Abstract:Fibronectin is a large cell adhesion molecule that is composed of several functional domains. The cell-binding domain that binds to cell surface integrins consists of repeated homologous type 111 modules. In this study, recombinant fragments from the cell-binding domain of human fibronectin that participate in a newly characterized fibronectin-fibronectin interaction with FNIII I were crystallized. In each case, the crystals had more than one fibronectin fragment in the asymmetric unit. Crystals of F N I I I l o~l , grew in the space group C2 with a = 117.1 A, b = 38.6 A, c = 80.6 A, /3 = 97.2", and two molecules in the asymmetric unit.These crystals diffracted to 2.5 8, resolution. Fragment FNIII,-, and a shorter fragment, FNIIIx-,o, crystallized in hexagonal space groups with large unit cells and two to four molecules per asymmetric unit. Even very large crystals of these fragments did not diffract beyond 4 A. The crystal packing for this collection of fibronectin fragments suggests conformational flexibility between linked type 111 modules. The functional relevance of this flexibility for elongated versus compact models of the cell-binding domain of fibronectin is discussed.