cell to an egg.[9]
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Hooft van Huijsduijnen R (January 1998). "ADAM 20 and 21; two novel human testis-specific membrane metalloproteases with similarity to fertilin-alpha". Gene. 206 (2): 273–82. doi:10.1016/s0378-1119(97)00597-0. PMID9469942.
