A computational study to assess the pathogenicity of single or combinations of missense variants on respiratory complex I.

Variants found in the respiratory complex I (CI) subunit genes encoded by mitochondrial DNA can cause severe genetic diseases. However, it is difficult to establish a priori whether a single or a combination of CI variants may impact oxidative phosphorylation. Here we propose a computational approach based on coarse-grained molecular dynamics simulations aimed at investigating new CI variants. One of the primary CI variants associated with the Leber hereditary optic neuropathy (m.14484T>C/MT-ND6) was used as a test case and was investigated alone or in combination with two additional rare CI variants whose role remains uncertain. We found that the primary variant positioned in the E-channel region, which is fundamental for CI function, stiffens the enzyme dynamics. Moreover, a new mechanism for the transition between π- and α-conformation in the helix carrying the primary variant is proposed. This may have implications for the E-channel opening/closing mechanism. Finally, our findings show that one of the rare variants, located next to the primary one, further worsens the stiffening, while the other rare variant does not affect CI function. This approach may be extended to other variants candidate to exert a pathogenic impact on CI dynamics, or to investigate the interaction of multiple variants.

Genetic variants affecting NQO1 protein levels impact the efficacy of idebenone treatment in Leber hereditary optic neuropathy.

Idebenone, the only approved treatment for Leber hereditary optic neuropathy (LHON), promotes recovery of visual function in up to 50% of patients, but we can neither predict nor understand the non-responders. Idebenone is reduced by the cytosolic NAD(P)H oxidoreductase I (NQO1) and directly shuttles electrons to respiratory complex III, bypassing complex I affected in LHON. We show here that two polymorphic variants drastically reduce NQO1 protein levels when homozygous or compound heterozygous. This hampers idebenone reduction. In its oxidized form, idebenone inhibits complex I, decreasing respiratory function in cells. By retrospectively analyzing a large cohort of idebenone-treated LHON patients, classified by their response to therapy, we show that patients with homozygous or compound heterozygous NQO1 variants have the poorest therapy response, particularly if carrying the m.3460G>A/MT-ND1 LHON mutation. These results suggest consideration of patient NQO1 genotype and mitochondrial DNA mutation in the context of idebenone therapy.

Use of bacterial photosynthetic vesicles to evaluate the effect of ionic liquids on the permeability of biological membranes.

Ionic liquids (ILs) are salts composed of a combination of organic or inorganic cations and anions characterized by a low melting point, often below 100 °C. This property, together with an extremely low vapor pressure, low flammability and high thermal stability, makes them suitable for replacing canonical organic solvents, with a reduction of industrial activities impact on the environment. Although in the last decades the eco-compatibility of ILs has been extensively verified through toxicological tests performed on model organisms, a detailed understanding of the interaction of these compounds with biological membranes is far from being exhaustive. In this context, we have chosen to evaluate the effect of some ILs on native membranes by using chromatophores, photosynthetic vesicles that can be isolated from Rhodobacter capsulatus, a member of the purple non­sulfur bacteria. Here, carotenoids associated with the light-harvesting complex II, act as endogenous spectral probes of the transmembrane electrical potential (ΔΨ). By measuring through time-resolved absorption spectroscopy the evolution of the carotenoid band shift induced by a single excitation of the photosynthetic reaction center, information on the ΔΨ dissipation due to ionic currents across the membrane can be obtained. We found that some ILs cause a rather fast dissipation of the transmembrane ΔΨ even at low concentrations, and that this behavior is dose-dependent. By using two different models to analyze the decay of the carotenoid signals, we attempted to interpret at a mechanistic level the marked increase of ionic permeability caused by specific ILs.