Feodor Lynen Lecture:
Mechanistic insights from high-resolution cryoEM structures of ATP synthases
Max Planck Institute of Biophysics, Department of Structural Biology, Max-von-Laue Str. 3, 60438 Frankfurt am Main, Germany.
With the ongoing resolution revolution in electron cryo-microscopy (cryoEM; Kühlbrandt, 2014), large and dynamic membrane protein complexes have become accessible to high-resolution structural studies. We have used single-particle cryoEM to determine the structure of the complete, monomeric ATP synthase (cF1Fo) from spinach chloroplasts (Hahn et al, 2018), and of the dimeric mitochondrial F1Fo ATP synthase (mtF1Fo) from the green alga Polytomella (Allegretti et al, 2015; Klusch et al, 2017), both at around 3 Å resolution. Bound nucleotides with their coordinating Mg ions and water molecules are resolved in cF1. The two-domain subunit δ of cF1Fo (OSCP in mitochondria) joins the three α-subunits of the F1 head to the peripheral stalk in three different ways. Three resolved rotary states of cF1Fo indicate that the peripheral stalk flexes to store torsional energy, whereas subunit γ of the central stalk works as a non-flexible rigid body. In both mitochondria and chloroplasts, subunit a in the membrane-embedded Fo motor forms two aqueous channels to conduct protons to and from the protonation sites on the c-ring rotor that powers ATP generation. The channels and the polar and charged sidechains that define them in the hydrophobic membrane interior are conserved over an evolutionary distance of around 1.5 billion years (Kühlbrandt, 2019). The Fo motor assembly with its hairpin of long, membrane-embedded subunit a helices adapts equally well to the 10-subunit c-ring of mtF1Fo and the 14-subunit c-ring of cF1Fo. Electron cryo-tomography of chloroplast thylakoids indicated that cF1Fo is always monomeric, whereas all mtF1Fo dimers form rows that impose high local membrane curvature on the inner membrane (Davies et al, 2012; Mühleip et al, 2016; 2017). When reconstituted into proteoliposomes, ATP synthase dimers assemble into rows spontaneously, inducing high local membrane curvature as in mitochondria (Blum et al, 2019; Kühlbrandt, 2019).
Allegretti, M., Klusch, N., Mills, D.J., Vonck, J., Kühlbrandt, W. & Davies, K.M. (2015). Horizontal membrane-intrinsic α-helices in the stator a-subunit of an F-type ATP synthase. Nature 521, 237-240.
Blum T. B., Hahn A., Meier T., Davies K.M., Kühlbrandt W. (2019). Dimers of mitochondrial ATP synthase induce membrane curvature and self-assemble into rows. Manuscript under revision .
Davies, K.M., Anselmi, C., Wittig, I., Faraldo-Gómez, J.D., Kühlbrandt, W. (2012). Structure of the yeast F1Fo-ATP synthase dimer and its role in shaping the mitochondrial cristae. PNAS 109, 13602-13607.
Hahn, A., Vonck, J., Mills, D.J., Meier, T. Kühlbrandt, W. (2018). Structure, mechanism and regulation of the chloroplast ATP synthase. Science 360, eaat4318.
Klusch, N., Murphy, B. J., Mills, D. J., Yildiz, O., & Kühlbrandt, W. (2017). Structural basis of proton translocation and force generation in mitochondrial ATP synthase. eLife 6, doi:10.7554/eLife.33274
Kühlbrandt, W. (2014). The resolution revolution. Science 343, 1443–1444.
Kühlbrandt, W. (2019). Structure and mechanisms of F-type ATP synthases. Annu Rev Biochem 88, in press.
Mühleip, A. W., Joos, F., Wigge, C., Frangakis, A. S., Kühlbrandt, W., & Davies, K. M. (2016). Helical arrays of U-shaped ATP synthase dimers form tubular cristae in ciliate mitochondria. PNAS 113, 8442–8447.
Mühleip, A. W., Dewar, C. E., Schnaufer, A., Kühlbrandt, W., & Davies, K. M. (2017). In situ structure of trypanosomal ATP synthase dimer reveals a unique arrangement of catalytic subunits. PNAS 114, 992-997