Biglycan and decorin bind close to the N-terminal region of the collagen VI triple helix

The binding of native biglycan and decorin to pepsin-extracted collagen VT from human placenta was examined by solid phase assay and by measurement of surface plasmon resonance in the BIAcore (TM) 2000 system. Both proteoglyc ans exhibited a strong affinity for collagen VI with dissociation constants (K-D) of similar to 30 nM. Removal of the glycosaminoglycan chains by chon droitinase ABC digestion did not significantly affect binding. In coprecipi tation experiments, biglycan and decorin bound to collagen VT and equally c ompeted with the other, suggesting that biglycan and decorin bind to the sa me binding site on collagen VI. This was confirmed by electron microscopy a fter negative staining of complexes between gold-labeled proteoglycans and collagen VI, demonstrating that both biglycan and decorin bound exclusively to a domain close to the interface between the N terminus of the triple he lical region and the following globular domain. In solid phase assay using recombinant collagen VI fragments, it was shown that the alpha2(VI) chain p robably plays a role in the interaction.