Lactobacillus reuteri synthesizes γ-glutamyl dipeptides in sourdough

γ-Glutamyl Cysteine Ligase of Lactobacillus reuteri Synthesizes γ-Glutamyl Dipeptides in Sourdough

Journal & Pages: Journal of Agricultural and Food Chemistry, 2018, 66(46): 12368-12375.

Abstract: Kokumi active γ-glutamyl dipeptides (γ-GPs) accumulate in fermented food. γ-Glutamyl transferase, glutaminase, glutathione synthetase and γ-glutamyl cysteine ligase (GCL) may synthesize γ-GPs. The genome of Lactobacillus reuteri encodes GCL but not glutathione synthetase or glutamyl transferase, therefore, this study investigated the role of GCL in γ-GPs synthesis by L. reuteri LTH5448. Phylogenomic analysis of gcl in lactobacilli demonstrated three genes coding for GCL are present in L. reuteri; two of these are present in L. reuteri LTH5448. Two deletion mutants of L. reuteri LTH5448, L. reuteri LTH5448Δgcl1 and LTH5448Δgcl1Δgcl2 were constructed by double crossover mutagenesis. Growth and oxygen resistance of the mutants were comparable with to the wild type. γ-Glu-Glu, γ-Glu-Leu, γ-Glu-Ile, γ-Glu-Val and γ-Glu-Cys were quantified in buffer and sourdough fermentations by LC-MS. Wild-type and L. reuteri Δgcl1 but not Δgcl1Δgcl2 converted amino acids to γ-Glu-Cys. γ-Glu-Ile accumulation was reduced in both mutants, however, the disruption of gcl did not alter the biosynthesis of the other γ-GPs. In conclusion, gcl1 in L. reuteri mediates γ-Glu-Ile synthesis, gcl2 mediates γ-Glu-Cys synthesis but neither gene affected synthesis of other γ-GPs. This study facilitates selection of starter cultures that synthesize γ-Glu-peptides with kokumi activity and thus improve the taste of fermented foods.

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【作者提要】

γ-谷氨酰二肽作为馒头特征滋味物质，对馒头的整体滋味特性有着重要的作用。我们的研究主要通过构建罗伊氏乳杆菌LTH5448突变菌株，阐明了乳酸菌中γ-谷氨酰二肽代谢形成机制。结果表明大多数谷氨酰半胱氨酸连接酶存在于异型发酵乳杆菌中，仅有少部分存在于同型发酵乳杆菌中，而罗伊氏乳杆菌LTH5448中主要含有两个氨酰半胱氨酸连接酶编码基因gcl1和gcl2。其中基因gcl1优先选择异亮氨酸用于调控γ-谷氨酰异亮氨酸的合成，而基因gcl2则优先选择半胱氨酸用于调控γ-谷氨酰半胱氨酸的合成，这为乳酸菌发酵高产γ-谷氨酰二肽并提高发酵食品的滋味奠定了理论基础。

Authors:

Bowen Yan^1,2, Yuan Yao Chen¹, Weilan Wang¹, Jianxin Zhao², Wei Chen², Michael Gänzle^1,2,3*

1. University of Alberta, Department of Agricultural, Food and Nutritional Science, Edmonton, AB, Canada;

2. School of Food Science and Technology, Jiangnan University, Wuxi, P.R. China;

3. Hubei University of Technology, College of Bioengineering and Food Science, Wuhan, P.R. China

Link: 10.1021/acs.jafc.8b05056