br Conclusion GroEL from RA CH was expressed and purified

Conclusion GroEL from RA-CH-1 was expressed and purified. The recombinant RaGroEL protein exhibited ATPase activity, which cooperated with GroES in ATP hydrolysis. Furthermore, the expression pattern of groEL revealed that groEL was up-regulated during stress response. Further studies are warranted to elucidate the molecular mechanism of GroEL proteins as molecular chaperones in environmental stress responses.
Conflicts of interest
Acknowledgements
Introduction The bioenergetics of saccharolytic bacteria, such as Escherichia coli, have been extensively studied. It has been established that the proton gradient across the bacterial plasma membrane is important for cell physiology, mainly the ATP synthesis [1]. On the other hand, bioenergetics of asaccharolytic anaerobes, including Porphyromonas gingivalis and Porphyromonas endodontalis, have not been fully elucidated because of experimental difficulties. The growth of these bacteria is not dependent on hydrocarbons, but on hydroxychloroquine sulfate or peptides [2]. Thus, uncovering the role of the ion gradient in energy metabolism that relies on these nutrients, or more fundamentally, investigating whether the gradient is essential for these bacteria, is of interest. Periodontitis is a chronic inflammatory disease of the periodontal tissue. Progressive periodontitis leads to alveolar bone resorption. Increasing evidence suggests that the disease also plays a role in various pathologies, including rheumatoid arthritis, diabetes, and cardiovascular disease [[3], [4], [5]]. P. gingivalis, a Gram-negative asaccharolytic anaerobe, is a major causative agent of periodontitis. Thus, studies of this bacterium are important for the development of drugs targeting periodontitis and systemic diseases. P. gingivalis transports amino acids and oligopeptides across the plasma membrane to generate energy [6]. It is believed that a proton and/or sodium gradient generates an essential motive force for the transport of these nutrients [6,7]. The gradient is also utilized for iron uptake, resistance against antimicrobial agents, and ATP synthesis [[8], [9], [10]]. Proton-pumping ATPases located in the bacterial membrane transport protons from the cytoplasm to the periplasm, coupling with ATP hydrolysis, which results in the formation of the proton gradient. F-type ATPases (F-ATPases) and A-type ATPases (A-ATPases) are proton-pumping ATPases of the bacterial membrane. X-ray crystallography and electron microscopy analyses of the two ATPases revealed that they have similar tertiary structure, which is formed by a catalytic domain (F1/A1) and a proton channel-forming domain (FO/AO) [11]. The F-ATPase is found in most bacteria, including E. coli and Mycobacterium tuberculosis. This enzyme is also called ATP synthase and mainly functions in ATP synthesis under aerobic conditions. On the other hand, the A-ATPase was originally identified in archaea, including Methanosarcina mazei and Pyrococcus furiosus [11]. This ATPase can form an ion gradient essential for nutrient import, and some reports suggest that it also synthesizes ATP. P. gingivalis likely possesses a functional A-ATPase, since its chromosome harbors a gene cluster of reading frames for a protein similar to a Thermus thermophilus A-ATPase [10]. Various aspects of the F-ATPase have been extensively studied, from its enzymatic mechanism to clinical applications. Others and our group reported that, in the F-ATPases of E. coli and thermophilic Bacillus, the catalysis that takes place in the F1 domain is coupled with proton transport in the FO domain via subunit rotation [[12], [13], [14], [15], [16]]. The mechanism of the rotational catalysis has been revealed in detail. We also reported that curcumin and its analogues inhibit the growth of E. coli by inhibiting its F-ATPase [17,18]. As for clinical applications, bedaquiline, an inhibitor of the M. tuberculosis F-ATPase, has been approved as an antituberculosis agent [19].