Fibronectin binding to complement subcomponent C1q. Localization of their respective binding sites.
The interaction of purified human plasma fibronectin with the C1q subcomponent of complement was investigated by using a solid-phase radiobinding assay. 125I-fibronectin binding to native C1q, purified collagen domain (C1q-c) or globular domain (C1q-g) was compared. When the purified domains were insolubilized by binding to plastic, the C1q-c exhibited 59% of the binding demonstrated with intact C1q, whereas the C1q-g exhibited 35% of the binding. N-Terminal sequencing of the globular domain showed that a sequence of seven collagen-like amino acids was retained on each chain of the C1q-g fragment. 125I-fibronectin binding to C1q could be inhibited equally well by fluid-phase C1q and C1q-c, but not by fluid-phase C1q-g, implying that the collagen-like region retained on the C1q-g is masked in the fluid phase. In addition, studies were performed to determine which subunit(s) of C1q bind(s) fibronectin. The percentages of fibronectin bound by the A, B, and C chain of C1q were found to be 38, 21 and 41% respectively. Inhibition studies with purified 200-180 kDa, 50 kDa or 29 kDa fragments of fibronectin show that the binding site on fibronectin for C1q is the 50 kDa gelatin-binding domain.
D000595:Amino Acid Sequence; D001665:Binding Sites; D003166:Complement Activating Enzymes / Q000276:immunology*; D015922:Complement C1q; D004591:Electrophoresis, Polyacrylamide Gel; D005353:Fibronectins / Q000276:immunology*; D006801:Humans; D010446:Peptide Fragments / Q000276:immunology
D005353:Fibronectins; D010446:Peptide Fragments; D015922:Complement C1q; D003166:Complement Activating Enzymes