Collagen type IV is specific for basement membranes. Trimers of two alpha 1(IV) and one alpha 2(IV) chain. Type IV collagen forms a mesh-like network linked through intermolecular interactions between 7S domains and between NC1 domains. Alpha chains of type IV collagen have a non-collagenous domain (NC1) at their C-terminus, frequent interruptions of the G-X-Y repeats in the long central triple-helical domain (which may cause flexibility in the triple helix), and a short N-terminal triple-helical 7S domain. Prolines at the third position of the tripeptide repeating unit (G-X-Y) are hydroxylated in some or all of the chains. Type IV collagens contain numerous cysteine residues which are involved in inter- and intramolecular disulfide bonding. 12 of these, located in the NC1 domain, are conserved in all known type IV collagens. Belongs to the type IV collagen family.