[Frontier Leaders] CryoEM of mitochondrial membrane protein complexes

Frontier Leaders Seminar

Title: CryoEM of mitochondrial membrane protein complexes

Speaker: Werner Kühlbrant

Affiliation: Max Planck Institute of Biophysics, Department of Structural Biology, Frankfurt am Main, Germany | Director of the institute, pioneer in cryo-EM and Tomography

Abstract:

The advent of new direct electron detectors for electron cryo-microscopy (cryoEM) is having an enormous impact on the structure determination of large, flexible protein complexes that were previously out of reach (Kühlbrandt, 2014). Single-particle cryoEM of mitochondrial ATP synthase dimers revealed a pair of long, membrane-intrinsic helices in subunit a of two different mitochondrial ATP synthase dimers adjacent to the c-ring rotor (Allegretti et al, 2015; Hahn et al, 2016). The helices are a fundamental feature of all rotary ATPases and play a key role in proton transfer (Kühlbrandt & Davies, 2016).  By electron cryo-tomography (cryoET) of mitochondria from a wide range of organisms (Davies et al, 2012; Mühleip et al, 2016; 2017) we found that rows of ATP synthase dimers along cristae ridges are a conserved, universal feature of inner membrane organization. By single-particle cryoEM we discovered an unexpected functional asymmetry in the respiratory supercomplex I1III2IV1 from bovine mitochondria (Sousa et al, 2016). CryoET revealed that the interaction of complex I with the complex III dimer in the supercomplex is conserved across all species, and thus appears to be essential for effective energy conversion in mitochondria. Recently, we determined the cryoEM structure of the twin-pore protein translocase TOM that transports more than 1000 different pre-proteins from the cytoplasm into mitochondria (Bausewein et al, 2017). In the TOM complex, two 19-strand beta barrels of the Tom40 subunit, which resemble the mitochondrial VDAC anion channel, are surrounded by small, trans-membrane Tom subunits and held together by the tilted helices of the pre-protein import receptor Tom22.   

References

• 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.
• Bausewein T, Mills DJ, Langer JD, Nitschke B, Nussberger S & Kühlbrandt W (2017). Cryo-EM structure of the TOM core complex from Neurospora crassa. Cell 170: 693-700.
• 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., Parey, K., Bublitz, M., Mills, D.J., Zickermann, V., Vonck, J., Kühlbrandt, W. and Meier, T. (2016). Structure of a complete ATP synthase dimer reveals the molecular basis of inner mitochondrial membrane morphology. Mol Cell 63, 445-456.
• Kühlbrandt, W. (2014). The resolution revolution. Science 343, 1443–1444.
• Kühlbrandt, W., & Davies, K. M. (2016). Rotary ATPases: A new twist to an ancient machine. Trends in Biochemical Sciences, 41(1), 106–116.
• 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 (30), 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 doi:10.1073/pnas.1612386114.
• Sousa, J. S., Mills, D. J., Vonck, J., & Kühlbrandt, W. (2016). Functional asymmetry and electron flow in the bovine respirasome. eLife 5, e21290. doi:10.7554/eLife.21290.