Fibronectin type III-like sequences and a new domain type in prokaryotic depolymerases with insoluble substrates.

Fibronectin type III-like sequences are present in many proteins from higher eukaryotes and are involved in protein-protein interactions, heparin binding and cell adhesion. A nine-member family of bacterial sequences is shown to be significantly homologous to the type III-like sequences. All the sequences are contained in secreted depolymerases acting on complex, energy-rich insoluble substrates, in which they apparently do not participate in catalysis or substrate-binding, their exact function remaining unclear. Furthermore, a new family of sequences, present in some cellulases, is presented.