Cryo-EM studies of the rotary H+-ATPase/synthase from Thermus thermophilus

Proton-translocating rotary ATPases couple proton influx across the membrane domain and ATP hydrolysis/synthesis in the soluble domain through rotation of the central rotor axis against the surrounding peripheral stator apparatus. It is a significant challenge to determine the structure of rotary ATPases due to their intrinsic conformational heterogeneity and instability. Recent progress of single particle analysis of protein complexes using cryogenic electron microscopy (cryo-EM) has enabled the determination of whole rotary ATPase structures and made it possible to classify different rotational states of the enzymes at a near atomic resolution. Three cryo-EM maps corresponding to different rotational states of the V/A type H+-rotary ATPase from a bacterium Thermus thermophilus provide insights into the rotation of the whole complex, which allow us to determine the movement of each subunit during rotation. In addition, this review describes methodological developments to determine higher resolution cryo-EM structures, such as specimen preparation, to improve the image contrast of membrane proteins.