Structure and function of chitinases from glycoside hydrolase family 19

Glycoside hydrolase family 19 chitinases are found in plants, bacteria and viruses, playing various roles. Plant chitinases are important for defence and development, whereas bacterial examples are useful for nutrition. The available structural studies show that family 19 enzymes are highly α‐helical bi‐lobed structures with a wide cleft lined by conserved residues important for catalysis and substrate binding. Class I and II plant chitinases possess loops which are absent in class IV and/or bacterial chitinases. One of the loops seems to retain a significant function. These inverting endochitinases demonstrate a possible opening–closing mechanism of the catalytic cleft during chitin hydrolysis due to loop movements. However, complex structures with inhibitors and/or substrate/product analogues are required for a deeper understanding of these enzymes.