Laboratory of Microbial Physiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 7, 9747 AG Groningen, the Netherlands.
Laboratory of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 7, 9747 AG Groningen, the Netherlands.
Structure. 2017 Feb 7;25(2):231-242. doi: 10.1016/j.str.2016.11.023. Epub 2017 Jan 5.
Food processing and refining has dramatically changed the human diet, but little is known about whether this affected the evolution of enzymes in human microbiota. We present evidence that glycoside hydrolase family 70 (GH70) glucansucrases from lactobacilli, synthesizing α-glucan-type extracellular polysaccharides from sucrose, likely evolved from GH13 starch-acting α-amylases, via GH70 4,6-α-glucanotransferases. The crystal structure of a 4,6-α-glucanotransferase explains the mode of action and unique product specificity of these enzymes. While the α-amylase substrate-binding scaffold is retained, active-site loops adapted to favor transglycosylation over hydrolysis; the structure also gives clues as to how 4,6-α-glucanotransferases may have evolved further toward sucrose utilization instead of starch. Further supported by genomic, phylogenetic, and in vivo studies, we propose that dietary changes involving starch (and starch derivatives) and sucrose intake were critical factors during the evolution of 4,6-α-GTs and glucansucrases from α-amylases, allowing oral bacteria to produce extracellular polymers that contribute to biofilm formation from different substrates.
食品加工和精炼极大地改变了人类的饮食，但人们对这种变化是否影响了人类微生物群中酶的进化知之甚少。我们提供的证据表明，来自乳杆菌的糖苷水解酶家族 70（GH70）葡聚糖蔗糖酶通过 GH70 4,6-α-葡聚糖转移酶，可能从作用于 GH13 淀粉的 α-淀粉酶进化而来，用于从蔗糖合成 α-葡聚糖型细胞外多糖。4,6-α-葡聚糖转移酶的晶体结构解释了这些酶的作用模式和独特的产物特异性。虽然保留了 α-淀粉酶的底物结合支架，但活性位点环适应于促进转糖苷而不是水解；该结构还为 4,6-α-葡聚糖转移酶如何进一步进化为利用蔗糖而不是淀粉提供了线索。进一步的基因组、系统发育和体内研究支持了我们的观点，即涉及淀粉（和淀粉衍生物）和蔗糖摄入的饮食变化是 4,6-α-GTs 和葡聚糖蔗糖酶从 α-淀粉酶进化的关键因素，使口腔细菌能够产生有助于不同底物生物膜形成的细胞外聚合物。
