Coupling proton movement to ATP synthesis in the chloroplast ATP synthase.
The chloroplast F(0)F(1)-ATP synthase-ATPase is a tiny rotary motor responsible for coupling ATP synthesis and hydrolysis to the light-driven electrochemical proton gradient. Reversible oxidation/reduction of a dithiol, located within a special regulatory domain of the gamma subunit of the chloroplast F(1) enzyme, switches the enzyme between an inactive and an active state. This regulatory mechanism is unique to the ATP synthases of higher plants and its physiological significance lies in preventing nonproductive depletion of essential ATP pools in the dark. The three-dimensional structure of the chloroplast F(1) gamma subunit has not yet been solved. To examine the mechanism of dithiol regulation, a model of the chloroplast gamma subunit was obtained through segmental homology modeling based on the known structures of the mitochondrial and bacterial gamma subunits, together with de novo construction of the unknown regulatory domain. The model has provided considerable insight into how the dithiol might modulate catalytic function. This has, in turn, suggested a mechanism by which rotation of subunits in F(0), the transmembrane proton channel portion of the enzyme, can be coupled, via the epsilon subunit, to rotation of the gamma subunit of F(1) to achieve the 120 degrees (or 90 degrees +30 degrees) stepping action that is characteristic of F(1) gamma subunit rotation.
Richter
Mark L
ML
Departments of Chemistry and Molecular Biosciences, The University of Kansas, Lawrence, Kansas 66045, USA. richter@ku.edu
Samra
Hardeep S
HS
He
Feng
F
Giessel
Andrew J
AJ
Kuczera
Krzysztof K
KK
D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D025222:Chloroplast Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000378:metabolism; D021122:Protein Subunits; D011522:Protons; D014050:Toluene / Q000031:analogs & derivatives
D020409:Molecular Motor Proteins; D021122:Protein Subunits; D011522:Protons; D014050:Toluene; D000255:Adenosine Triphosphate; D025222:Chloroplast Proton-Translocating ATPases; C004848:dithiol