Kassoumi Konstantina, Kousoulou Penny, Sevastos Dimitrios, Vamvakas Sotirios-Spyridon, Papadimitriou Konstantinos, Kapolos John, Koliadima Athanasia
Department of Chemistry, University of Patras, 26504 Patras, Greece.
Department of Nutritional Science and Dietetics, University of the Peloponnese, 24100 Kalamata, Greece.
Foods. 2022 Jan 31;11(3):413. doi: 10.3390/foods11030413.
Winemaking is a stressful procedure for yeast cells. The presence of high levels of carbohydrates at the beginning of the fermentation and the subsequent increase of ethanol levels alongside with other environmental factors force the cell to undergo a continuous adaptation process. Ideally, yeast strains should be able to adapt to this changing environment fast and they must be able to ferment at low temperatures with the highest possible fermentation rates. Additionally, the balanced utilization of glucose and fructose-the two major hexoses in grapes-is also important as any residual fructose may confers unwanted sweetness. As proteins, Msn2/4 are known to play pivotal roles in cell stress response, the question that arise regards the differentially cell response driven by specific point mutations in these two proteins, and the subsequent effects on alcoholic fermentation. Four different mutants in which serine residues have been replaced by alanine are studied in this paper. Our results indicate that substitution at position 533 of Msn4 protein (W_M4_533) significantly increases the fermentation rate even at low temperatures (12 °C), by lowering the fermentation's activation energy. Similar results but to a lesser extent were obtained by the S582A substitution in Msn2 protein. In addition, W_M4_533 seems to have a more balanced utilization of must hexoses. From the present work it is concluded that genetic modification Msn2/4 represents a promising procedure for shortening the fermentation time, even at low temperatures, which in many cases constitutes an important technological requirement.
酿酒对酵母细胞来说是一个压力重重的过程。发酵开始时高含量碳水化合物的存在，以及随后乙醇含量的增加和其他环境因素，迫使细胞经历持续的适应过程。理想情况下，酵母菌株应能够快速适应这种不断变化的环境，并且必须能够在低温下以尽可能高的发酵速率进行发酵。此外，平衡利用葡萄糖和果糖（葡萄中的两种主要己糖）也很重要，因为任何残留的果糖都可能带来不必要的甜味。作为蛋白质，Msn2/4已知在细胞应激反应中起关键作用，由此产生的问题是这两种蛋白质中的特定点突变所驱动的细胞反应差异，以及对酒精发酵的后续影响。本文研究了四个丝氨酸残基被丙氨酸取代的不同突变体。我们的结果表明，Msn4蛋白第533位的取代（W_M4_533）通过降低发酵的活化能，即使在低温（12℃）下也能显著提高发酵速率。Msn2蛋白中的S582A取代也得到了类似但程度较小的结果。此外，W_M4_533似乎对葡萄汁中的己糖有更平衡的利用。从目前的工作可以得出结论，对Msn2/4进行基因改造是缩短发酵时间的一个有前景的方法，即使在低温下也是如此，而在许多情况下，低温是一项重要的技术要求。
