Microbiology and Wine Research, Institute of Molecular Physiology (IMP), Johannes Gutenberg-University Mainz, Mainz, 55099, Germany.
Mol Microbiol. 2018 Sep;109(6):801-811. doi: 10.1111/mmi.14074. Epub 2018 Jul 30.
DcuA of Escherichia coli is known as an alternative C -dicarboxylate transporter for the main anaerobic C -dicarboxylate transporter DcuB. Since dcuA is expressed constitutively under aerobic and anaerobic conditions, DcuA was suggested to serve aerobically as a backup for the aerobic (DctA) transporter, or for the anabolic uptake of C -dicarboxylates. In this work, it is shown that DcuA is required for aerobic growth with L-aspartate as a nitrogen source, whereas for growth with L-aspartate as a carbon source, DctA was needed. Strains with DcuA catalyzed L-aspartate and C -dicarboxylate uptake (like DctA), or an L-aspartate/C -dicarboxylate antiport (unlike DctA). DcuA preferred L-aspartate to succinate in transport (K = 43 and 844 µM, respectively), whereas DctA has higher affinity for C -dicarboxylates like succinate compared to L-aspartate. When L-aspartate was supplied as the sole nitrogen source together with glycerol as the carbon source, L-aspartate was taken up by the bacteria and fumarate (or L-malate) was excreted in equimolar amounts. Both reactions depended on DcuA. L-Aspartate was taken up in amounts required for nitrogen metabolism but not for carbon metabolism. Therefore, DcuA catalyzes an L-aspartate/C -dicarboxylate antiport serving as a nitrogen shuttle for nitrogen supply without net carbon supply.
大肠杆菌的 DcuA 是一种替代的主要厌氧 C-二羧酸转运蛋白 DcuB 的 C-二羧酸转运蛋白。由于 dcuA 在需氧和厌氧条件下持续表达，因此推测 DcuA 在需氧条件下作为有氧（DctA）转运蛋白的备用，或用于 C-二羧酸的合成摄取。在这项工作中，结果表明 DcuA 是有氧生长所需的，以 L-天冬氨酸作为氮源，而以 L-天冬氨酸作为碳源的生长则需要 DctA。具有 DcuA 催化 L-天冬氨酸和 C-二羧酸摄取（如 DctA），或 L-天冬氨酸/C-二羧酸反向转运（与 DctA 不同）的菌株。DcuA 在转运中优先选择 L-天冬氨酸而不是琥珀酸（K = 43 和 844 µM），而 DctA 对琥珀酸等 C-二羧酸的亲和力比对 L-天冬氨酸更高。当 L-天冬氨酸作为唯一氮源与甘油作为碳源一起供应时，细菌会摄取 L-天冬氨酸并以等摩尔量排出富马酸（或 L-苹果酸）。这两个反应都依赖于 DcuA。L-天冬氨酸的摄取量足以满足氮代谢的需要，但不足以满足碳代谢的需要。因此，DcuA 催化 L-天冬氨酸/C-二羧酸反向转运，作为氮源的氮穿梭，而不提供净碳源。
