[[File:Towheed MA.jpg|right|200px|Mohammad Atif Towheed]]
Mitochondrial missense mutations lead to devastating disorders in humans known as mitochondrial encephalomyopathies. Our lab has previously identified a pathogenic mutation (G116E) in Drosophila ATP6, which is a subunit of Complex V of the mitochondrial electron transport chain. This mutation causes progressive neuromuscular dysfunction and myodegeneration, and is a model for human mitochondrial disorders such as NARP (neuropathy, ataxia, and retinitis pigmentosa), MILS (maternally inherited Leigh's syndrome), and FBSN (familial bilateral striatal necrosis).
The underlying pathophysiology of these mutant flies is not clearly understood. In addition to shortened lifespan, myopathy and neural dysfunction, these flies also exhibit abnormal mitochondrial morphology in ~60% of its mitochondria. The mitochondrial cristae are dilated as opposed to flat cristae in wild-type flies. Complex V is unable to efficiently dimerize and ATP synthase activity is severely diminished in ATP6  flies . However, complex V ATPase activity is detectable and the membrane potential is not affected. These mutant flies also show an increase in ROS as a function of age. Earlier studies suggest that the complexes of the electron transport chain play a role in maintaining normal mitochondrial cristae morphology [2,3]. We hypothesize that this missense mutation affects Complex V dimerization as it lies at the dimer interface and contributes significantly to the pathogenesis. To test our hypothesis, we use RNAi to knock down subunits ATPe and ATPg that are known to assist in ATP synthase dimerization [4,5].
Since, mitochondrial disorders have a tissue specific pattern of presentation, we examine which tissue contributes to the pathophysiology most by using specific GAL4 fly lines. ATPe and/or ATPg are knocked down in either muscle or neuronal tissues and their motor function and life spans are tested. In addition, we are investigating the altered physiology of the mitochondria in these mutants. To determine how the ATP6  flies use their mitochondrial electron transport chain, we will investigate the mitochondrial oxidative phosphorylation using high-resolution respirometry. Respirometry and measures of biochemical activities of mitochondrial specific enzymes will help to elucidate the pathophysiology of mitochondrial diseases ''in vivo''.
 [http://www.ncbi.nlm.nih.gov/pubmed/16421301 Celotto AM, Frank AC, McGrath SW, Fergestad T, Van Voorhies WA, Buttle KF, Mannella CA, Palladino MJ (2006) Mitochondrial encephalomyopathy in Drosophila. J Neurosci 26: 810-820 Open Access]
 [http://www.ncbi.nlm.nih.gov/pubmed?term=Structure%20of%20dimeric%20ATP%20synthase%20from%20mitochondria%3A%20an%20angular%20association%20of%20monomers%20induces%20the%20strong%20curvature%20of%20the%20inner%20membrane Dudkina NV, Heinemeyer J, Keegstra W, Boekema EJ, Braun HP (2005) Structure of dimeric ATP synthase from mitochondria: an angular association of monomers induces the strong curvature of the inner membrane. FEBS Lett 579: 5769-5772]
 [http://www.ncbi.nlm.nih.gov/pubmed?term=Dimer%20ribbons%20of%20ATP%20synthase%20shape%20the%20inner%20mitochondrial%20membrane Strauss M, Hofhaus G, Schroeder RR, Kühlbrandt W (2008) Dimer ribbons of ATP synthase shape the inner mitochondrial membrane. EMBO J 27: 1154-1160 Open Access]embrane. EMBO J 27: 1154-1160 Open Access]