The IG3 repeat in domain IV of perlecan is the principal site of interaction with nidogen-1, binding to the G2 domain. Nidogen-1 in turn binds to the laminin gamma1-subunit (Mayer et al. 1998), providing a bridge between the two proteins (Hopf et al. 1999, 2001, Kvansakul et al. 2001). Perlecan also binds to nidogen-2 (Battaglia et al. 1992, Reinhardt et al. 1993, Kohfeldt et al. 1998).