This family consists of the N-terminal region of the prokaryotic fibronectin-binding protein. Fibronectin binding is considered to be an important virulence factor in streptococcal infections. Fibronectin is a dimeric glycoprotein that is present in a soluble form in plasma and extracellular fluids; it is also present in a fibrillar form on cell surfaces. Both the soluble and cellular forms of fibronectin may be incorporated into the extracellular tissue matrix. While fibronectin has critical roles in eukaryotic cellular processes, such as adhesion, migration and differentiation, it is also a substrate for the attachment of bacteria. The binding of pathogenic Streptococcus pyogenes and Staphylococcus aureus to epithelial cells via fibronectin facilitates their internalisation and systemic spread within the host.