AtCGL160 recruits chloroplast coupling factor 1

ATP synthases couple the generation of chemical energy to a transmembrane electro-chemical potential. Like ATP synthases in bacteria and mitochondria, chloroplast ATP synthases consist of a membrane-spanning (CFO) and a soluble coupling factor (CF1). Accessory factors facilitate subunit production and orchestrate the assembly of the functional CF1-CFO complex. It was previously shown that the accessory factor CGL160 promotes the formation of plant CFO and performs a similar function in the assembly of its c-ring to that of the distantly related bacterial Atp1/UncI protein. In this study, we show that the N-terminal portion of CGL160 (AtCGL160N), which is specific to the green lineage, is required for late steps in CF1-CFO assembly in Arabidopsis thaliana. In plants that lacked this stroma-exposed domain, photosynthesis was impaired, and amounts of CF1-CFO were reduced to about 65% of the wild-type level. Loss of AtCGL160N did not perturb c-ring formation, but led to a 10-fold increase in the numbers of CF1 sub-complexes in the stroma relative to the wild type and the CF1 assembly mutant atcgld11-1. Co-immunoprecipitation and protein crosslinking assays revealed an association of AtCGL160 with CF1 subunits. Yeast two-hybrid assays localized the interaction to a stretch of AtCGL160N that binds to the thylakoid-proximal domain of CF1-β that includes the conserved DELSEED motif. We therefore propose that AtCGL160 has acquired an additional function in the recruitment of soluble CF1 to a membrane-integral CFO sub-complex, which is critical for the modulation of CF1-CFO activity and photosynthesis in chloroplasts.

Rotor subunits adaptations in ATP synthases from photosynthetic organisms

Driven by transmembrane electrochemical ion gradients, F-type ATP synthases are the primary source of the universal energy currency, adenosine triphosphate (ATP), throughout all domains of life. The ATP synthase found in the thylakoid membranes of photosynthetic organisms has some unique features not present in other bacterial or mitochondrial systems. Among these is a larger-than-average transmembrane rotor ring and a redox-regulated switch capable of inhibiting ATP hydrolysis activity in the dark by uniquely adapted rotor subunit modifications. Here, we review recent insights into the structure and mechanism of ATP synthases specifically involved in photosynthesis and explore the cellular physiological consequences of these adaptations at short and long time scales.

Fast ATP-dependent subunit rotation in reconstituted FoF1-ATP synthase trapped in solution

ABSTRACTFoF1-ATP synthases are the ubiquitous membrane enzymes which catalyze ATP synthesis or ATP hydrolysis in reverse, respectively. Enzyme kinetics are controlled by internal subunit rotation, by substrate and product concentrations, by mechanical inhibitory mechanisms, but also by the electrochemical potential of protons across the membrane. By utilizing an Anti- Brownian electrokinetic trap (ABEL trap), single-molecule Förster resonance energy transfer (smFRET)-based subunit rotation monitoring was prolonged from milliseconds to seconds. The extended observation times for single proteoliposomes in solution allowed to observe fluctuating rotation rates of individual enzymes and to map the broad distributions of ATP-dependent catalytic rates in FoF1-ATP synthase. The buildup of an electrochemical potential of protons was confirmed to limit the maximum rate of ATP hydrolysis. In the presence of ionophores and uncouplers the fastest subunit rotation speeds measured in single reconstituted FoF1-ATP synthases were 180 full rounds per second, i.e. much faster than measured by biochemical ensemble averaging, but not as fast as the maximum rotational speed reported previously for isolated single F1 fragments without coupling to the membrane-embedded Fo domain of the enzyme.

Ordered Clusters of the Complete Oxidative Phosphorylation System in Cardiac Mitochondria

The existence of a complete oxidative phosphorylation system (OXPHOS) supercomplex including both electron transport system and ATP synthases has long been assumed based on functional evidence. However, no structural confirmation of the docking between ATP synthase and proton pumps has been obtained. In this study, cryo-electron tomography was used to reveal the supramolecular architecture of the rat heart mitochondria cristae during ATP synthesis. Respirasome and ATP synthase structure in situ were determined using subtomogram averaging. The obtained reconstructions of the inner mitochondrial membrane demonstrated that rows of respiratory chain supercomplexes can dock with rows of ATP synthases forming oligomeric ordered clusters. These ordered clusters indicate a new type of OXPHOS structural organization. It should ensure the quickness, efficiency, and damage resistance of OXPHOS, providing a direct proton transfer from pumps to ATP synthase along the lateral pH gradient without energy dissipation.

Bacterial F-type ATP synthases follow a well-choreographed assembly pathway

F-type ATP synthases are multiprotein complexes composed of two separate coupled motors (F1 and FO) generating adenosine triphosphate (ATP) as the universal major energy source in a variety of relevant biological processes in mitochondria, bacteria and chloroplasts. In the past decades, ATP synthases have become a subject of high interest, as a target for therapeutic use in the treatment of a variety of diseases. While the structure of many ATPases is solved today, the precise assembly pathway of F1FO-ATP synthases is mostly still unclear. To probe the bacterial F1 assembly of Acetobacterium woodii, we studied the self-assembly of purified proteins under different environments. We report assembly requirements, important assembly intermediates in vitro and in vivo, the crucial role of nucleotide binding (as opposed to ATP hydrolysis) and correlate results with complex activity. Finally, we propose a model for the assembly pathway for the formation of a functional F1 complex.