The crystal structure of the chitin binding domain of chitinase A1 from Bacillus circulans WL-12

Takanori Matsuura1, Izumi Yabuta1, Eriko Chikaishi1, Yuko Nagasaki2, Masashi Hara2, Takeshi Watanabe2, Kenichi Akagi1, Hideo Akutsu1, Takahisa Ikegami1 and Atsushi Nakagawa1

1Institute for Protein Research, Osaka University
2Department of Applied Biological Chemistry, Faculty of Agriculture, Niigata University

BSR2004 (the 8th International Conference on Biology and Synchrotron Radiation), (Himeji, Japan 2004.9.7-11)

The crystal structure of the chitin-binding domain (ChBD) of chitinase A1 (ChiA1) from Bacillus 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, which belongs to the space group of P2121211 with the cell dimensions of a=22.3, b=38.2, c=40.3 Å, were obtained 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 (J. Biol. Chem. 275 (2000) 13654).

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 have recently suggested that the loop region containing Trp687 be the interaction region with chitin (Biochim. Biophys. Acta 1621 (2003) 31 and Arch. Biochem. Biophys. 426 (2004) 286). 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, the next to Trp687, 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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