bims-resufa 2023-03-26 papers

Issue of 2023‒03‒26
two papers selected by
Vera Strogolova
Strong Microbials, Inc

FASEB J. 2023 Apr;37(4): e22891

Switching ubiquitous and muscle-specific isoforms of mitochondrial respiratory complex IV in skeletal muscle fine-tunes complex IV activity.

Xianglai Ye, Yaojun Xie, Yu Shi, Bo Wang, Xinyu Han, Xiaoxuan Zhou, Kexin Pan, Maofeng Wang, Hezhi Fang.

Respiratory complex IV (CIV, cytochrome c oxidase) is the terminal enzyme of the mitochondrial electron transport chain. Some CIV subunits have two or more isoforms, which are ubiquitously expressed or are expressed in specific tissues like the lung, muscle, and testis. Among the tissue-specific CIV isoforms, the muscle-specific isoforms are expressed in adult cardiac and skeletal muscles. To date, the physiological and biochemical association between the muscle-specific CIV isoforms and aerobic respiration in muscles remains unclear. In this study, we profiled the CIV organization and expression pattern of muscle-specific CIV isoforms in different mouse muscle tissues. We found extensive CIV-containing supramolecular organization in murine musculature at advanced developmental stages, while a switch in the expression from ubiquitous to muscle-specific isoforms of CIV was also detected. Such a switch was confirmed during the in vitro differentiation of mouse C2C12 myoblasts. Unexpectedly, a CIV expression decrease was observed during C2C12 differentiation, which was probably due to a small increase in the expression of muscle-specific isoforms coupled with a dramatic decrease in the ubiquitous isoforms. We also found that the enzymatic activity of CIV containing the muscle-specific isoform COX6A2 was higher than that with COX6A1 in engineered HEK293T cells. Overall, our results indicate that switching the expression from ubiquitous to muscle-specific CIV isoforms is indispensable for optimized oxidative phosphorylation in mature skeletal muscles. We also note that the in vitro C2C12 differentiation model is not suitable for the study of muscular aerobic respiration due to insufficient expression of muscle-specific CIV isoforms.

Keywords: electron transport complex IV; myoblasts; oxidative phosphorylation; protein isoforms; skeletal muscle

DOI: https://doi.org/10.1096/fj.202201223RR

Nature. 2023 Mar 22.

Structural basis of mitochondrial membrane bending by the I-II-III2-IV2 supercomplex.

Alexander Mühleip, Rasmus Kock Flygaard, Rozbeh Baradaran, Outi Haapanen, Thomas Gruhl, Victor Tobiasson, Amandine Maréchal, Vivek Sharma, Alexey Amunts.

Mitochondrial energy conversion requires an intricate architecture of the inner mitochondrial membrane1. Here we show that a supercomplex containing all four respiratory chain components contributes to membrane curvature induction in ciliates. We report cryo-electron microscopy and cryo-tomography structures of the supercomplex that comprises 150 different proteins and 311 bound lipids, forming a stable 5.8-MDa assembly. Owing to subunit acquisition and extension, complex I associates with a complex IV dimer, generating a wedge-shaped gap that serves as a binding site for complex II. Together with a tilted complex III dimer association, it results in a curved membrane region. Using molecular dynamics simulations, we demonstrate that the divergent supercomplex actively contributes to the membrane curvature induction and tubulation of cristae. Our findings highlight how the evolution of protein subunits of respiratory complexes has led to the I-II-III2-IV2 supercomplex that contributes to the shaping of the bioenergetic membrane, thereby enabling its functional specialization.

DOI: https://doi.org/10.1038/s41586-023-05817-y