Membrane-Anchored Cyclic Peptides as Effectors of Mitochondrial Oxidative Phosphorylation

Abstract

The echinocandins are membrane-anchored, cyclic lipopeptides (CLPs) with antifungal activity due to their ability to inhibit a glucan synthase located in the plasma membrane of fungi such as Candida albicans. A hydrophobic tail of an echinocandin CLP inserts into a membrane, placing a six-amino acid cyclic peptide near the membrane surface. Because processes critical for the function of the electron transfer complexes of mitochondria, such as proton uptake and release, take place near the surface of the membrane, we have tested the ability of two echinocandin CLPs, caspofungin and micafungin, to affect the activity of electron transfer complexes in isolated mammalian mitochondria. Indeed, caspofungin and micafungin both inhibit whole chain electron transfer in isolated mitochondria at low micromolar concentrations. The effects of the CLPs are fully reversible, in some cases simply via the addition of bovine serum albumin to bind the CLPs via their hydrophobic tails. Each CLP affects more than one complex, but they still exhibit specificity of action. Only caspofungin inhibits complex I, and the CLP inhibits liver but not heart complex I. Both CLPs inhibit heart and liver complex III. Caspofungin inhibits complex IV activity, while, remarkably, micafungin stimulates complex IV activity nearly 3-fold. Using a variety of assays, we have developed initial hypotheses for the mechanisms by which caspofungin and micafungin alter the activities of complexes IV and III. The dication caspofungin partially inhibits cytochrome c binding at the low-affinity binding site of complex IV, while it also appears to inhibit the release of protons from the outer surface of the complex, similar to Zn(2+). Anionic micafungin appears to stimulate complex IV activity by enhancing the transfer of protons to the O2 reduction site. For complex III, we hypothesize that each CLP binds to the cytochrome b subunit and the Fe-S subunit to inhibit the required rotational movement of the latter.

PKM2, function and expression and regulation

“…These REDOX equivalents can be combined with fatty acid metabolism, amino acid replenishment, and reducing equivalents in the tricarboxylic acid cycle to form a REDOX equivalent pool [26, 27], while providing a carbon source for tumor cell proliferation, at the same time part of these REDOX equivalents will participate in the biosynthesis of tumor cells [28, 29], and the other part will bypass the TCA cycle and directly oxidize and phosphorylate to supply cells with ATP (Fig. 1 the section of purple part) [30]. Through fatty acid metabolism, protein metabolism and tricarboxylic acid cycle synergy to supplied hydrogen ions jointly maintain the membrane potential of the mitochondria and maintain the operation of the electron transport chain [21, 31].…”

Uncoupling protein 3 deficiency impairs myocardial fatty acid oxidation and contractile recovery following ischemia/reperfusion

“…Heart mitochondria were isolated following previously established protocols with minor modifications [ 62 ]. In brief, cardiac tissue was minced with a razor blade in ice-cold MSM buffer supplemented with 1 mg/ml bacterial proteinase type XXIV (Nagarse).…”

Caspofungin induces the release of Ca2+ ions from internal stores by activating ryanodine receptor-dependent pathways in human tracheal epithelial cells

“…These findings imply that caspofungin has effects on other cell organelles. It may also interfere with mitochondrial ATP synthesis, as has been described for mammalian mitochondria 28 . Under these circumstances, the remaining ATP supply from mitochondria, glycolysis or phosphocreatine stores is too low to fully activate Ca 2+ ATPase in the plasma membrane.…”

“…In liver cells and cardiomyocytes, caspofungin is known to disturb the electron transport within the mitochondrial respiratory chain by inhibiting complex I and III. The effect on complex III is probably caused by its interference with cytochrome C 28 . However, it is not known whether this mechanism also depolarizes mitochondrial membrane potential, which is essential for Ca 2+ buffering in these organelles 9 .…”