Crystal structure and mutational analysis of a perlecan-binding fragment of nidogen-1

Nidogen, an invariant component of basement membranes, is a multifunctional protein that interacts with most other major basement membrane proteins. Here, we report the crystal structure of the mouse nidogen-l GZ fragment, which contains binding sites for collagen IV and perlecan. The structure is composed of an EGF-like domain and an Ii-stranded beta -barrel with a central helix. The beta -barrel domain has unexpected similarity to green fluorescent protein. A large surface patch on the beta -barrel is strikingly conserved in all metazoan nitrogens. Site-directed mutagenesis demonstrates that the conserved residues are involved in perlecan binding.