Type IV collagen is the major structural component of glomerular basement membranes (GBM), forming a 'chicken-wire' meshwork together with laminins, proteoglycans and entactin/nidogen. There are six type IV collagen isoforms, alpha 1(IV)-alpha 6(IV), each of which can form a triple helix structure with 2 other chains to generate type IV collagen network. The alpha 3(IV) chain forms a triple helical protomer with alpha 4(IV) and alpha 5(IV); this triple helical structure dimerizes through NC1-NC1 domain interactions such that the alpha 3(IV), alpha 4(IV) and alpha 5(IV) chains of one protomer connect with the alpha 5(IV), alpha 4(IV) and alpha 3(IV) chains of the opposite protomer, respectively (By similarity). Associates with LAMB2 at the neuromuscular junction and in GBM. Colocalizes with COL4A3 and COL4A5 in GBM, tubular basement membrane (TBM) and synaptic basal lamina (BL). Expressed in Bruch's membrane, outer plexiform layer, inner nuclear layer, inner plexiform layer, ganglion cell layer, inner limiting membrane and around the blood vessels of the retina (at protein level) (PubMed:29777959). Highly expressed in kidney and lung (PubMed:7962065). Detected at lower levels in heart, muscle and skin (PubMed:7962065). The expression of collagen IV undergoes a developmental shift in the developing lens capsule. During the early stages of lens capsule development expression of collagens alpha 1(IV), alpha 2(IV), alpha 5(IV) and alpha 6(IV) is observed; this is consistent with the presence of fibrillar alpha 1(IV)-alpha 1(IV)-alpha 2(IV) protomers and of elastic alpha 5(IV)-alpha 5(IV)-alpha 6(IV) protomers. In the later stages of development components of the more cross-linked alpha 3(IV)-alpha 4(IV)-alpha 5(IV) protomer appear. 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. The trimeric structure of the NC1 domains is stabilized by covalent bonds between Lys and Met residues. The kidneys of transgenic mice where the 5' portions of both COL4A3 and COL4A4 and the shared intergenic promoter region were deleted exhibit morphological and ultrastructural features characteristic of the human hereditary disorder Alport syndrome, including disorganization and multilamellar structure of the GBM and delayed onset glomerulonephritis. Belongs to the type IV collagen family.