Regulation of the thermoalkaliphilic F₁-ATPase from Caldalkalibacillus thermarum

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 113; no. 39; pp. 10860 - 10865
• Main Authors: Ferguson, Scott A., Cook, Gregory M., Montgomery, Martin G., Leslie, Andrew G. W., Walker, John E.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 27.09.2016
• Subjects: Adenosine Diphosphate - metabolism; Adenosine triphosphatase; Adenosine Triphosphate - metabolism; Alkalies - metabolism; Amino Acid Sequence; Animals; Bacillus - enzymology; Binding sites; Biocatalysis; Biochemistry; Biological Sciences; Cattle; Crystal structure; Crystallography, X-Ray; E coli; Enzymes; Gram-positive bacteria; Mitochondria - metabolism; Models, Molecular; Mutant Proteins - chemistry; Mutant Proteins - isolation & purification; Mutant Proteins - metabolism; Protein Subunits - chemistry; Protein Subunits - metabolism; Proton-Translocating ATPases - chemistry; Proton-Translocating ATPases - isolation & purification; Proton-Translocating ATPases - metabolism; Sequence Alignment; Static Electricity; Structural Homology, Protein; Temperature; F1-ATPase; inhibition; Caldalkalibacillus thermarum; regulation; structure
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1612035113

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.