Fibronectin interacts with Clq, a subcomponent of the first component of complement.

Human Clq, a subcomponent of the first component of complement interacts with human fibronectin. Using ELISA methodology fixation of Clq to solid phase fibronectin, as well as fibronectin to solid phase Clq has been demonstrated. Cl in its native macromolecular form displays little reactivity for fibronectin, nor does Cl reconstituted from Clq, Clr and Cls in the presence of Ca2+ ions. Heating of Clq above its thermal transition temperature (51 degrees C) induces an increased binding capacity for fibronectin. On the other hand, a mixture of the dissociated A, B and C chains of Clq is less active than native Clq. The binding of fibronectin appears to be mediated by the A chain. Studies with Clq deprived of its globular parts by peptic digestion indicate that the collagen-like regions of Clq are involved in fibronectin binding. In contrast, collagenase treatment of Clq abrogates its fibronectin binding capacity.