Evolution of family 18 glycoside hydrolases: diversity, domain structures and phylogenetic relationships.

Chitin and its derivates have many industrial and medical uses. There is a demand for chitin-modifying enzymes with new or modified properties and as microorganisms are the primary degraders of chitin in the environment, they provide a source of chitin-modifying enzymes with novel properties. We have analyzed the diversity, domain structure and phylogenetic relationships between family 18 chitinases based on complete genome sequences of bacteria, archaea, viruses, fungi, plants and animals. Our study shows that family 18 chitinases are divided into three main clusters, A, B and C. Clusters A and B both contain family 18 chitinases from bacteria, fungi and plants, suggesting that the differentiation of cluster A and B chitinases preceded the appearance of the eukaryotic lineage. Subgroups within clusters can have specific domain structures, as well as specific amino acid replacements in catalytic sites, which imply functional adaptation. This work provides a comprehensive overview of the evolutionary relationships of family 18 chitinases and provides a context for further investigations on functional aspects of family 18 chitinases in ecology and biotechnology.