Collagen Type IV (COL4)

Type-IV collagen is a type of collagen found primarily in the basal lamina. The C-terminus domain is not removed in post-translational processing, and the fibers link head-to-head, rather than in parallel. Also, type-IV lacks the regular glycine in every third residue necessary for the tight, collagen helix. This makes the overall arrangement more sloppy with kinks. These two features cause the collagen to form in a sheet, the form of the basal lamina.

All of the type IV collagen in mammals is derived from six genetically distinct a-chain polypeptides (a1–a6). The type IV collagen a-chains have similar domain structures and share between 50–70% homology at the amino-acid level. The a-chains can be separated into three domains: an amino-terminal 7S domain, a middle triple-helical domain, and a carboxy-terminal globular non-collagenous (NC)-1 domain (see figure).