Crystal structures of substrate-bound chitinase from the psychrophilic bacteriumMoritella marinaand its structure in solution

Abstract

The four-domain structure of chitinase 60 fromMoritella marina(MmChi60) is outstanding in its complexity. Many glycoside hydrolases, such as chitinases and cellulases, have multi-domain structures, but only a few have been solved. The flexibility of the hinge regions between the domains apparently makes these proteins difficult to crystallize. The analysis of an active-site mutant ofMmChi60 in an unliganded form and in complex with the substrates NAG4and NAG5revealed significant differences in the substrate-binding site compared with the previously determined complexes of most studied chitinases. A SAXS experiment demonstrated that in addition to the elongated state found in the crystal, the protein can adapt other conformations in solution ranging from fully extended to compact.