Complete subsite mapping of a “loopful” GH19 chitinase from rye seeds based on its crystal structure

Crystallographic analysis of a mutated form of “loopful” GH19 chitinase from rye seeds a double mutant RSC-c, in which Glu67 and Trp72 are mutated to glutamine and alanine, respectively, (RSC-c-E67Q/W72A) in complex with chitin tetrasaccharide (GlcNAc)4 revealed that the entire substrate-binding cleft was completely occupied with the sugar residues of two (GlcNAc)4 molecules. One (GlcNAc)4 molecule bound to subsites −4 to −1, while the other bound to subsites +1 to +4. Comparisons of the main chain conformation between liganded RSC-c-E67Q/W72A and unliganded wild type RSC-c suggested domain motion essential for catalysis. This is the first report on the complete subsite mapping of GH19 chitinase.