bims-mimbat 2024-11-10 papers

Issue of 2024‒11‒10
four papers selected by
José Carlos de Lima-Júnior, Washington University

Cell Calcium. 2024 Oct 23. pii: S0143-4160(24)00120-9. [Epub ahead of print]124 102962

Does a transmembrane sodium gradient control membrane potential in mammalian mitochondria?

In a recent publication, Hernansanz-Agusti̒n et al. propose that a sodium gradient across the inner mitochondrial membrane, generated by a Na+/H+ activity integral to Complex I can account for half of the mitochondrial membrane potential. This conflicts with conventional electrophysiological and chemiosmotic understanding.

Keywords: Calcium signaling; Goldman equation; Membrane potential; Mitochondria; Sodium proton exchange

DOI: https://doi.org/10.1016/j.ceca.2024.102962

Nature. 2024 Nov 06.

Cellular ATP demand creates metabolically distinct subpopulations of mitochondria.

Keun Woo Ryu, Tak Shun Fung, Daphne C Baker, Michelle Saoi, Jinsung Park, Christopher A Febres-Aldana, Rania G Aly, Ruobing Cui, Anurag Sharma, Yi Fu, Olivia L Jones, Xin Cai, H Amalia Pasolli, Justin R Cross, Charles M Rudin, Craig B Thompson.

Mitochondria serve a crucial role in cell growth and proliferation by supporting both ATP synthesis and the production of macromolecular precursors. Whereas oxidative phosphorylation (OXPHOS) depends mainly on the oxidation of intermediates from the tricarboxylic acid cycle, the mitochondrial production of proline and ornithine relies on reductive synthesis1. How these competing metabolic pathways take place in the same organelle is not clear. Here we show that when cellular dependence on OXPHOS increases, pyrroline-5-carboxylate synthase (P5CS)-the rate-limiting enzyme in the reductive synthesis of proline and ornithine-becomes sequestered in a subset of mitochondria that lack cristae and ATP synthase. This sequestration is driven by both the intrinsic ability of P5CS to form filaments and the mitochondrial fusion and fission cycle. Disruption of mitochondrial dynamics, by impeding mitofusin-mediated fusion or dynamin-like-protein-1-mediated fission, impairs the separation of P5CS-containing mitochondria from mitochondria that are enriched in cristae and ATP synthase. Failure to segregate these metabolic pathways through mitochondrial fusion and fission results in cells either sacrificing the capacity for OXPHOS while sustaining the reductive synthesis of proline, or foregoing proline synthesis while preserving adaptive OXPHOS. These findings provide evidence of the key role of mitochondrial fission and fusion in maintaining both oxidative and reductive biosyntheses in response to changing nutrient availability and bioenergetic demand.

DOI: https://doi.org/10.1038/s41586-024-08146-w

Methods Enzymol. 2024 ;pii: S0076-6879(24)00398-7. [Epub ahead of print]707 329-366

Analysis of mitochondrial translocases TOM and TIM by the patch-clamping technique.

María Luisa Campo.

Mitochondrial protein import and sorting relies on sophisticated molecular machineries or translocases, of which channels are integral. Channels are built upon membrane proteins whose functions are driven by conformational changes. This implies that structural and functional information need to be integrated to gain a deep understanding of their dynamic behavior. Patch-clamp approaches are well suited for this purpose. This chapter provides a detailed description and practical guidance for applying the patch-clamp methodology to the electrophysiological characterization of mitochondrial protein import. Implementing the technique to intact mitochondria, mitoplasts, and reconstituted proteoliposomes, combined with genetically modified yeast strains, expands the scope of these studies. Focused on the TOM, TIM23, and TIM22 translocases, an analysis of the patch-clamp contribution to the field is outlined.

Keywords: Mitochondria; Mitochondrial protein import; Patch-clamp; Protein import channels; TIM22 translocase; TIM23 translocase; TOM translocase

DOI: https://doi.org/10.1016/bs.mie.2024.07.053