The principal structural elements of basement membrane are laminin (LM) and collagen IV. These form distinct networks that become noncovalently interconnected by nidogen and perlecan, both of which are able to form irregular polymers (Breitkreutz et al. 2013).
LM polymeric networks can self-assemble even in the absence of other basement membrane components (Yurchenco et al. 1992) suggesting a key developmental role. Polymerization in vivo occurs at the cell surface, to which LMs are anchored through direct or indirect interactions with cellular receptors, dystroglycan or integrins, and possibly other receptors (Hohenester & Yurchenco 2013).
Receptor-engaged LM exceeds the critical concentration for self-assembly (Colognato & Yurchenco 2000).
The three short arms of the cross-shaped LM molecule form the nodes in the polymeric network, with a strict requirement for one each of alpha, beta and gamma arms (Hohenester & Yurchenco 2013). A surface loop, strictly conserved in the LN domains of all alpha chains, is required for stable ternary association with the beta and gamma short arms (Hussain et al. 2011).