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ADAM2
ADAM2 Full Name
ADAM metallopeptidase domain 2
ADAM2 Introduction
ADAM2, also known as fertilin β, is a member of the ADAM (a disintegrin and metalloproteinase) family of transmembrane proteins. The gene encoding ADAM2 is located on human chromosome 8p11.22 and produces a protein of approximately 719 amino acids. ADAM2 is best known for its essential role in mammalian fertilization. It was originally identified as a subunit of fertilin, a heterodimeric sperm surface protein composed of ADAM1 (fertilin α) and ADAM2 (fertilin β). Unlike many other ADAM family members, ADAM2 lacks a functional catalytic metalloprotease domain because the critical zinc-binding motif is degenerate. Therefore, ADAM2 functions primarily as an adhesion molecule rather than a protease. Its expression is highly restricted to the testis and sperm, where it is involved in sperm-egg membrane interactions during fertilization.
Figure 1. Proteolytic processing of fertilin during sperm maturation in the testis and epididymis.( Blobel, Carl P, 2000)
Structural Domains of ADAM2
ADAM2 shares the typical multidomain architecture of ADAM proteins but with a non-functional metalloprotease domain. It contains a signal peptide, a prodomain, a metalloprotease-like domain that lacks the catalytic HEXXHXXGXXH zinc-binding motif (replaced by an inactive sequence), a disintegrin domain, a cysteine-rich region, an EGF-like repeat, a transmembrane helix, and a cytoplasmic tail. The disintegrin domain of ADAM2 is particularly important because it contains a tripeptide sequence (often ECD or related motifs) that binds to integrins on the egg plasma membrane. The prodomain is proteolytically removed during sperm maturation in the epididymis, allowing the mature protein to be exposed on the sperm surface. The cysteine-rich region contributes to protein-protein interactions, including the heterodimerization with ADAM1. The transmembrane domain anchors ADAM2 in the sperm plasma membrane, while the short cytoplasmic tail may interact with intracellular signaling molecules.
Role of ADAM2 in Fertilization
ADAM2 is a critical component of the sperm-egg adhesion machinery. On the surface of mature sperm, ADAM2 forms a heterodimeric complex with ADAM1 (fertilin α). This fertilin complex is located on the equatorial segment and posterior head region of the sperm, where it mediates binding to the egg's plasma membrane. The disintegrin domain of ADAM2 recognizes and binds to integrins (specifically α6β1 or α9β1) on the egg surface. This interaction is species-specific and essential for successful fertilization. Studies in mice have demonstrated that Adam2 knockout males are infertile; their sperm are unable to bind to the zona pellucida or fuse with the egg membrane. The infertility phenotype is characterized by impaired sperm-egg adhesion and defective migration of sperm through the female reproductive tract. These findings confirm that ADAM2 is indispensable for mammalian fertilization.
Alternate Names for ADAM2
ADAM2; ADAM metallopeptidase domain 2; fertilin beta; FTNB; disintegrin and metalloproteinase domain-containing protein 2; cancer/testis antigen 15; CT15; PH 30b; PH30; PH-30; ADAM 2; PH30-beta; fertilin beta; fertilin subunit beta; FTNB; CRYN1; CRYN2; PH-30b;
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