bims-cytox1 2023-05-21 papers

Issue of 2023‒05‒21
two papers selected by
Gavin McStay
Liverpool John Moores University

IUBMB Life. 2023 May 13.

The role of the proteasome in mitochondrial protein quality control.

The abundance of each cellular protein is dynamically adjusted to the prevailing metabolic and stress conditions by modulation of their synthesis and degradation rates. The proteasome represents the major machinery for the degradation of proteins in eukaryotic cells. How the ubiquitin-proteasome system (UPS) controls protein levels and removes superfluous and damaged proteins from the cytosol and the nucleus is well characterized. However, recent studies showed that the proteasome also plays a crucial role in mitochondrial protein quality control. This mitochondria-associated degradation (MAD) thereby acts on two layers: first, the proteasome removes mature, functionally compromised or mis-localized proteins from the mitochondrial surface; and second, the proteasome cleanses the mitochondrial import pore of import intermediates of nascent proteins that are stalled during translocation. In this review, we provide an overview about the components and their specific functions that facilitate proteasomal degradation of mitochondrial proteins in the yeast Saccharomyces cerevisiae. Thereby we explain how the proteasome, in conjunction with a set of intramitochondrial proteases, maintains mitochondrial protein homeostasis and dynamically adapts the levels of mitochondrial proteins to specific conditions.

Keywords: mitochondria; mitochondria-associated degradation; proteasome; protein degradation; protein import; ubiquitin

DOI: https://doi.org/10.1002/iub.2734

Nat Commun. 2023 May 15. 14(1): 2783

Structural insights into cardiolipin replacement by phosphatidylglycerol in a cardiolipin-lacking yeast respiratory supercomplex.

Corey F Hryc, Venkata K P S Mallampalli, Evgeniy I Bovshik, Stavros Azinas, Guizhen Fan, Irina I Serysheva, Genevieve C Sparagna, Matthew L Baker, Eugenia Mileykovskaya, William Dowhan.

Cardiolipin is a hallmark phospholipid of mitochondrial membranes. Despite established significance of cardiolipin in supporting respiratory supercomplex organization, a mechanistic understanding of this lipid-protein interaction is still lacking. To address the essential role of cardiolipin in supercomplex organization, we report cryo-EM structures of a wild type supercomplex (IV1III2IV1) and a supercomplex (III2IV1) isolated from a cardiolipin-lacking Saccharomyces cerevisiae mutant at 3.2-Å and 3.3-Å resolution, respectively, and demonstrate that phosphatidylglycerol in III2IV1 occupies similar positions as cardiolipin in IV1III2IV1. Lipid-protein interactions within these complexes differ, which conceivably underlies the reduced level of IV1III2IV1 and high levels of III2IV1 and free III2 and IV in mutant mitochondria. Here we show that anionic phospholipids interact with positive amino acids and appear to nucleate a phospholipid domain at the interface between the individual complexes, which dampen charge repulsion and further stabilize interaction, respectively, between individual complexes.

DOI: https://doi.org/10.1038/s41467-023-38441-5