Role of Elm1, Tos3, and Sak1 Protein Kinases in the Maltose Metabolism of Baker's Yeast.

Xu Yang,Huan-Yuan Jiang,Lu Meng,Xiao-Ping Hu,Cong-Fa Li,Xue Lin

doi:10.3389/fmicb.2021.665261

Abstract

Glucose repression is a key regulatory system controlling the metabolism of non-glucose carbon source in yeast. Glucose represses the utilization of maltose, the most abundant fermentable sugar in lean dough and wort, thereby negatively affecting the fermentation efficiency and product quality of pasta products and beer. In this study, the focus was on the role of three kinases, Elm1, Tos3, and Sak1, in the maltose metabolism of baker’s yeast in lean dough. The results suggested that the three kinases played different roles in the regulation of the maltose metabolism of baker’s yeast with differential regulations on MAL genes. Elm1 was necessary for the maltose metabolism of baker’s yeast in maltose and maltose-glucose, and the overexpression of ELM1 could enhance the maltose metabolism and lean dough fermentation ability by upregulating the transcription of MALx1 (x is the locus) in maltose and maltose-glucose and MALx2 in maltose. The native level of TOS3 and SAK1 was essential for yeast cells to adapt glucose repression, but the overexpression of TOS3 and SAK1 alone repressed the expression of MALx1 in maltose-glucose and MALx2 in maltose. Moreover, the three kinases might regulate the maltose metabolism via the Snf1-parallel pathways with a carbon source-dependent manner. These results, for the first time, suggested that Elm1, rather than Tos3 and Sak1, might be the dominant regulator in the maltose metabolism of baker’s yeast. These findings provided knowledge about the glucose repression of maltose and gave a new perspective for breeding industrial yeasts with rapid maltose metabolism.

Highlights

Glucose repression is a key regulatory system controlling the synthesis of a series of enzymes involved in the carbohydrate metabolism in yeast (Trumbly, 1992; Klein et al, 1998; Carlson, 1999; Kim et al, 2019)
Saccharomyces cerevisiae Elm1, Tos3, and Sak1 kinases are known as the upstream regulators of the Snf1-Mig1 pathway in glucose repression (Hedbacker and Carlson, 2008)
The results suggested that Elm1, Tos3, and Sak1 played different roles in the regulation of the maltose metabolism of baker’s yeast

Summary

Introduction

Glucose repression is a key regulatory system controlling the synthesis of a series of enzymes involved in the carbohydrate metabolism in yeast (Trumbly, 1992; Klein et al, 1998; Carlson, 1999; Kim et al, 2019). In the presence of glucose, the expression of genes involved in the metabolism of alternate fermentable carbon sources (such as maltose, galactose, and sucrose), non-fermentable ones (such as glycerol, ethanol, and acetate), and respiratory metabolism is repressed (Srąan et al, 2004; Martinez-Ortiz et al, 2019; Lin, 2021). This disadvantage could be substantial in biotechnological production processes, in which glucose is sometimes not the primary carbon source or respiratory metabolism is demanded (Verstrepen et al, 2004). Alleviating glucose repression is essential to improve the utilization efficiency of non-glucose carbon sources

Methods

Results

Conclusion