植物の自己防御タンパク質、キチナーゼの構造と機能に関する研究

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Yam aerial tuber chitinase, one of the inherent self defense protein, was purified and determined their protein structure and their localization in plant. For the purification, new method using quaternary ammonium ion detergent was developed. The purified chitinases were determined their amino acid sequences, which revealed that the high and low molecular weight isoforms were class I and class III chitinases, respectively. Further, the positions of S-S bonds of class I chitinase were determined. The determined positions were same as barley class II chitinase, but different from those of rye class II chitinase at C-terminal region. This indicates the flexibility at the C-terminal region. The structural relationships of plant chitinases were phylogenetically studied. The established protein genealogy showed the two subclasses in class I and class II chitinases. The high molecular weight subclass was estimated to be an ancestral molecule. No subclass was detected in class III chitinases. The localizations of yam class I and class III chitinases were immunohistochemically studied. The staining showed that the class I chitinase locates every young tissue and class III chitinase locates only tubers. This result indicates that these chitinases possess different defense role in plant.