Starch produced by plants is a stored form of energy and is an important dietary source of calories for humans and domestic animals. Disproportionating enzyme (D‐enzyme) catalyzes intramolecular and intermolecular transglycosylation reactions of α‐1, 4‐glucan. D‐enzyme is essential in starch metabolism in the potato. We present the crystal structures of potato D‐enzyme, including two different types of complex structures: a primary Michaelis complex (substrate binding mode) for 26‐meric cycloamylose (CA26) and a covalent intermediate for acarbose. Our study revealed that the acarbose and CA26 reactions catalyzed by potato D‐enzyme involve the formation of a covalent intermediate with the donor substrate. HPAEC of reaction substrates and products revealed the activity of the potato D‐enzyme on acarbose and CA26 as donor substrates. The structural and chromatography analyses provide insight into the mechanism of the coupling reaction of CA and glucose catalyzed by the potato D‐enzyme. The enzymatic reaction mechanism does not involve residual hydrolysis. This could be particularly useful in preventing unnecessary starch degradation leading to reduced crop productivity. Optimization of this mechanism would be important for improvements of starch storage and productivity in crops.

中文翻译：

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马铃薯歧化酶（D-酶）的结构分析及反应机理。


植物产生的淀粉是能量的储存形式，是人类和家畜热量的重要膳食来源。歧化酶（D-酶）催化α-1, 4-葡聚糖的分子内和分子间转糖基反应。 D-酶对于马铃薯的淀粉代谢至关重要。我们展示了马铃薯 D-酶的晶体结构，包括两种不同类型的复合物结构：26 聚环直链淀粉 (CA26) 的初级米氏复合物（底物结合模式）和阿卡波糖的共价中间体。我们的研究表明，马铃薯 D 酶催化的阿卡波糖和 CA26 反应涉及与供体底物形成共价中间体。反应底物和产物的 HPAEC 揭示了马铃薯 D 酶对阿卡波糖和 CA26 作为供体底物的活性。结构和色谱分析有助于深入了解马铃薯 D 酶催化的 CA 和葡萄糖的偶联反应机制。酶促反应机理不涉及残余水解。这对于防止不必要的淀粉降解导致作物生产力下降特别有用。该机制的优化对于提高作物淀粉储存和生产力非常重要。