BINDING OF MOUSE AND HUMAN FIBULIN-2 TO EXTRACELLULAR-MATRIX LIGANDS

Recombinant mouse and human fibulin-2 were obtained as disulfide-bonde d trimers from transfected kidney cell clones and used in solid phase, biosensor and radioligand binding assays. Strong binding occurred wit h fibronectin and required calcium. A distinct interaction was also ob served with nidogen but this was only partially blocked by EDTA. Disti nctly weaker affinities were detected for collagen IV, perlecan and th e N-terminal globule of collagen VI alpha 3 chain, while no or only li ttle binding activity could be detected for several other collagen typ es, laminin-1, BM-40, fibulin-1 and vitronectin. This weaker binding r eactions were also dependent on calcium. Surface plasmon resonance ass ays demonstrated for fibulin-2 binding to nidogen and fibronectin high equilibrium dissociation constants (0.5 to 1 mu M) due to a rapid ini tial dissociation of the complexes. This is apparently followed by a s lower stabilizing reaction. The fibulin-2 binding site of nidogen coul d he localized to its C-terminal globular domain G3, which also posses ses a high-affinity binding site for laminin-1. Several tests demonstr ated competition between the two ligands, probably due to steric hindr ance. Binding of nidogen to immobilized fibulin-2 allowed the formatio n of ternary complexes with collagen IV, perlecan and fibulin-1, which , as shown previously, bind independently of the G3 domain. This indic ated multifunctional binding properties for fibulin-2 and several alte rnative routes for its integration into basement membranes and other e xtracellular structures. (C) 1995 Academic Press Limited