AtpΘ is an inhibitor of F0F1 ATP synthase to arrest ATP hydrolysis during low-energy conditions in cyanobacteria

• Published in: Current biology Vol. 32; no. 1; pp. 136 - 148.e5
• Main Authors: Song, Kuo, Baumgartner, Desirée, Hagemann, Martin, Muro-Pastor, Alicia M., Maaß, Sandra, Becher, Dörte, Hess, Wolfgang R.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 10.01.2022
• Subjects: cyanobacteria; F0F1 ATP synthase; inhibitor; Nostoc; proton gradient; redox regulation; small proteins; Synechocystis; thylakoid membranes; redox regulation; inhibitor; proton gradient; cyanobacteria; Nostoc; Synechocystis; thylakoid membranes; F0F1 ATP synthase; small proteins
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2021.10.051

Biological processes in all living cells are powered by ATP, a nearly universal molecule of energy transfer. ATP synthases produce ATP utilizing proton gradients that are usually generated by either respiration or photosynthesis. However, cyanobacteria are unique in combining photosynthetic and respiratory electron transport chains in the same membrane system, the thylakoids. How cyanobacteria prevent the futile reverse operation of ATP synthase under unfavorable conditions pumping protons while hydrolyzing ATP is mostly unclear. Here, we provide evidence that the small protein AtpΘ, which is widely conserved in cyanobacteria, is mainly fulfilling this task. The expression of AtpΘ becomes induced under conditions such as darkness or heat shock, which can lead to a weakening of the proton gradient. Translational fusions of AtpΘ to the green fluorescent protein revealed targeting to the thylakoid membrane. Immunoprecipitation assays followed by mass spectrometry and far western blots identified subunits of ATP synthase as interacting partners of AtpΘ. ATP hydrolysis assays with isolated membrane fractions, as well as purified ATP synthase complexes, demonstrated that AtpΘ inhibits ATPase activity in a dose-dependent manner similar to the F0F1-ATP synthase inhibitor N,N-dicyclohexylcarbodimide. The results show that, even in a well-investigated process, crucial new players can be discovered if small proteins are taken into consideration and indicate that ATP synthase activity can be controlled in surprisingly different ways. •AtpΘ is a small amphipathic protein in cyanobacteria encoded by the gene atpT•Conditions weakening the proton gradient trigger high atpT expression•AtpΘ is targeted to the thylakoids and coimmunoprecipitates with the ATP synthase•Activity assays show that AtpΘ is an inhibitor of ATP synthase ATPase activity ATP synthases produce ATP but can also run in reverse hydrolyzing ATP. Song et al. show that the small amphipathic protein AtpΘ is an inhibitor of the futile back reaction of ATP synthase in cyanobacteria, which operate ATP synthases, and photosynthetic and respiratory electron transport in the same membrane system.