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首页> 外文期刊>BMC Biotechnology >Physiological effects of over-expressing compartment-specific components of the protein folding machinery in xylose-fermenting Saccharomyces cerevisiae
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Physiological effects of over-expressing compartment-specific components of the protein folding machinery in xylose-fermenting Saccharomyces cerevisiae

机译：过表达木糖发酵酿酒酵母中蛋白质折叠机制的特定于隔室的成分的生理效应

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Background Efficient utilization of both glucose and xylose is necessary for a competitive ethanol production from lignocellulosic materials. Although many advances have been made in the development of xylose-fermenting strains of Saccharomyces cerevisiae , the productivity remains much lower compared to glucose. Previous transcriptional analyses of recombinant xylose-fermenting strains have mainly focused on central carbon metabolism. Very little attention has been given to other fundamental cellular processes such as the folding of proteins. Analysis of previously measured transcript levels in a recombinant XR/XDH-strain showed a wide down-regulation of genes targeted by the unfolded protein response during xylose fermentation. Under anaerobic conditions the folding of proteins is directly connected with fumarate metabolism and requires two essential enzymes: FADH2-dependent fumarate reductase (FR) and Ero1p. In this study we tested whether these enzymes impair the protein folding process causing the very slow growth of recombinant yeast strains on xylose under anaerobic conditions. Results Four strains over-expressing the cytosolic ( FRD1 ) or mitochondrial ( OSM1 ) FR genes and ERO1 in different combinations were constructed. The growth and fermentation performance was evaluated in defined medium as well as in a complex medium containing glucose and xylose. Over-expression of FRD1 , alone or in combination with ERO1 , did not have any significant effect on xylose fermentation in any medium used. Over-expression of OSM1 , on the other hand, led to a diversion of carbon from glycerol to acetate and a decrease in growth rate by 39% in defined medium and by 25% in complex medium. Combined over-expression of OSM1 and ERO1 led to the same diversion of carbon from glycerol to acetate and had a stronger detrimental effect on the growth in complex medium. Conclusions Increasing the activities of the FR enzymes and Ero1p is not sufficient to increase the anaerobic growth on xylose. So additional components of the protein folding mechanism that were identified in transcription analysis of UPR related genes may also be limiting. This includes i) the transcription factor encoded by HAC1 ii) the activity of Pdi1p and iii) the requirement of free FAD during anaerobic growth.
机译：背景技术从木质纤维素材料中竞争性生产乙醇必须有效利用葡萄糖和木糖。尽管在酿酒酵母的木糖发酵菌株的开发中已经取得了许多进展，但是与葡萄糖相比，生产率仍然低得多。重组木糖发酵菌株的先前转录分析主要集中在中央碳代谢上。其他基本的细胞过程，如蛋白质折叠，却很少受到关注。重组XR / XDH菌株中以前测得的转录水平的分析表明，木糖发酵过程中未折叠的蛋白质反应靶向的基因广泛下调。在厌氧条件下，蛋白质的折叠与富马酸酯的代谢直接相关，并且需要两种必需的酶：FADH 2 依赖性富马酸酯还原酶（FR）和Ero1p。在这项研究中，我们测试了这些酶是否会破坏蛋白质折叠过程，从而导致重组酵母菌株在厌氧条件下在木糖上的生长非常缓慢。结果构建了四种分别过量表达胞质（FRD1）或线粒体（OSM1）FR基因和ERO1的菌株。在限定的培养基以及含有葡萄糖和木糖的复杂培养基中评估生长和发酵性能。单独或与ERO1联合使用时，FRD1的过表达对所用任何培养基中的木糖发酵均无明显影响。另一方面，OSM1的过度表达导致碳从甘油转移到乙酸盐，并且在确定的培养基中生长速率降低了39％，在复杂的培养基中降低了25％。 OSM1和ERO1的联合过表达导致碳从甘油到乙酸的相同转移，并且对复杂培养基中的生长具有更强的有害作用。结论增加FR酶和Ero1p的活性不足以增加木糖上厌氧菌的生长。因此，在UPR相关基因的转录分析中鉴定出的蛋白质折叠机制的其他成分也可能受到限制。这包括：i）HAC1编码的转录因子; ii）Pdi1p的活性;以及iii）厌氧生长过程中对游离FAD的需求。

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