Functional Identification of Novel Genes Involved in the Glutathione-Independent Gentisate Pathway inCorynebacterium glutamicum

Abstract
Corynebacterium glutamicumused gentisate and 3-hydroxybenzoate as its sole carbon and energy source for growth. By genome-wide data mining, a gene cluster designatedncg12918-ncg12923was proposed to encode putative proteins involved in gentisate/3-hydroxybenzoate pathway. Genes encoding gentisate 1,2-dioxygenase (ncg12920) and fumarylpyruvate hydrolase (ncg12919) were identified by cloning and expression of each gene inEscherichia coli. The gene ofncg12918encoding a hypothetical protein (Ncg12918) was proved to be essential for gentisate-3-hydroxybenzoate assimilation. Mutant strain RES167Δncg12918lost the ability to grow on gentisate or 3-hydroxybenzoate, but this ability could be restored inC. glutamicumupon the complementation with pXMJ19-ncg12918. Cloning and expression of thisncg12918gene inE. colishowed that Ncg12918 is a glutathione-independent maleylpyruvate isomerase. Upstream ofncg12920, the genesncg12921-ncg12923were located, which were essential for gentisate and/or 3-hydroxybenzoate catabolism. The Ncg12921 was able to up-regulate gentisate 1,2-dioxygenase, maleylpyruvate isomerase, and fumarylpyruvate hydrolase activities. The genesncg12922andncg12923were deduced to encode a gentisate transporter protein and a 3-hydroxybenzoate hydroxylase, respectively, and were essential for gentisate or 3-hydroxybenzoate assimilation. Based on the results obtained in this study, a GSH-independent gentisate pathway was proposed, and genes involved in this pathway were identified.

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