Department of Microbiology, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India.
Appl Microbiol Biotechnol. 2016 Jul;100(13):5661-79. doi: 10.1007/s00253-016-7572-y. Epub 2016 May 3.
Pullulan hydrolyzing enzymes are endoacting, classified based on the substrate specificity and hydrolysis products as pullulanases (type I and II) and pullulan hydrolases (type I, II and III). Pullulanases and pullulan hydrolase type I are produced by bacteria and archaea. Among bacteria, many mesophilic, thermophilic and hyperthermophilic bacteria produce pullulanases and neopullulanases. While pullulan hydrolase type II and type III are produced by fungi and archaea, respectively. These are multi-domain proteins with three conserved catalytic acidic residues of the glycosyl hydrolases. The recent advances in molecular biology and protein engineering via mutagenesis and truncation led to improvement in thermostability, catalytic activity and substrate specificity. Pullulanases are debranching enzymes, which are widely employed in starch saccharification that minimizes the use of glucoamylase (approx. 50 %) and reduces the total reaction time of the industrial starch conversion process. The thermostable amylopullulanases are useful in one-step starch liquefaction and saccharification, which replaces amylolytic enzymes like α-amylase and glucoamylase, thus resulting in the reduction in the cost of sugar production. The enzymes also find application in making resistant starches and as an antistale in bread making. Panose and isopanose containing syrups are useful as prebiotics, while panose has also been reported to display anticarcinogenic activity. This review focuses on the distinguishing features of these enzymes based on the analysis of amino acid sequences and domain structure, besides highlighting recent advances in the molecular biology and protein engineering for enhancing their thermostability, catalytic activity and substrate specificity. This review also briefly summarizes the potential applications of pullulanases and pullulan hydrolases.
普鲁兰水解酶为内切酶，根据底物特异性和水解产物的不同，可分为普鲁兰酶（I 型和 II 型）和普鲁兰水解酶（I、II 和 III 型）。普鲁兰酶和普鲁兰水解酶 I 型由细菌和古菌产生。在细菌中，许多嗜温菌、嗜热菌和超嗜热菌产生普鲁兰酶和新普鲁兰酶。而普鲁兰水解酶 II 型和 III 型分别由真菌和古菌产生。这些酶都是多结构域蛋白，具有糖苷水解酶的三个保守催化酸性残基。通过突变和截短的分子生物学和蛋白质工程的最新进展，提高了它们的热稳定性、催化活性和底物特异性。普鲁兰酶是分枝酶，广泛应用于淀粉糖化，可最大程度减少使用糖化酶（约 50%），并缩短工业淀粉转化过程的总反应时间。热稳定的支链淀粉普鲁兰酶在一步法淀粉液化和糖化中非常有用，它取代了α-淀粉酶和糖化酶等淀粉水解酶，从而降低了糖生产的成本。这些酶还可用于制造抗性淀粉和作为面包制作中的抗老化剂。含有潘糖和异潘糖的糖浆可用作益生元，而潘糖也被报道具有抗癌活性。本综述重点介绍了这些酶基于氨基酸序列和结构域分析的区别特征，同时强调了分子生物学和蛋白质工程方面的最新进展，以提高它们的热稳定性、催化活性和底物特异性。本文还简要总结了普鲁兰酶和普鲁兰水解酶的潜在应用。
