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首页> 美国卫生研究院文献>The Journal of Biological Chemistry >Structural analysis of group II chitinase (ChtII) catalysis completes the puzzle of chitin hydrolysis in insects
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Structural analysis of group II chitinase (ChtII) catalysis completes the puzzle of chitin hydrolysis in insects

机译：II类几丁质酶（ChtII）催化的结构分析完成了昆虫中几丁质水解的难题

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Chitin is a linear homopolymer of N-acetyl-β-d-glucosamines and a major structural component of insect cuticles. Chitin hydrolysis involves glycoside hydrolase family 18 (GH18) chitinases. In insects, chitin hydrolysis is essential for periodic shedding of the old cuticle ecdysis and proceeds via a pathway different from that in the well studied bacterial chitinolytic system. Group II chitinase (ChtII) is a widespread chitinolytic enzyme in insects and contains the greatest number of catalytic domains and chitin-binding domains among chitinases. In Lepidopterans, ChtII and two other chitinases, ChtI and Chi-h, are essential for chitin hydrolysis. Although ChtI and Chi-h have been well studied, the role of ChtII remains elusive. Here, we investigated the structure and enzymology of OfChtII, a ChtII derived from the insect pest Ostrinia furnacalis. We present the crystal structures of two catalytically active domains of OfChtII, OfChtII-C1 and OfChtII-C2, both in unliganded form and complexed with chitooligosaccharide substrates. We found that OfChtII-C1 and OfChtII-C2 both possess long, deep substrate-binding clefts with endochitinase activities. OfChtII exhibited structural characteristics within the substrate-binding cleft similar to those in OfChi-h and OfChtI. However, OfChtII lacked structural elements favoring substrate binding beyond the active sites, including an extra wall structure present in OfChi-h. Nevertheless, the numerous domains in OfChtII may compensate for this difference; a truncation containing one catalytic domain and three chitin-binding modules (OfChtII-B4C1) displayed activity toward insoluble polymeric substrates that was higher than those of OfChi-h and OfChtI. Our observations provide the last piece of the puzzle of chitin hydrolysis in insects.
机译：甲壳质是N-乙酰基-β-d-葡萄糖胺的线性均聚物，是昆虫表皮的主要结构成分。几丁质水解涉及糖苷水解酶家族18（GH18）几丁质酶。在昆虫中，几丁质水解对于定期脱落旧的角质层蜕皮至关重要，其水解途径与经过充分研究的细菌几丁质分解系统不同。 II族几丁质酶（ChtII）是昆虫中广泛的几丁质分解酶，并且在几丁质酶中包含最大数量的催化结构域和几丁质结合结构域。在鳞翅目中，ChtII和另外两个几丁质酶ChtI和Chi-h对几丁质水解至关重要。尽管已经对ChtI和Chi-h进行了深入研究，但ChtII的作用仍然难以捉摸。在这里，我们调查了OfChtII的结构和酶学，OfChtII是一种源自昆虫害虫Ostrinia furnacalis的ChtII。我们介绍了OfChtII，OfChtII-C1和OfChtII-C2的两个催化活性域的晶体结构，无论是未配体形式还是与壳寡糖底物复合。我们发现OfChtII-C1和OfChtII-C2都具有带有内切壳多糖酶活性的长而深的底物结合裂口。 OfChtII在底物结合裂隙内表现出与OfChi-h和OfChtI类似的结构特征。但是，OfChtII缺乏有利于活性位点以外的底物结合的结构元素，包括OfChi-h中存在的额外壁结构。但是，OfChtII中的众多域可以弥补这一差异。包含一个催化结构域和三个几丁质结合模块（OfChtII-B4C1）的截短物显示出对不溶性聚合物底物的活性，其活性高于OfChi-h和 Of ChtI。我们的观察提供了甲壳素在昆虫中水解的最后难题。

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