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.