Nidogen, an invariant component of basement membranes, is a multifunctional protein that interacts with most other major basement membrane proteins. The G2 fragment or (G2F domain) contains binding sites for collagen IV and perlecan. The structure is composed of an 11-stranded beta-barrel with a central helix. This domain is structurally related to that of green fluorescent protein pfam01353. A large surface patch on the beta-barrel is conserved in all metazoan nidogens.