Bott Michael, Niebisch Axel
Institut für Biotechnologie 1, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany.
J Biotechnol. 2003 Sep 4;104(1-3):129-53. doi: 10.1016/s0168-1656(03)00144-5.
Corynebacterium glutamicum is an aerobic bacterium that requires oxygen as exogenous electron acceptor for respiration. Recent molecular and biochemical analyses together with information obtained from the genome sequence showed that C. glutamicum possesses a branched electron transport chain to oxygen with some remarkable features. Reducing equivalents obtained by the oxidation of various substrates are transferred to menaquinone via at least eight different dehydrogenases, i.e. NADH dehydrogenase, succinate dehydrogenase, malate:quinone oxidoreductase, pyruvate:quinone oxidoreductase, D-lactate dehydrogenase, L-lactate dehydrogenase, glycerol-3-phosphate dehydrogenase and L-proline dehydrogenase. All these enzymes contain a flavin cofactor and, except succinate dehydrogenase, are single subunit peripheral membrane proteins located inside the cell. From menaquinol, the electrons are passed either via the cytochrome bc(1) complex to the aa(3)-type cytochrome c oxidase with low oxygen affinity, or to the cytochrome bd-type menaquinol oxidase with high oxygen affinity. The former branch is exceptional, in that it does not involve a separate cytochrome c for electron transfer from cytochrome c(1) to the Cu(A) center in subunit II of cytochrome aa(3). Rather, cytochrome c(1) contains two covalently bound heme groups, one of which presumably takes over the function of a separate cytochrome c. The bc(1) complex and cytochrome aa(3) oxidase form a supercomplex in C. glutamicum. The phenotype of defined mutants revealed that the bc(1)-aa(3) branch, but not the bd branch, is of major importance for aerobic growth in minimal medium. Changes of the efficiency of oxidative phosphorylation caused by qualitative changes of the respiratory chain or by a defective F(1)F(0)-ATP synthase were found to have strong effects on metabolism and amino acid production. Therefore, the system of oxidative phosphorylation represents an attractive target for improving amino acid productivity of C. glutamicum by metabolic engineering.
谷氨酸棒杆菌是一种需氧细菌，呼吸时需要氧气作为外源电子受体。最近的分子和生化分析以及从基因组序列中获得的信息表明，谷氨酸棒杆菌拥有一条通向氧气的分支电子传递链，具有一些显著特征。通过各种底物氧化获得的还原当量通过至少八种不同的脱氢酶转移至甲萘醌，即NADH脱氢酶、琥珀酸脱氢酶、苹果酸：醌氧化还原酶、丙酮酸：醌氧化还原酶、D-乳酸脱氢酶、L-乳酸脱氢酶、甘油-3-磷酸脱氢酶和L-脯氨酸脱氢酶。所有这些酶都含有黄素辅因子，除琥珀酸脱氢酶外，均为位于细胞内的单亚基外周膜蛋白。从甲萘氢醌开始，电子要么通过细胞色素bc(1)复合体传递给低氧亲和力的aa(3)型细胞色素c氧化酶，要么传递给高氧亲和力的细胞色素bd型甲萘氢醌氧化酶。前一个分支很特别，因为它在从细胞色素c(1)到细胞色素aa(3)亚基II中的Cu(A)中心的电子传递过程中不涉及单独的细胞色素c。相反，细胞色素c(1)含有两个共价结合的血红素基团，其中一个可能承担单独细胞色素c的功能。在谷氨酸棒杆菌中，bc(1)复合体和细胞色素aa(3)氧化酶形成一个超复合体。特定突变体的表型表明，bc(1)-aa(3)分支而非bd分支对于在基本培养基中的有氧生长至关重要。发现呼吸链的定性变化或有缺陷的F(1)F(0)-ATP合酶导致的氧化磷酸化效率变化对代谢和氨基酸生产有强烈影响。因此，氧化磷酸化系统是通过代谢工程提高谷氨酸棒杆菌氨基酸生产力的一个有吸引力的靶点。
