CBMA - Center of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal.
Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
Sci Rep. 2021 Feb 26;11(1):4766. doi: 10.1038/s41598-021-83937-z.
Carbohydrate rich substrates such as lignocellulosic hydrolysates remain one of the primary sources of potentially renewable fuel and bulk chemicals. The pentose sugar D-xylose is often present in significant amounts along with hexoses. Saccharomyces cerevisiae can acquire the ability to metabolize D-xylose through expression of heterologous D-xylose isomerase (XI). This enzyme is notoriously difficult to express in S. cerevisiae and only fourteen XIs have been reported to be active so far. We cloned a new D-xylose isomerase derived from microorganisms in the gut of the wood-feeding beetle Odontotaenius disjunctus. Although somewhat homologous to the XI from Piromyces sp. E2, the new gene was identified as bacterial in origin and the host as a Parabacteroides sp. Expression of the new XI in S. cerevisiae resulted in faster aerobic growth than the XI from Piromyces on D-xylose media. The D-xylose isomerization rate conferred by the new XI was also 72% higher, while absolute xylitol production was identical in both strains. Interestingly, increasing concentrations of xylitol (up to 8 g L) appeared not to inhibit D-xylose consumption. The newly described XI displayed 2.6 times higher specific activity, 37% lower K for D-xylose, and exhibited higher activity over a broader temperature range, retaining 51% of maximal activity at 30 °C compared with only 29% activity for the Piromyces XI.
富含碳水化合物的基质，如木质纤维素水解物，仍然是潜在可再生燃料和大宗化学品的主要来源之一。戊糖 D-木糖通常与己糖一起大量存在。酿酒酵母可以通过表达异源 D-木糖异构酶（XI）来获得代谢 D-木糖的能力。这种酶在酿酒酵母中表达非常困难，迄今为止只有 14 种 XI 被报道具有活性。我们克隆了一种新的 D-木糖异构酶，它来源于木质甲虫 Odontotaenius disjunctus 肠道中的微生物。尽管与来自 Piromyces sp. E2 的 XI 有些同源，但新基因被鉴定为细菌起源，宿主为 Parabacteroides sp. 在酿酒酵母中表达新的 XI 导致比在 D-木糖培养基上来自 Piromyces 的 XI 具有更快的需氧生长。新 XI 赋予的 D-木糖异构化速率也高 72%，而在两种菌株中绝对木糖醇产量相同。有趣的是，增加的木糖醇浓度（高达 8 g/L）似乎不会抑制 D-木糖的消耗。新描述的 XI 显示出 2.6 倍更高的比活性、37%更低的 D-木糖 K 值，并且在更宽的温度范围内表现出更高的活性，在 30°C 时保留 51%的最大活性，而 Piromyces XI 的活性仅为 29%。
