Cells rely on protein complexes known as ATP synthases or ATPases for their energy requirements. Adenosine triphosphate (ATP) molecules drive most life-sustaining processes. The structural biologist Professor Leonid Sazanov and his research group from the Institute of Science and Technology Austria (IST Austria) in Klosterneuburg (Austria) have now determined the first atomic structure of the representative of the V / A-ATPase family and the gap in the evolutionary tree of this essential molecular Machinery. These results, obtained using the latest cryo-electron microscopy methods, demonstrated a turbine or water mills-like structure of the enzyme and have now been published in the journal Science .
ATP synthases / ATPases are large membrane protein complexes with common overall blueprint and rotational catalysis mechanisms. This protein family includes the F-type enzyme found in mitochondria (cell power plants), chloroplasts (organelles that photosynthesize plants), and bacteria; V (vacuolar) type in intracellular compartments of eukaryotes (higher organisms with one nucleus) and A (archaeal) type in prokaryotic archaea (ancient microorganisms) and some bacteria.
Different Flavors of ATPases
F and A enzymes normally produce ATP, driven by the proton flux through the membrane. V-type enzymes usually work in reverse and use ATP to pump protons. V and A ATPases are structurally similar, but differ in F-type by two or three peripheral stems and additional junction protein subunits between V1 and Vo. V-type enzymes have probably evolved from the A-type, and because of these similarities, the A-type is also referred to as V / A-ATPase. Some bacteria, including Thermus thermophilus acquired an A-type enzyme. Long Zhou, postdoctoral fellow in the Sazanov research group of IST Austria, has purified and investigated this enzyme (ThV1Vo) using cryo-EM. In contrast to the F type, only the structures of the isolated V 1 and V 0 domains were previously determined for V-type ATPases. It was therefore not known how V1 is coupled to Vo and lacked knowledge about the complete catalytic cycle.
Plasticity and Competition
The scientists determined not one but a total of five structures of the entire ThV1Vo enzyme using cryo-electron microscopy methods recently developed in the so-called "dissolution revolution" of this technique. The structures represent multiple conformational states of the enzyme that differ by the position of the rotor within the stator. The global conformational plasticity of ThV1Vo shows itself to be a significant wobble of V1 in space in the transition from one state to another. It is the result of mechanical competition between the rotation of the curved central rotor and the stiffness of the stator. The V1-Vo coupling is achieved by a close structural and electrostatic match between the wave and the V-type specific subunit connecting it to the C-ring. Visualization of the proton pathway revealed significant differences in the distribution of charged protein residues over F-ATPases, with a stricter "checkpoint" preventing "slipping" of the enzyme.
Why additional complexity?
Instead, of a single peripheral stem of F-type enzymes, A-types such as ThV1Vo have two peripheral peduncles, while eukaryotic V-types have three. But what is the advantage of additional complexity in the already very large protein array along with additional subunits that connect V1 and Vo? The F1 / V1 domain has a threefold symmetry such that one ATP molecule is generated (or consumed) per 120 ° turn of the stator in F1 / V1. Professor Leonid Sazanov says: "In V / A ATPases, this step is a one-off 120 ° turn, unlike F-ATP synthase, where it is divided into several sub-steps, so ThV1Vo may require more plasticity To link these 120 ° steps in V1 to smaller steps per c-subunit in the Vo c12 ring, this additional flexibility in V-types can be provided by the additional peripheral stems and connecting subunits.Our new structures show how this is achieved Providing a Framework for the Entire V-ATPase Family ".
Another puzzle piece of the ion pump
"Structure and conformational plasticity of the intact Thermus thermophilus ATPase of the V / A type" Science (2019). science.sciencemag.org/cgi/doi… 1126 / science.aaw9144
Structure of protein nanoturbine revealed (2019, August 22)
retrieved on 23rd August 2019
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