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Complex I (NADH:ubiquinone oxidoreductase)

Complex I – the entry point of electrons into the respiratory chain of all higher organisms – is the last of the respiratory enzymes whose mechanism remains unknown. In mitochondria, complex I oxidises NADH from sugars and fats, reduces ubiquinone and transports protons across the inner mitochondrial membrane, thereby contributing to the proton motive force that enables ATP-synthase to make ATP.

In collaboration with the Hirst group in Cambridge, we are working on elucidating some of the key elements of the mechanism of complex I using advanced EPR methods, in particular we are fascinated how the redox energy built up through electron transfer is used to drive proton translocation. Given the large size of the enzyme (the size of the mitochondrial enzyme is ca. 1 MDa), many biophysical methods routinely applied to study protein cannot be used (e.g. NMR). We are exploiting the fact that EPR spectroscopy is blind to all the many paired electrons in the complex, and that unpaired electrons are situated in mechanistically key locations. For instance, many of the iron-sulfer clusters ([2Fe-2S] and [4Fe-4S] clusters) become EPR-visible when reduced. We have recently divised a potentiometric method that enables us to adjust very small amounts of protein to very precise reduction potentials - an important prerequisite for studying these redox-active proteins spectroscopically. We are also using site-directed mutagenesis to alter residues in the enzyme, and thus to probe their mechanistic relevance.


Project members and collaborators:
Dr John Wright (PDRA, QMUL)
Kaltum Abdiaziz (PhD student, QMUL)
Dr Judy Hirst (PI, Medical Research Council, Mitochondrial Biology Unit, Cambridge)

The NAD(P)H dehydrogenase 'like' complex (NDH)

We have teamed up with Dr Guy Hanke to investigate the fascinating molecular machine NDH, in many ways related to the mitochondrial enzyme (complex I, above), present in plants and cyanobacteria. Our goal is to unravel the mechanism of NDH, and ultimately to exploit this knowledge in order to increase stress tolerance in plants (in collaboration with Prof. Nestor Carrillo, Rosario, Argentina). Increasing crop yields is an especially important challenge facing the developing world, but may affect us all one day given the ever rising world population. Research on NDH has thus far focused on genetic investigations and very little is know about the function of NDH, and no biophysical studies are reported. Using our experience with the mitochondrial enzyme, we are using EPR spectroscopy and protein film electrochemistry to investigate the co-factors in and the electron donors to NDH. Moreover, the knowledge gained through NDH is also likely relevant for understanding the mechanism of complex I.

See Dr Hanke's webpage for more details on the biological context.

Project members and collaborators:
Gemma McGuire (PhD student, QMUL)
Katherina Richardson (PhD student, QMUL LIDo program)
Dr Guy Hanke (PI, School of Biological and chemical Sciences, QMUL)

Interlocked transition-metal complexes

In recent years, much research has been devoted to the construction of mechanically interlocked molecules (for an example see below). Notably, the pioneering work of Sauvage, Stoddart and Feringa was recently recognised with the 2016 Nobel Prize in Chemistry. The unusual structure of these molecules leads to unusual properties (see, for example this recent review paper by our collaborators), that are increasingly being exploited for functional applications that may lead to the development of sensors, new materials and energy storage systems. With the help of our synthetic wizards at the University of Southampton (Goldup group) we are investigating the properties (e.g. redox potentials, spin state changes, and catalysis) of 'trapped' transition metals through EPR spectroscopy and electrochemistry,


Project members and collaborators:
Martina Cirulli (PhD student, QMUL Materials Reserach Institute)
Dr Steve Goldup (PI, Department of Chemistry, University of Southampton)