Crystal structure of chitin binding domain of chitinase A1

Takanori Matsuuraa, Izumi Yabutaa, Tohru Yamaguchb, Eriko Chikaishia, Yuko Nagasakic, Masashi Harac, Takeshi Watanabec, Kenichi Akagia, Hideo Akutsua, Takahisa Ikegamia and Atsushi Nakagawaa

aInstitute for Protein Research, Osaka University
bDiscovery Research Laboratories, Shionogi & Co., Ltd.
cFaculty of Agriculture, Niigata University

XX Congress of the International Union of Crystallography (Florence, Italy, 2005.8.23-31)

The crystal structure of the chitin-binding domain (ChBD) of chitinase A1 (ChiA1) from B. circulans WL-12 has been determined. ChiA1 is a glycosidase that hydrolyzes chitin, and ChBD, ranging from Ala655 to Gln699 located at the C-terminal, binds specifically to insoluble chitin.

The diffraction data of the ChBDChiA1 crystal were collected at BL44XU at SPring-8, Japan, with the resolution of 0.95 Å. The phase was determined by the molecular replacement method using the structure previously determined by NMR as the model.

ChBDChiA1 has a compact and globular structure with the topology of a twisted β-sandwich. The overall topology is similar to that of the cellulose-binding domain (CBD) of Erwinia chrysanthemi endoglucanase Z (CBDEGZ). However, ChBDChiA1 lacks the three aromatic residues (Trp18, Trp43, and Tyr44 in CBDEGZ), aligned linearly and exposed to the solvent, which interact with cellulose. Mutation studies suggested that the loop region containing Trp687 interact with chitin. Moreover, ChBDChiA1 is detached from chitin by decreasing the pH value in solution from 4 to 3, probably because the charge in the side-chain of Glu688 is involved in the chitin-binding. Therefore, the binding mechanism of ChBDChiA1 is expected to be different from that proposed for CBDs.

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MATSUURA Takanori (Please change the mark “%” to “@”)

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