In October 25th, 2012, a paper entitled ‘Structural insight into the type-II mitochondrial NADH dehydrogenases’ was published on NATURE by Maojun Yang’s research group of Tsinghua University. In this research , the crystal structure of NADH:ubiquinone oxidoreductase Ndi1 was firstly reported, and its physiological function and mechanism were also thoroughly investigated. This work was accomplished with the help of EPR (Electron paramagnetic resonance) under the cooperation and support of the research fellows from CHMFL.

EPR can effectively reveal the spin state and dynamics of electrons. There are a number of radicals containing unpaired electrons in beings. The electron transfer between macromolecules plays vital roles in energy generation, metabolism and so on. EPR is an important Research technique in revealing the radicals states and interconversion process in the electron transfer between the membrane proteins of the cellular respiratory chain.

Maojun Yang’s group of Tsinghua University successfully solved the crystal structures of Ndi1 and its complexes with NADH, UQ, and NADH-UQ. It was confirmed that there were two ubiquinone binding sites in Ndi1 by the research fellows from CHMFL using EPR. The existence of ubisemiquinone radicals was detected by EPR during the Ndi1 catalyzed electron transfer process from NADH to UQ. The signal intensity of ubisemiquinone radicals increased along with the increase of the concentration of UQ. Moreover, the power saturation experiments suggested the existence of two different populations of ubisemiquinone radicals. Based on the results of EPR experiments, the authors came up with a model in which Ndi1 catalyses the electron transfer from NADH to UQII through a mechanism mediated by the FAD–UQI intermediate.

Related link: http://www.nature.com/nature/journal/v491/n7424/full/nature11541.html 

Figure 1: Ndi1 has a unique CTD

Figure 2: The CTD mediates Ndi1 homodimerization and membrane attachment

Figure 3: Electron transfer of Ndi1 involves two ubiquinone molecules