bims-mimbat 2023-04-30 papers

Sci Signal. 2023 04 25. 16(782): eabi8948

MICU1 regulates mitochondrial cristae structure and function independently of the mitochondrial Ca2+ uniporter channel.

Dhanendra Tomar, Manfred Thomas, Joanne F Garbincius, Devin W Kolmetzky, Oniel Salik, Pooja Jadiya, Suresh K Joseph, April C Carpenter, György Hajnóczky, John W Elrod.

MICU1 is a calcium (Ca2+)-binding protein that regulates the mitochondrial Ca2+ uniporter channel complex (mtCU) and mitochondrial Ca2+ uptake. MICU1 knockout mice display disorganized mitochondrial architecture, a phenotype that is distinct from that of mice with deficiencies in other mtCU subunits and, thus, is likely not explained by changes in mitochondrial matrix Ca2+ content. Using proteomic and cellular imaging techniques, we found that MICU1 localized to the mitochondrial contact site and cristae organizing system (MICOS) and directly interacted with the MICOS components MIC60 and CHCHD2 independently of the mtCU. We demonstrated that MICU1 was essential for MICOS complex formation and that MICU1 ablation resulted in altered cristae organization, mitochondrial ultrastructure, mitochondrial membrane dynamics, and cell death signaling. Together, our results suggest that MICU1 is an intermembrane space Ca2+ sensor that modulates mitochondrial membrane dynamics independently of matrix Ca2+ uptake. This system enables distinct Ca2+ signaling in the mitochondrial matrix and at the intermembrane space to modulate cellular energetics and cell death in a concerted manner.

DOI: https://doi.org/10.1126/scisignal.abi8948

Proc Natl Acad Sci U S A. 2023 May 02. 120(18): e2221047120

Carbon dioxide/bicarbonate is required for sensitive inactivation of mammalian glyceraldehyde-3-phosphate dehydrogenase by hydrogen peroxide.

Christine C Winterbourn, Alexander V Peskin, Torsten Kleffmann, Rafael Radi, Paul E Pace.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) contains an active site Cys and is one of the most sensitive cellular enzymes to oxidative inactivation and redox regulation. Here, we show that inactivation by hydrogen peroxide is strongly enhanced in the presence of carbon dioxide/bicarbonate. Inactivation of isolated mammalian GAPDH by H2O2 increased with increasing bicarbonate concentration and was sevenfold faster in 25 mM (physiological) bicarbonate compared with bicarbonate-free buffer of the same pH. H2O2 reacts reversibly with CO2 to form a more reactive oxidant, peroxymonocarbonate (HCO4-), which is most likely responsible for the enhanced inactivation. However, to account for the extent of enhancement, we propose that GAPDH must facilitate formation and/or targeting of HCO4- to promote its own inactivation. Inactivation of intracellular GAPDH was also strongly enhanced by bicarbonate: treatment of Jurkat cells with 20 µM H2O2 in 25 mM bicarbonate buffer for 5 min caused almost complete GAPDH inactivation, but no loss of activity when bicarbonate was not present. H2O2-dependent GAPDH inhibition in bicarbonate buffer was observed even in the presence of reduced peroxiredoxin 2 and there was a significant increase in cellular glyceraldehyde-3-phosphate/dihydroxyacetone phosphate. Our results identify an unrecognized role for bicarbonate in enabling H2O2 to influence inactivation of GAPDH and potentially reroute glucose metabolism from glycolysis to the pentose phosphate pathway and NAPDH production. They also demonstrate what could be wider interplay between CO2 and H2O2 in redox biology and the potential for variations in CO2 metabolism to influence oxidative responses and redox signaling.

Keywords: glyceraldehyde-3-phosphate dehydrogenase; hydrogen peroxide; peroxymonocarbonate; redox regulation; thiol protein oxidation

DOI: https://doi.org/10.1073/pnas.2221047120

J Am Chem Soc. 2023 Apr 27.

Visualizing Cardiolipin In Situ with HKCL-1M, a Highly Selective and Sensitive Fluorescent Probe.

Wei Wang, Nai-Kei Wong, Siu-Lun Bok, You Xu, Yang Guo, Lu Xu, Meiling Zuo, Claudette M St Croix, Gaowei Mao, Alexandr Kapralov, Hülya Bayir, Valerian E Kagan, Dan Yang.

Reliable probing of cardiolipin (CL) content in dynamic cellular milieux presents significant challenges and great opportunities for understanding mitochondria-related diseases, including cancer, neurodegeneration, and diabetes mellitus. In intact respiring cells, selectivity and sensitivity for CL detection are technically demanding due to structural similarities among phospholipids and compartmental secludedness of the inner mitochondrial membrane. Here, we report a novel "turn-on" fluorescent probe HKCL-1M for detecting CL in situ. HKCL-1M displays outstanding sensitivity and selectivity toward CL through specific noncovalent interactions. In live-cell imaging, its hydrolyzed product HKCL-1 efficiently retained itself in intact cells independent of mitochondrial membrane potential (Δψm). The probe robustly co-localizes with mitochondria and outperforms 10-N-nonyl acridine orange (NAO) and Δψm-dependent dyes with superior photostability and negligible phototoxicity. Our work thus opens up new opportunities for studying mitochondrial biology through efficient and reliable visualization of CL in situ.

DOI: https://doi.org/10.1021/jacs.3c00243

Commun Chem. 2023 Apr 22. 6(1): 77

Search for a Grotthuss mechanism through the observation of proton transfer.

Ivan Popov, Zhenghao Zhu, Amanda R Young-Gonzales, Robert L Sacci, Eugene Mamontov, Catalin Gainaru, Stephen J Paddison, Alexei P Sokolov.

The transport of protons is critical in a variety of bio- and electro-chemical processes and technologies. The Grotthuss mechanism is considered to be the most efficient proton transport mechanism, generally implying a transfer of protons between 'chains' of host molecules via elementary reactions within the hydrogen bonds. Although Grotthuss proposed this concept more than 200 years ago, only indirect experimental evidence of the mechanism has been observed. Here we report the first experimental observation of proton transfer between the molecules in pure and 85% aqueous phosphoric acid. Employing dielectric spectroscopy, quasielastic neutron, and light scattering, and ab initio molecular dynamic simulations we determined that protons move by surprisingly short jumps of only ~0.5-0.7 Å, much smaller than the typical ion jump length in ionic liquids. Our analysis confirms the existence of correlations in these proton jumps. However, these correlations actually reduce the conductivity, in contrast to a desirable enhancement, as is usually assumed by a Grotthuss mechanism. Furthermore, our analysis suggests that the expected Grotthuss-like enhancement of conductivity cannot be realized in bulk liquids where ionic correlations always decrease conductivity.

DOI: https://doi.org/10.1038/s42004-023-00878-6