The netrin family of proteins. (a) Netrins are members of the laminin superfamily. A phylogenetic tree based on human protein sequences illustrates the relationship between netrin and laminin family members. (b) Laminin 1 is a heterotrimer composed of α (blue), β (green), and γ (turquoise) chains. The amino-terminal VI and V domains of netrins 1 to 3 (red) are homologous with the γ chain of laminin 1. These domains in netrins 4, G1 and G2 are more similar to the β chain of laminin 1. (c) Domain organization of the netrin family members. Netrins 1 to 4 are secreted proteins and contain a carboxy-terminal C-domain (C), whereas netrins G1 and G2 are linked to the plasma membrane by a GPI linker (magenta).