Cardiovascular Research

Dr Alexander Galkin

Effect of conformational changes of Complex I on mitochondrial hypoxic response, nitrosation of the enzyme and postischaemic injury

Mitochondrial complex I is located at an entry point of the electron transport chain and catalyses electron transfer from NADH obtained in the Krebs cycle to ubiquinone (coenzyme Q). Despite the importance of complex I for cellular metabolism, little is known about its regulation in vivo.

Complex I is known to undergo reversible conformational changes in situations in which its turnover is limited. This unusual behaviour of the enzyme is known as “active/de-active” transition and has been observed in various membrane preparations of the enzyme: mitochondria, submitochondrial particles or isolated Complex I (for review see Vinogradov & Grivennikova, 2001). In the absence of substrates and at physiological temperatures (>30ºC) the mammalian enzyme is rapidly converted into the de-active, dormant form. This form is catalytically incompetent but can be activated by the slow reaction (k~4 min-1) of NADH oxidation with subsequent ubiquinone reduction. After one or several turnovers the enzyme becomes active and can catalyse physiological NADH:ubiquinone reactions at a much higher rate (k~104 min-1).

Recently we found that these conformational changes may have physiological significance. The de-active, but not the active form of Complex I is susceptible to inhibition by nitrosothiols and peroxynitrite, which most likely occurs at cysteine-39 of subunit ND3 (Fig 1) [Galkin et al, 2008; Galkin & Moncada, 2007]. It is likely that transition from the active to the de-active form of complex I takes place during pathological conditions when the turnover of the enzyme is limited at physiological temperatures, such as during hypoxia, or when the tissue nitric oxide:oxygen ratio increases (i.e. metabolic hypoxia [Moncada & Erusalimsky, 2002; Galkin et al., 2007]). In such a situation the spontaneous de-activation of complex I would result in increasing sensitivity to nitrosating agents (S-nitrosoglutathione or peroxynitrite) followed by blocking of the enzyme in the de-active state (Fig 2).

We propose that hypoxic A/D transition, which is initially protective, may become an early step in the initiation of pathophysiology during prolonged hypoxia or inflammation as a result of the modification of Complex I via NO-dependent pathways, which impedes its return to the A-form (Fig. 2).

Selected publications

Galkin A, Meyer B, Wittig I, Karas M, Schägger H, Vinogradov A, Brandt U. (2008). Identification of the mitochondrial ND3 subunit as a structural component involved in the active/deactive enzyme transition of respiratory complex I. J.Biol.Chem. 283, 20907-20913. PMID: 18502755

Galkin A., Moncada S. (2007). S-nitrosation of mitochondrial complex I depends on its structural conformation. J.Biol.Chem. 282, 37448-37453. PMID: 17956863

Galkin A., Higgs A., Moncada S. (2007). Nitric oxide and hypoxia. Essays Biochem. 43, 29-42. PMID: 17705791

Moncada S., Erusalimsky J.D. (2002). Does nitric oxide modulate mitochondrial energy generation and apoptosis? Nat.Rev.Mol.Cell.Biol. 3, 214-220. PMID: 11994742

Vinogradov, A.D., Grivennikova, V.G. (2001) The mitochondrial complex I: progress in understanding of catalytic properties. IUBMB Life, 52,129–134.

Academic Career

2006-present Senior Research Fellow, Wolfson Institute for Biomedical Research, UCL

2004 –2006 Postdoctoral Fellow, University of Frankfurt, Germany Laboratory of Molecular Bioenergetics

2001-2003 Postdoctoral Fellow in Biochemistry Department of Lund University, Lund, Sweden.

1996- 2001 Ph.D. Biochemistry Science, Department of Biochemistry School of Biology, Moscow State University, Russia

Funding

Figure 1: Effect of S-nitrosoglutathione on NADH-oxidase activity of the acitve (A) and deactive (D) form of Complex I

Figure 2: De-activation of Complex I in hypoxia results in exposure of cysteine-39 of the ND3 subunit which can be modified by S-nitroso-glutathione or peroxynitrite.

Links

Complex I homepage

Joel Weiner Complex II related webpage

The bc1 complex homepage

The Cytochrome Oxidase homepage

Boris Feniouk ATP synthase homepage

Antony Crofts bioenergetics course