JOSHI, Saroj
Senior Scientist, Boston Biomedical Research Institute
Research Associate, Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School
B.Sc., Delhi University, Biology, 1956
Ph.D., North Carolina State University, Biochemistry, 1971
RESEARCH INTERESTS
Oxidative phosphorylation. Energy coupling mechanisms in mitochondrial proton pumping ATPase.
SUMMARY OF RESEARCH
The synthesis of ATP in mitochondria occurs in two steps. The first step in the formation of ATP is a movement of protons, driven out by the energy of oxidation from inside the mitochondrion. The second step, driven by the reversed flow of protons, is the actual synthesis of ATP. This process is catalyzed by an enzyme complex named ATP synthase, consisting of a catalytic segment F1, a proton-translocating segment Fo, and an intervening segment, stalk, that brings about the coupling of F1 and Fo segments. In order to have a better understanding of the communication between Fo and F1 we have to know more about a protein - the oligomycin sensitivity conferring protein (OSCP) - located at their interface, which plays a key role in the transfer of energy between the two segments. As its name implies, OSCP renders the F1 enzyme sensitive to the antibiotic oligomycin, which results in the inhibition of the activity of F1. We have cloned the OSCP gene in bacteria and are using genetic engineering approaches in which various regions suspected of interacting with F1 are modified to obtain mutant forms. We shall study the effect of these mutations on the ability of OSCP to couple the flow of protons to ATP synthesis. Recent X-ray diffraction studies in the U.K. have established the structure of the F1 component of the ATPase on the atomic level. This work will help to design genetically engineered mutants aimed at identification of the key sites in the interaction between the F1 and Fo components of this important enzyme. It is hoped that this kind of analysis will lead to a better understanding of the mechanism of ATP synthesis in normal and diseased tissue, which may eventually help in diagnosing and possibly curing neurodegenerative diseases that involve defects in mitochondria.
SELECTED PUBLICATIONS
Joshi, S., Cao, G.-J., Noth, C., & J. Shah (1996) Oligomycin sensitivity-conferring protein of mitochondrial ATP synthesis: Deletions in the N-terminal end cause difects in interactions with F1, while deletions in the C-terminal end cause difects in interactions with Fo. Biochemistry 35, 12094-12103.
Joshi, S., Javed, A.A. & Gibbs, L.C. (1992) Oligomycin Sensitivity-conferring Protein (OSCP) of Mitochondrial ATP Synthase - The Carboxyl-terminal Region of OSCP is Essential for the Reconstitution of Oligomycin-sensitive H+-ATPase. J. Biol. Chem. 267, 12860-12867.
Joshi, S. & Burrows, R. (1990) ATP Synthase Complex from Bovine Heart Mitochondria - Subunit Arrangement as Revealed by Nearest Neighbor Analysis and Susceptibility to Trypsin. J. Biol. Chem. 265, 14518-14525.
Pringle, M.J., Kenneally, M.K. & Joshi, S. (1990) ATP Synthase Complex from Bovine Mitochondria - Passive H+ Conduction Through F0 Does Not Require Oligomycin Sensitivity-Conferring Protein. J. Biol. Chem. 265, 7632-7637.
Joshi, S. & Burrows, R. (1990) Subunit Arrangement in Bovine Mitochondrial H+-ATPase. In: Structure, Function and Assembly of ATP Synthetase, ed. S. Marzuki, Plenum Publishing Corp, p. 171.
Joshi, S. & Pringle, M.J. (1989) ATP-Synthase Complex from Bovine Heart Mitochondria: Passive H+-Conduction through Mitochondrial Coupling Factor 6-Depleted Fo Complexes. J. Biol. Chem. 264, 15548-15551.
Joshi, S., Pringle, M.J. & Siber, R. (1986) Topology and Function of "Stalk" Proteins in the Bovine Mitochondrial H+-ATPase. J. Biol. Chem. 261, 10653-10658.
Sanadi, D.R., Joshi, S., Huang, Y., Kantham, L., Pringle, M.J. & Hughes, J.B. (1985) On the Role of FB Dithiol and Other Dithiols in H+ Conductance in Mitochondrial Fo. In: Achievements and Perspectives of Mitochondrial Research, Bioenergetics, Vol. I (E. Quagliariello, E.C. Slater, C. Saccone and A.M. Kroon, eds.) Elsevier/The Netherlands, pp. 269.
Torok, K. & Joshi, S. (1985) Cross-linking of Bovine Mitochondrial H+-ATPase by Copper-o-Phenanthroline. Interaction of the Oligomycin-Sensitivity-Conferring Protein with a 24-kDa protein. Eur. J. Biochem. 153, 155-159.
Torok, K. & Joshi, S. (1985) Formation of an Intramolecular Disulfide Bond in the Mitochondrial Adenine Nucleotide Translocase. FEBS Letts. 182, 340-344.
Joshi, S. Hughes J.B., Torok, K. & Sanadi, D.R. (1985) Resolution and reconstitution of H+ -ATPase complex from beef heart mitochondria. J. Membrane Biochem. 5, 309-25.