Park K H, Kim T J, Cheong T K, Kim J W, Oh B H, Svensson B
Research Center for New Bio-Materials in Agriculture and Department of Food Science and Technology, Seoul National University, Suwon, South Korea.
Biochim Biophys Acta. 2000 May 23;1478(2):165-85. doi: 10.1016/s0167-4838(00)00041-8.
Cyclomaltodextrinase (CDase, EC 3.2.1.54), maltogenic amylase (EC 3. 2.1.133), and neopullulanase (EC 3.2.1.135) are reported to be capable of hydrolyzing all or two of the following three types of substrates: cyclomaltodextrins (CDs); pullulan; and starch. These enzymes hydrolyze CDs and starch to maltose and pullulan to panose by cleavage of alpha-1,4 glycosidic bonds whereas alpha-amylases essentially lack activity on CDs and pullulan. They also catalyze transglycosylation of oligosaccharides to the C3-, C4- or C6-hydroxyl groups of various acceptor sugar molecules. The present review surveys the biochemical, enzymatic, and structural properties of three types of such enzymes as defined based on the substrate specificity toward the CDs: type I, cyclomaltodextrinase and maltogenic amylase that hydrolyze CDs much faster than pullulan and starch; type II, Thermoactinomyces vulgaris amylase II (TVA II) that hydrolyzes CDs much less efficiently than pullulan; and type III, neopullulanase that hydrolyzes pullulan efficiently, but remains to be reported to hydrolyze CDs. These three types of enzymes exhibit 40-60% amino acid sequence identity. They occur in the cytoplasm of bacteria and have molecular masses from 62 to 90 kDa which are slightly larger than those of most alpha-amylases. Multiple amino acid sequence alignment and crystal structures of maltogenic amylase and TVA II reveal the presence of an N-terminal extension of approximately 130 residues not found in alpha-amylases. This unique N-terminal domain as seen in the crystal structures apparently contributes to the active site structure leading to the distinct substrate specificity through a dimer formation. In aqueous solution, most of these enzymes show a monomer-dimer equilibrium. The present review discusses the multiple specificity in the light of the oligomerization and the molecular structures arriving at a clarified enzyme classification. Finally, a physiological role of the enzymes is proposed.
环麦芽糊精酶（CDase，EC 3.2.1.54）、产麦芽淀粉酶（EC 3.2.1.133）和新普鲁兰酶（EC 3.2.1.135）据报道能够水解以下三种底物中的全部或两种：环麦芽糊精（CDs）、普鲁兰多糖和淀粉。这些酶通过裂解α-1,4糖苷键将CDs和淀粉水解为麦芽糖，将普鲁兰多糖水解为潘糖，而α-淀粉酶对CDs和普鲁兰多糖基本没有活性。它们还催化寡糖向各种受体糖分子的C3-、C4-或C6-羟基进行转糖基化反应。本综述考察了基于对CDs的底物特异性定义的三种此类酶的生化、酶学和结构特性：I型，即环麦芽糊精酶和产麦芽淀粉酶，它们水解CDs的速度比水解普鲁兰多糖和淀粉快得多；II型，即普通嗜热放线菌淀粉酶II（TVA II），其水解CDs的效率远低于水解普鲁兰多糖；III型，即新普鲁兰酶，它能有效水解普鲁兰多糖，但尚未报道其能水解CDs。这三种酶的氨基酸序列一致性为40%-60%。它们存在于细菌细胞质中，分子量在62至90 kDa之间，略大于大多数α-淀粉酶。产麦芽淀粉酶和TVA II的多氨基酸序列比对及晶体结构显示存在一个约130个残基的N端延伸，这在α-淀粉酶中未发现。晶体结构中所见的这个独特的N端结构域显然通过二聚体形成对活性位点结构有贡献，并导致独特的底物特异性。在水溶液中，这些酶大多呈现单体-二聚体平衡。本综述根据寡聚化和分子结构讨论了多重特异性，得出了明确的酶分类。最后，提出了这些酶的生理作用。
