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

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Abstract
The C‐terminal G domain of the mouse laminin α2 chain consists of five lamin‐type G domain (LG) modules (α2LG1 to α2LG5) and was obtained as several recombinant fragments, corresponding to either individual modules or the tandem arrays α2LG1‐3 and α2LG4‐5. These fragments were compared with similar modules from the laminin α1 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 α2LG1, α2LG3 and α2LG5 modules. The binding epitope on α2LG5 could be localized to a cluster of lysines by site‐directed mutagenesis. In the α1 chain, however, strong heparin binding was found on α1LG4 and not on α1LG5. Binding to sulfatides correlated to heparin binding in most but not all cases. Fragments α2LG1–3 and α2LG4‐5 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 α‐dystroglycan and this interaction was abolished by EDTA but not by high concentrations of heparin and NaCl. The binding of perlecan fragment PGV to α‐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.