Type IV Collagen of Basal Lamina

Type IV collagens are non-fibrillar or network-forming collagens which are primarily found in the basal lamina.

A typical type IV collagen is a 400 nm long, triple-helical structure interrupted by several non-helical regions which add flexibility to the molecule.

At the N-terminal, it has a small globular domain, while a large globular domain is present at the C-terminal.

Through these terminal globular domains, the collagen fibres can associate with each other by head-to-head interactions forming a dimer; and tail-to-tail interactions forming a tetramer. The fibres also associate by lateral interactions between the triple-helical regions. 

Such complex associations can form a two dimensional, irregular network, which provides tensile strength to the basal lamina.

This network further links with the laminin lattice and other glycoproteins such as perlecan and entactin,  to build a complete basal lamina.