Subunit epsilon of E. coli F1Fo ATP synthase attenuates enzyme activity by modulating central stalk flexibility

ABSTRACTF1Fo ATP synthase functions as a biological rotary generator that makes a major contribution to cellular energy production. Proton flow through the Fo motor generates rotation of the central stalk, inducing conformational changes in the F1 motor that catalyzes ATP production via flexible coupling. Here we present a range of cryo-EM structures of E. coli ATP synthase in different rotational and inhibited states observed following a 45 second incubation with 10 mM MgATP. The structures generated describe multiple changes that occur following addition of MgATP, with the inhibitory C-terminal domain of subunit ε (εCTD) disassociating from the central stalk to adopt a condensed “down” conformation. The transition to the εCTD down state increases the torsional flexibility of the central stalk allowing its foot to rotate by ∼50°, with further flexing in the peripheral stalk enabling the c-ring to rotate by two sub-steps in the Fo motor. Truncation mutants lacking the second helix of the εCTD suggest that central stalk rotational flexibility is important for F1Fo ATP synthase function. Overall this study identifies the potential role played by torsional flexing within the rotor and how this could be influenced by the ε subunit.

Effects of Morphological and Anatomical Characteristics of Banana Crown Vascular Bundles on Cutting Mechanical Properties Using Multiple Imaging Methods

To obtain the appropriate mechanized cutting region for banana dehanding, the methods of X-ray Computed Tomography (CT), Paraffin-embedded tissue section, and scanning electron microscopy (SEM) were adopted to observe the morphological and anatomical characteristics of vascular bundles of the banana crown. The results indicated that the crown can be divided into three regions, viz., the central stalk–crown transition region (CSCTR), the crown expansion region (CER), and the crown–finger transition region (CFTR). According to the obtained characteristics, the cutting mechanical properties are found to be affected by the relative angle between the vascular bundle and cutter (RAVBC) and the vascular bundle density. In CSCTR, due to the opposite change of RAVBC and density, the cutting mechanical properties become unstable and the cutting energy decreases gradually from 4.30 J to 2.57 J. While in CER, the cutting mechanical properties tend to be stable, and the cutting energy varies in a small range (2.83–2.92 J), owing to the small changes of RAVBC and density. When the vascular bundles cross from the CER to CFTR, the cutting energy increases with the increase of RAVBC and density, which varies from 3.37 to 4.84 J. Accordingly, the appropriate cutting region for dehanding, which can reduce the energy consumption and improve the cutting efficiency, is ascertained to be between CSCTR and CER.

Nutrient contents and in vitro digestibility of different parts of corn plant

The objective of this study was to assess the nutrient contents and in vitro true digestibility (IVTD) of parts of the corn plant. The corn used in the study was P2088, a variety that is grown widely in Turkey. It had matured and was harvested 140 days after planting. Four replicate plants were separated into nine parts, namely lower stalk, central stalk, upper stalk, corn ear stalk, corn ear shuck, kernels, corn cob, leaf, tassel, plus the entire plant. The samples were dried and ground for analysis. Nutritional values were determined in the laboratory and in vitro digestibility was assessed. Significant differences in nutrient content were observed among parts of the corn plant. The highest crude protein (CP) content was found in the leaf (12.41%), followed by the grain (12.37%). Dry matter (DM) varied from 91.25% to 96.07%. The highest ether extract (EE) was in the grain (2.84%), and the upper stalk contained the least EE (0.29%). The parts also differed in their contents of crude cellulose (CS) and crude ash (CA) (P <0.001). Most organic matter (OM) was found in the corn cup (94.27%). The highest in vitro dry matter digestibility (IVDMD) was in the kernels (79.06%) and the lowest was in the lower stalk (38.13%). In terms of in vitro true organic matter digestibility (OMD) values of the corn plant and its 9 parts, the highest values were found in the kernels and the lowest in the lower stalk.Keywords: crude nutrients, in vitro true digestibility, parts of corn plant

The β-hairpin region of the cyanobacterial F1-ATPase γ-subunit plays a regulatory role in the enzyme activity

The γ-subunit of cyanobacterial and chloroplast ATP synthase, the rotary shaft of F1-ATPase, equips a specific insertion region that is only observed in photosynthetic organisms. This region plays a physiologically pivotal role in enzyme regulation, such as in ADP inhibition and redox response. Recently solved crystal structures of the γ-subunit of F1-ATPase from photosynthetic organisms revealed that the insertion region forms a β-hairpin structure, which is positioned along the central stalk. The structure–function relationship of this specific region was studied by constraining the expected conformational change in this region caused by the formation of a disulfide bond between Cys residues introduced on the central stalk and this β-hairpin structure. This fixation of the β-hairpin region in the α3β3γ complex affects both ADP inhibition and the binding of the ε-subunit to the complex, indicating the critical role that the β-hairpin region plays as a regulator of the enzyme. This role must be important for the maintenance of the intracellular ATP levels in photosynthetic organisms.

Rotary substates of mitochondrial ATP synthase reveal the basis of flexible F1-Focoupling

F1Fo–adenosine triphosphate (ATP) synthases make the energy of the proton-motive force available for energy-consuming processes in the cell. We determined the single-particle cryo–electron microscopy structure of active dimeric ATP synthase from mitochondria ofPolytomellasp. at a resolution of 2.7 to 2.8 angstroms. Separation of 13 well-defined rotary substates by three-dimensional classification provides a detailed picture of the molecular motions that accompanyc-ring rotation and result in ATP synthesis. Crucially, the F1head rotates along with the central stalk andc-ring rotor for the first ~30° of each 120° primary rotary step to facilitate flexible coupling of the stoichiometrically mismatched F1and Fosubcomplexes. Flexibility is mediated primarily by the interdomain hinge of the conserved OSCP subunit. A conserved metal ion in the proton access channel may synchronizec-ring protonation with rotation.

Visualizing movements in E. coli F1Fo ATP synthase indicates how the F1 and Fo motors are coupled

F1Fo ATP synthase functions as a biological rotary generator and makes a major contribution to cellular energy production. It is comprised of two motors that are coupled together by a central “rotor” and peripheral “stator” stalk. Proton flow through the Fo motor generates rotation of the central stalk that induces conformation changes that catalyze production of ATP in the F1 motor. Here we provide 3-4 Å resolution cryo-EM structures of E. coli F1Fo ATP synthase in 10 mM MgADP. In addition to generating a comprehensive structural model of E. coli F1Fo ATP synthase to provide a framework to interpret mutagenesis studies, we describe a rotational sub-step of the Fo motor c-ring associated with long-range conformational changes that suggests an elegant mechanism by which the F1 and Fo motors can be coupled with minimal energy loss.