Zinc Induces Structural Reorganization of Gelatin Binding Domain from Human Fibronectin and Affects Collagen Binding

Fibronectin is a modular extracellular matrix protein involved in cell adhesion, cell motility, wound healing, and maintenance of cell morphology. It is composed of multiple repeats of three distinct modules: F-I, F-II, and F-III. Various combinations of these modules create fragments able to interact with different constituents of the 0 extracellular matrix. Here, we present the 2.5-angstrom resolution crystal structure of its 45-kDa gelatin-binding domain (GBD; 6F(I)-1F(II)-2F(II)-7F(I)-8F(I)-9F(I)), which also corresponds to the C-terminal half of the migration stimulating factor, a Fn splice variant expressed in human breast cancers. GBD forms a very compact zinc-mediated homodimer, in stark contrast with previous structures of fibronectin fragments. Most remarkably, 8F(I) no longer adopts the canonical F-I fold but is composed of two long strands that associate with 7F(I) and 9F(I) into a large beta-sheet superdomain. Binding studies in solution confirmed that Zn induces conformational rearrangements and causes loss of binding of Fn-GBD to high-affinity collagen peptides. These data suggest the Zn may play a regulatory role for the cellular functions of fibronectin.