bims-resufa 2020-07-05 papers

Issue of 2020–07–05
three papers selected by
Vera Strogolova, Marquette University

Sci Rep. 2020 Jun 29. 10(1): 10304

Protonic Capacitor: Elucidating the biological significance of mitochondrial cristae formation.

For decades, it was not entirely clear why mitochondria develop cristae? The work employing the transmembrane-electrostatic proton localization theory reported here has now provided a clear answer to this fundamental question. Surprisingly, the transmembrane-electrostatically localized proton concentration at a curved mitochondrial crista tip can be significantly higher than that at the relatively flat membrane plane regions where the proton-pumping respiratory supercomplexes are situated. The biological significance for mitochondrial cristae has now, for the first time, been elucidated at a protonic bioenergetics level: 1) The formation of cristae creates more mitochondrial inner membrane surface area and thus more protonic capacitance for transmembrane-electrostatically localized proton energy storage; and 2) The geometric effect of a mitochondrial crista enhances the transmembrane-electrostatically localized proton density to the crista tip where the ATP synthase can readily utilize the localized proton density to drive ATP synthesis.

DOI: https://doi.org/10.1038/s41598-020-66203-6

J Cell Biol. 2020 Aug 03. pii: e202003131. [Epub ahead of print]219(8):

Phospholipid ebb and flow makes mitochondria go.

Michelle Grace Acoba, Nanami Senoo, Steven M Claypool.

Mitochondria, so much more than just being energy factories, also have the capacity to synthesize macromolecules including phospholipids, particularly cardiolipin (CL) and phosphatidylethanolamine (PE). Phospholipids are vital constituents of mitochondrial membranes, impacting the plethora of functions performed by this organelle. Hence, the orchestrated movement of phospholipids to and from the mitochondrion is essential for cellular integrity. In this review, we capture recent advances in the field of mitochondrial phospholipid biosynthesis and trafficking, highlighting the significance of interorganellar communication, intramitochondrial contact sites, and lipid transfer proteins in maintaining membrane homeostasis. We then discuss the physiological functions of CL and PE, specifically how they associate with protein complexes in mitochondrial membranes to support bioenergetics and maintain mitochondrial architecture.

DOI: https://doi.org/10.1083/jcb.202003131

Biochim Biophys Acta Bioenerg. 2020 Jun 26. pii: S0005-2728(20)30101-8. [Epub ahead of print] 148251

Comparative assessment of purified saponins as permeabilization agents during respirometry.

Corinna Dawid, Daniela Weber, Eva Musiol, Vanessa Janas, Sebastian Baur, Roman Lang, Tobias Fromme.

Saponins are a diverse group of secondary plant metabolites, some of which display hemolytic toxicity due to plasma membrane permeabilization. This feature is employed in biological applications for transferring hydrophilic molecules through cell membranes. Widely used commercial saponins include digitonin and saponins from soap tree bark, both of which constitute complex mixtures of little definition. We assessed the permeabilization power of pure saponins towards cellular membranes in an effort to detect novel properties and to improve existing applications. In a respirometric assay, we characterized half-maximal permeabilization of the plasma membrane for different metabolites, of the mitochondrial outer membrane for cytochrome C and the full solubilization of mitochondrial inner membrane protein complexes. Beyond the complete list as repository for the field, we highlight several findings with direct applicability. First, we identified and validated α-chaconine as alternative permeabilization agent in respirometric assays of cultured cells and isolated synaptosomes, superior to digitonin in its tolerability for mitochondria. Second, we identified glycyrrhizic acid to form exceptionally small pores impermeable for adenosine diphosphate. Third, in a concentration dependent manner, tomatine proved to be able to selectively permeabilize the mitochondrial outer, but not inner membrane, allowing for novel states in which to determine cytochrome C oxidase activity. In summary, we provide a list of the permeabilization properties of 18 pure saponins. The identification of two saponins, namely tomatine and chaconine, with direct usability in improved or novel cell biological applications within this small subgroup demonstrates the tremendous potential for further functional screening of pure saponins.

Keywords: Chaconine; Digitonin; Membrane permeabilization; Mitochondria; Respirometry; Saponin

DOI: https://doi.org/10.1016/j.bbabio.2020.148251