Glycobiology Advance Access originally published online on September 6, 2006
Glycobiology 2006 16(12):1242-1250; doi:10.1093/glycob/cwl043
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Rice chitinases: sugar recognition specificities of the individual subsites
2 Present address: National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan
3 Department of Advanced Bioscience, Kinki University, 3327-204 Nakamachi, Nara 631-8505, Japan;
4 Norwegian Biopolymer Laboratory (NOBIPOL), Department of Biotechnology, Norwegian University of Science and Technology, Sem Sælands vei 6/8 N-7491 Trondheim, Norway; and
5 Akita Research Institute of Food and Brewing (ARIF), 4-26 Aza-sanuki, Arayamachi, Akita 010-1623, Japan
1 To whom correspondence should be addressed; e-mail: fukamizo{at}nara.kindai.ac.jp
Received on May 31, 2006; revised on August 28, 2006; accepted on August 28, 2006
Sugar recognition specificities of class III (OsChib1a) and class I (OsChia1c
ChBD) chitinases from rice, Oryza sativa L., were investigated by analyzing 1H- and 13C-nuclear magnetic resonance spectra of the enzymatic products from partially N-acetylated chitosans. The reducing end residue of the enzymatic products obtained by the class III enzyme was found to be exclusively acetylated, whereas both acetylated and deacetylated units were found at the nearest neighbor to the reducing end residue. Both acetylated and deacetylated units were also found at the nonreducing end residue and its nearest neighbor of the class III enzyme products. Thus, only subsite (–1) among the contiguous subsites (–2) to (+2) of the class III enzyme was found to be specific to an acetylated residue. For the class I enzyme, the reducing end residue was preferentially acetylated, although the specificity was not absolute. The nearest neighbor to the acetylated reducing end residue was specifically acetylated. Moreover, the nonreducing end residue produced by the class I enzyme was exclusively acetylated, although there was a low but significant preference for deacetylated units at the nearest neighbor to the nonreducing end. These results suggest that the three contiguous subsites (–2), (–1), and (+1) of the class I enzyme are specific to three consecutive GlcNAc residues of the substrate. In rice plants, the target of the class I enzyme might be a consecutive GlcNAc sequence probably in the cell wall of fungal pathogen, whereas the class III enzyme might act toward an endogenous complex carbohydrate containing GlcNAc residue.
Key words: chitinase / Oryza sativa L / partially N-acetylated chitosan / specificity / subsites