bims-cytox1 2023-08-06 papers

Issue of 2023‒08‒06
two papers selected by
Gavin McStay
Liverpool John Moores University

Nature. 2023 Aug 01.

Central role of Tim17 in mitochondrial presequence protein translocation.

Laura F Fielden, Jakob D Busch, Sandra G Merkt, Iniyan Ganesan, Conny Steiert, Hanna B Hasselblatt, Jon V Busto, Christophe Wirth, Nicole Zufall, Sibylle Jungbluth, Katja Noll, Julia M Dung, Ludmila Butenko, Karina von der Malsburg, Hans-Georg Koch, Carola Hunte, Martin van der Laan, Nils Wiedemann.

The presequence translocase of the mitochondrial inner membrane (TIM23) represents the major route for the import of nuclear-encoded proteins into mitochondria1,2. About 60% of more than 1,000 different mitochondrial proteins are synthesised with amino-terminal targeting signals, termed presequences, which form positively charged amphiphilic α-helices3,4. TIM23 sorts the presequence proteins into the inner membrane or matrix. Various views including regulatory and coupling functions have been reported on the essential TIM23 subunit Tim175-7. We mapped the interaction of Tim17 with matrix-targeted and inner membrane-sorted preproteins during translocation in the native membrane environment. We show that Tim17 contains conserved negative charges close to the intermembrane space side of the bilayer, which are essential to initiate presequence protein translocation along a distinct transmembrane cavity of Tim17 for both classes of preproteins. The amphiphilic character of mitochondrial presequences directly matches this Tim17-dependent translocation mechanism. This mechanism permits direct lateral release of transmembrane segments of inner membrane-sorted precursors into the inner membrane.

DOI: https://doi.org/10.1038/s41586-023-06477-8

Biochim Biophys Acta Bioenerg. 2023 Jul 27. pii: S0005-2728(23)00046-4. [Epub ahead of print]1864(4): 149000

The catalytic reaction of cytochrome c oxidase probed by in situ gas titrations and FTIR difference spectroscopy.

Federico Baserga, Julian Storm, Ramona Schlesinger, Joachim Heberle, Sven T Stripp.

Cytochrome c oxidase (CcO) is a transmembrane heme‑copper metalloenzyme that catalyzes the reduction of O2 to H2O at the reducing end of the respiratory electron transport chain. To understand this reaction, we followed the conversion of CcO from Rhodobacter sphaeroides between several active-ready and carbon monoxide-inhibited states via attenuated total reflection Fourier-transform infrared (ATR FTIR) difference spectroscopy. Utilizing a novel gas titration setup, we prepared the mixed-valence, CO-inhibited R2CO state as well as the fully-reduced R4 and R4CO states and induced the "active ready" oxidized state OH. These experiments are performed in the dark yielding FTIR difference spectra exclusively triggered by exposure to O2, the natural substrate of CcO. Our data demonstrate that the presence of CO at heme a3 does not impair the catalytic oxidation of CcO when the cycle starts from the fully-reduced states. Interestingly, when starting from the R2CO state, the release of the CO ligand upon purging with inert gas yield a product that is indistinguishable from photolysis-induced states. The observed changes at heme a3 in the catalytic binuclear center (BNC) result from the loss of CO and are unrelated to electronic excitation upon illumination. Based on our experiments, we re-evaluate the assignment of marker bands that appear in time-resolved photolysis and perfusion-induced experiments on CcO.

Keywords: Carbon monoxide; Cytochrome c oxidase; Infrared spectroscopy; Ligation; Nanodiscs

DOI: https://doi.org/10.1016/j.bbabio.2023.149000