Regulation of the thermoalkaliphilic F1-ATPase from Caldalkalibacillus thermarum.
The crystal structure has been determined of the F1-catalytic domain of the F-ATPase from Caldalkalibacillus thermarum, which hydrolyzes adenosine triphosphate (ATP) poorly. It is very similar to those of active mitochondrial and bacterial F1-ATPases. In the F-ATPase from Geobacillus stearothermophilus, conformational changes in the ε-subunit are influenced by intracellular ATP concentration and membrane potential. When ATP is plentiful, the ε-subunit assumes a "down" state, with an ATP molecule bound to its two C-terminal α-helices; when ATP is scarce, the α-helices are proposed to inhibit ATP hydrolysis by assuming an "up" state, where the α-helices, devoid of ATP, enter the α3β3-catalytic region. However, in the Escherichia coli enzyme, there is no evidence that such ATP binding to the ε-subunit is mechanistically important for modulating the enzyme's hydrolytic activity. In the structure of the F1-ATPase from C. thermarum, ATP and a magnesium ion are bound to the α-helices in the down state. In a form with a mutated ε-subunit unable to bind ATP, the enzyme remains inactive and the ε-subunit is down. Therefore, neither the γ-subunit nor the regulatory ATP bound to the ε-subunit is involved in the inhibitory mechanism of this particular enzyme. The structure of the α3β3-catalytic domain is likewise closely similar to those of active F1-ATPases. However, although the βE-catalytic site is in the usual "open" conformation, it is occupied by the unique combination of an ADP molecule with no magnesium ion and a phosphate ion. These bound hydrolytic products are likely to be the basis of inhibition of ATP hydrolysis.
Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Cambridge CB2 0XY, United Kingdom;
Scott A
SA
Ferguson
Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Cambridge CB2 0XY, United Kingdom; Department of Microbiology and Immunology, University of Otago, Dunedin 9016, New Zealand;
Gregory M
GM
Cook
Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Cambridge CB2 0XY, United Kingdom;
Martin G
MG
Montgomery
Medical Research Council Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge CB2 0QH, United Kingdom.
Andrew G W
AG
Leslie
Medical Research Council Mitochondrial Biology Unit, Cambridge Biomedical Campus, Cambridge CB2 0XY, United Kingdom; walker@mrc-mbu.cam.ac.uk.
John E
0000-0001-7929-2162
JE
Walker
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000468:Alkalies / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001407:Bacillus / Q000201:enzymology*; D055162:Biocatalysis; D002417:Cattle; D018360:Crystallography, X-Ray; D008928:Mitochondria / Q000378:metabolism; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D016415:Sequence Alignment; D055672:Static Electricity; D040681:Structural Homology, Protein; D013696:Temperature
D000468:Alkalies; D050505:Mutant Proteins; D021122:Protein Subunits; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases
Caldalkalibacillus thermarum; F1-ATPase; inhibition; regulation; structure