Binding of the G domains of laminin α1 and α2 chains and perlecan to heparin, sulfatides, α-dystroglycan and several extracellular matrix proteins

The C-terminal G domain of the mouse laminin alpha 2 chain consists of five lamin-type G domain (LG) modules (alpha 2LG1 to alpha 2LG5) and was obtained as several recombinant fragments, corresponding to either individual modules or the tandem arrays alpha 2LG1-3 and alpha 2LG4-5, These fragments were compared with similar modules from the laminin al chain and from the C-terminal region of perlecan (PGV) in several binding studies. Major heparin-binding sites were located on the two tandem fragments and the individual alpha 2LG1, alpha 2LG3 and alpha 2LG5 modules. The binding epitope on alpha 2LG5 could be localized to a cluster of lysines by site-directed mutagenesis. In the alpha 1 chain, however, strong heparin binding was found on alpha 1LG4 and not on alpha 1LG5, Binding to sulfatides correlated to heparin binding in most but not all cases. Fragments alpha 2LG1-3 and alpha 2LG4-5 also bound to fibulin-1, fibulin-2 and nidogen-2 with K-d = 13-150 nM. Both tandem fragments, but not the individual modules, bound strongly to alpha-dystroglycan and this interaction was abolished by EDTA but not by high concentrations of heparin and NaCl. The binding of perlecan fragment PGV to alpha-dystroglycan was even stronger and was also not sensitive to heparin, This demonstrated similar binding repertoires for the LG modules of three basement membrane proteins involved in cell-matrix interactions and supramolecular assembly.