Tetsu Shimizu1, Naoki Takaya, Akira Nakamura. 1. Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
Abstract
BACKGROUND: L-Glucose, the enantiomer of D-glucose, was believed not to be utilized by any organisms. RESULTS: An L-glucose-utilizing bacterium was isolated, and its L-glucose catabolic pathway was identified genetically and enzymatically. CONCLUSION: L-Glucose was utilized via a novel pathway to pyruvate and D-glyceraldehyde 3-phosphate. SIGNIFICANCE: This might lead to an understanding of homochirality in sugar metabolism. An L-glucose-utilizing bacterium, Paracoccus sp. 43P, was isolated from soil by enrichment cultivation in a minimal medium containing L-glucose as the sole carbon source. In cell-free extracts from this bacterium, NAD(+)-dependent L-glucose dehydrogenase was detected as having sole activity toward L-glucose. This enzyme, LgdA, was purified, and the lgdA gene was found to be located in a cluster of putative inositol catabolic genes. LgdA showed similar dehydrogenase activity toward scyllo- and myo-inositols. L-Gluconate dehydrogenase activity was also detected in cell-free extracts, which represents the reaction product of LgdA activity toward L-glucose. Enzyme purification and gene cloning revealed that the corresponding gene resides in a nine-gene cluster, the lgn cluster, which may participate in aldonate incorporation and assimilation. Kinetic and reaction product analysis of each gene product in the cluster indicated that they sequentially metabolize L-gluconate to glycolytic intermediates, D-glyceraldehyde-3-phosphate, and pyruvate through reactions of C-5 epimerization by dehydrogenase/reductase, dehydration, phosphorylation, and aldolase reaction, using a pathway similar to L-galactonate catabolism in Escherichia coli. Gene disruption studies indicated that the identified genes are responsible for L-glucose catabolism.
BACKGROUND:L-Glucose, the enantiomer of D-glucose, was believed not to be utilized by any organisms. RESULTS: An L-glucose-utilizing bacterium was isolated, and its L-glucose catabolic pathway was identified genetically and enzymatically. CONCLUSION:L-Glucose was utilized via a novel pathway to pyruvate and D-glyceraldehyde 3-phosphate. SIGNIFICANCE: This might lead to an understanding of homochirality in sugar metabolism. An L-glucose-utilizing bacterium, Paracoccus sp. 43P, was isolated from soil by enrichment cultivation in a minimal medium containing L-glucose as the sole carbon source. In cell-free extracts from this bacterium, NAD(+)-dependent L-glucose dehydrogenase was detected as having sole activity toward L-glucose. This enzyme, LgdA, was purified, and the lgdA gene was found to be located in a cluster of putative inositol catabolic genes. LgdA showed similar dehydrogenase activity toward scyllo- and myo-inositols. L-Gluconate dehydrogenase activity was also detected in cell-free extracts, which represents the reaction product of LgdA activity toward L-glucose. Enzyme purification and gene cloning revealed that the corresponding gene resides in a nine-gene cluster, the lgn cluster, which may participate in aldonate incorporation and assimilation. Kinetic and reaction product analysis of each gene product in the cluster indicated that they sequentially metabolize L-gluconate to glycolytic intermediates, D-glyceraldehyde-3-phosphate, and pyruvate through reactions of C-5 epimerization by dehydrogenase/reductase, dehydration, phosphorylation, and aldolase reaction, using a pathway similar to L-galactonate catabolism in Escherichia coli. Gene disruption studies indicated that the identified genes are responsible for L-glucose catabolism.
Authors: Merlin Eric Hobbs; Howard J Williams; Brandan Hillerich; Steven C Almo; Frank M Raushel Journal: Biochemistry Date: 2014-07-07 Impact factor: 3.162