Activation of succinate dehydrogenase by 2,4-dinitrophenol--a competitive inhibitor

Geldanamycin confers fungicidal properties to azole by triggering the activation of succinate dehydrogenase

AIMS

Azoles have been widely employed for the treatment of invasive fungal diseases; however, their efficacy is diminished as pathogenic fungi tolerate them due to their fungistatic properties. Geldanamycin (GdA) can render azoles fungicidal by inhibiting the ATPase and molecular chaperone activities of heat shock protein 90 (Hsp90). Nonetheless, the clinical applicability of GdA is restricted due to its cytotoxic ansamycin scaffold structure, its induction of cytoprotective heat shock responses, and the conservative nature of Hsp90. Hence, it is imperative to elucidate the mechanism of action of GdA to confer fungicidal properties to azoles and mitigate the toxic adverse effects associated with GdA.

MATERIALS AND METHODS

Through various experimental methods, including the construction of gene-deleted Candida albicans mutants, in vitro drug sensitivity experiments, Western blot analysis, reactive oxygen species (ROS) assays, and succinate dehydrogenase activity assays, we identified Hsp90 client proteins associated with the tolerance of C. albicans to azoles.

KEY FINDINGS

It was observed that GdA effectively hindered the entry of Hsp90 into mitochondria, resulting in the alleviation of inhibitory effect of Hsp90 on succinate dehydrogenase. Consequently, the activation of succinate dehydrogenase led to an increased production of ROS. within the mitochondria, thereby facilitating the antifungal effects of azoles against C. albicans.

SIGNIFICANCE

This research presents a novel approach for conferring fungicidal properties to azoles, which involves specifically disrupting the interaction of between Hsp90 and succinate dehydrogenase rather than employing a non-specific inhibition of ATPase activity of Hsp90.

Production cell analysis and compound-based boosting of small extracellular vesicle secretion using a generic and scalable production platform

Extracellular vesicles (EVs) are a novel format of advanced therapeutical medicinal products (ATMPs). They can act regenerative or immune-modulatory as cell therapy substitutes or as a platform for designer exosomes. The biotechnological production of therapeutic EVs is still very much uncharted territory so standardized host cells, production setups, and isolation methods are not yet implemented. In this work, we present a tangential flow filtration (TFF) and fast-performance liquid chromatography (FPLC)-based size exclusion chromatography (SEC) purification setup that is compatible for industry applications. Moreover, we evaluated a series of potential host cell lines regarding their EV productivity, characteristics, and biological functionality. It was found that telomerase-immortalized Wharton's jelly mesenchymal stromal cells (WJ-MSC/TERT273) secrete high amounts of EVs per cell with regenerative capabilities. On the other hand, Cevec's amniocyte producer cells® (CAP®) and human embryonic kidney (HEK293) suspension cells are suitable platforms for designer EVs with high yields. Finally, we aimed to boost the EV secretion of HEK293 cells via chemical adjuvants and verified four compounds that heighten cellular EV secretion in a presumably cAMP-dependent manner. A combination of fenoterol, iodoacetamide, and dinitrophenol increased the EV yield in HEK293 cells threefold and cellular secretion rate fivefold.

Structural and kinetic studies on the activators of succinate dehydrogenase

1. Diverse classes of compounds such as dicarboxylates, pyrophosphates, quinols and nitrophenols are known to activate mitochondrial succinate dehydrogenase (EC 1.3.99.1). Examples in each class -- malonate, pyrophosphate, ubiquinol and 2,4-dinitrophenol -- are selected for comparative studies on the kinetic constants and structural relationship. 2. The activated forms of the enzyme obtained on preincubating mitochondria with the effectors exhibited Michaelian kinetics and gave double-reciprocal plots which are nearly parallel to that of the basal form. On activation, Km for the substrate also increased along with V. The effectors activated the enzyme at low concentrations and inhibited, in a competitive fashion, at high concentrations. The binding constant for activation was lower than that for inhibition for each effector. 3. These compounds possess ionizable twin oxygens separated by a distance of 5.5 +/- 0.8 A and having fractional charges in the range of -0.26 to -0.74 e. The common twin-oxygen feature of the substrate and the effectors suggested the presence of corresponding counter charges in the binding domain. The competitive nature of effectors with the substrate for inhibition further indicated the close structural resemblance of the activation and catalytic sites.

Preparation of 1-acyl-2-succinyl glycero-3-phosphorylcholine and evidence against its involvement in succinate dehydrogenase action

1-Acyl-2-succinyl glycero-3-phosphorylcholine (GPC) was synthesized and its properties described. Although 1-acyl-2-succinyl GPC is a good substrate for succinate dehydrogenase, experiments on the incorporation of [2,3-14C] succinate into mitochondrial lipids gave no evidence to indicate that it is an intermediate in the enzymic oxidation of succinate to fumerate, as has been suggested earlier.

[Effects of thyroidectomy of the rat on the structure and functions of skeletal muscle mitochondria]

Mitochondria used in the present study were isolated from skeletal muscle of normal and thyroidectomized rats. The preparations were controlled by electron microscopy. It was not possible to find any morphological change induced by thyroidectomy, nevertheless, some difference appeared in the cytochrome contents which were slightly decreased. Oxygen consumption rates of thyroidectomized rat mitochondria were decreased when the particles were maintained in states 3 and 4 in the presence of various substrates, but the P/O ratios were not modified. The activities of mitochondrial enzymes were in general slightly affected by thyroidectomy except for glycerol-1-phosphate cytochrome c reductase and NADH rotenone sensitive cytochrome c reductase which were decreased and for glutamate dehydrogenase activity which was increased. The tRNA nucleotidyltransferase activity found in the mitochondrial matrix was not influenced by the absence of thyroid secretion. Normal rat muscle mitochondria incorporate 14C-leucine with an artificial ATP-generating system or with a respiratory substrate. The amino acid incorporation was decreased by thyroidectomy. Muscle mitochondria analyzed by polyacrylamide gel electrophoresis contained more than 30 protein components with MW ranging from 10.000 to 135.000. Thyroidectomy lowered the amount of a fraction of about 54.000 MW. It is not impossible that all the data observed in the absence of thyroid secretion are in relation with changes induced in the mitochondrial genome as previously shown in mitochondria isolated from liver or thyroidectomized rats.