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首页> 外文期刊>Applied Microbiology >4,6-α-Glucanotransferase, a Novel Enzyme That Structurally and Functionally Provides an Evolutionary Link between Glycoside Hydrolase Enzyme Families 13 and 70
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4,6-α-Glucanotransferase, a Novel Enzyme That Structurally and Functionally Provides an Evolutionary Link between Glycoside Hydrolase Enzyme Families 13 and 70

机译：4,6-α-葡萄糖基转移酶，一种新型酶，在结构和功能上提供了糖苷水解酶家族13和70之间的进化联系

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Lactobacillus reuteri 121 uses the glucosyltransferase A (GTFA) enzyme to convert sucrose into large amounts of the α-d-glucan reuteran, an exopolysaccharide. Upstream of gtfA lies another putative glucansucrase gene, designated gtfB . Previously, we have shown that the purified recombinant GTFB protein/enzyme is inactive with sucrose. Various homologs of gtfB are present in other Lactobacillus strains, including the L. reuteri type strain, DSM 20016, the genome sequence of which is available. Here we report that GTFB is a novel α-glucanotransferase enzyme with disproportionating (cleaving α1→4 and synthesizing α1→6 and α1→4 glycosidic linkages) and α1→6 polymerizing types of activity on maltotetraose and larger maltooligosaccharide substrates (in short, it is a 4,6-α-glucanotransferase). Characterization of the types of compounds synthesized from maltoheptaose by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS), methylation analysis, and 1-dimensional ~(1)H nuclear magnetic resonance (NMR) spectroscopy revealed that only linear products were made and that with increasing degrees of polymerization (DP), more α1→6 glycosidic linkages were introduced into the final products, ranging from 18% in the incubation mixture to 33% in an enriched fraction. In view of its primary structure, GTFB clearly is a member of the glycoside hydrolase 70 (GH70) family, comprising enzymes with a permuted (β/α)_(8) barrel that use sucrose to synthesize α-d-glucan polymers. The GTFB enzyme reaction and product specificities, however, are novel for the GH70 family, resembling those of the GH13 α-amylase type of enzymes in using maltooligosaccharides as substrates but differing in introducing a series of α1→6 glycosidic linkages into linear oligosaccharide products. We conclude that GTFB represents a novel evolutionary intermediate between the GH13 and GH70 enzyme families, and we speculate about its origin.
机译：罗伊氏乳杆菌121使用葡萄糖基转移酶A（GTFA）酶将蔗糖转化为大量的α-d-葡聚糖reuteran（一种胞外多糖）。 gtfA的上游还有另一个推定的葡聚糖酶基因，称为gtfB。以前，我们已经表明纯化的重组GTFB蛋白/酶对蔗糖没有活性。 gtfB的各种同源物存在于其他乳酸杆菌菌株中，包括罗伊氏乳杆菌型菌株DSM 20016，其基因组序列可用。在这里，我们报道GTFB是一种新颖的α-葡聚糖转移酶，具有歧化作用（裂解α1→4并合成α1→6和α1→4糖苷键），并且在麦芽四糖和较大的麦芽低聚糖底物上（简而言之，它是是4,6-α-葡聚糖转移酶）。通过基质辅助激光解吸电离-飞行时间质谱（MALDI-TOF MS），甲基化分析和一维〜（1）H核磁共振（NMR）光谱对麦芽七糖合成的化合物类型进行表征仅制备线性产物，并且随着聚合度（DP）的增加，最终产物中引入了更多的α1→6糖苷键，从孵化混合物中的18％到富集级分的33％。鉴于其一级结构，GTFB显然是糖苷水解酶70（GH70）家族的成员，其中包含具有排列排列的（β/α）_（8）桶的酶，该酶使用蔗糖合成α-d-葡聚糖聚合物。但是，对于GH70家族，GTFB酶的反应和产物特异性是新颖的，类似于使用麦芽低聚糖作为底物的GH13α-淀粉酶类型的酶，但是在将一系列α1→6糖苷键引入线性低聚糖产物方面有所不同。我们得出的结论是，GTFB代表GH13和GH70酶家族之间的新型进化中间体，我们推测其起源。

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