PARENT SESSION

Symposium S1A Proton-coupled electon transport and ATPase
Monday August 30th, 2004 10:20 AM-12:20 PM Room 511D
Chair: Colin Wraight
Co-Chair: Wolfgang Junge

Chloroplast F₁-ATPase: Molecular mechanism of the phytotoxin tentoxin. Nicole Koertgen¹, Claudia Schnick¹, Dirk Bald³, Holger Lill³, Toru Hisabori⁵, Georg Groth^*,1, ¹ University of Duesseldorf, Duesseldorf, Germany³ Department of Structural Biology, Amsterdam, Netherlands⁵ Chemical Resources Laboratory, Yokohama, Japan

ABSTRACT- The chloroplast F₁F₀-ATP synthase, a complex multi-subunit enzyme of 550 kDa, catalyses ATP synthesis and ATP hydrolysis coupled to proton translocation across the thylakoid membrane. The catalytic activity of the chloroplast ATPase in certain sensitive species of plants is modulated by the natural cyclic tetrapeptide tentoxin which causes inhibition at low and activation at high concentrations. Bacterial or mitochondrial ATPases, on the other hand, are not affected by this toxin. The crystal structure of the tentoxin inhibited CF₁-complex [1, 2] revealed the binding site and the potential molecular mechanism of the inhibitor. The structure suggests that the inhibitor is hydrogen bonded to Asp-83 in the catalytic beta-subunit but forms hydrophobic contacts with several residues in the adjacent alpha-subunit. Tentoxin seems to act by inhibiting inter-subunit contacts at the alpha-beta-interface and by blocking the inter-conversion of binding sites in the catalytic mechanism [1]. Based on the structural information obtained from the CF₁-tentoxin complex sensitivity to the plant specific inhibitor was introduced to typically resistant enzymes from E. coli and Bacillus PS3 by site directed mutagenesis [3, 4]. Rotation studies on single molecules of the engineered tentoxin-sensitive F₁-ATPase from the thermophilic Bacillus PS3 indicate that inhibition by low concentrations of tentoxin caused a virtually complete stop of the gamma-subunit rotation. Re-activation at high concentrations of tentoxin restores rotational movement but with altered characteristics as compared with the non-inhibited enzyme [5]. References [1] Groth, G. (2002) Proc. Natl. Acad. Sci. USA 99, 3464 [2] Groth, G. (2003) Recent Res. Devel. Biochem. 4, 903 [3] Groth, G., Hisabori, T., Lill, H. & Bald, D. (2002) J. Biol. Chem. 277, 20117. [4] Schnick, C., Koertgen, N. & Groth, G. (2002) J. Biol. Chem. 277, 51003. [5] Pavlova, P., Shimabukuro, K., Hisabori, T., Groth, G., Lill, H. & Bald, D. (2004) J. Biol. Chem. 279, 9685.

KEY WORDS: tentoxin, molecular mechanism, ATP synthase, crystal structure