Distinct properties of semiquinone species detected at the ubiquinol oxidation Q_{o} site of cytochrome bc_{1} and their mechanistic implications

The two-electron ubiquinol oxidation or ubiquinone reduction typically involves semiquinone (SQ) intermediates. Natural engineering of ubiquinone binding sites of bioenergetic enzymes secures that SQ is sufficiently stabilized, so that it does not leave the site to membranous environment before full oxidation/reduction is completed. The ubiquinol oxidation Q(o) site of cytochrome bc(1) (mitochondrial complex III, cytochrome b(6)f in plants) has been considered an exception with catalytic reactions assumed to involve highly unstable SQ or not to involve any SQ intermediate. This view seemed consistent with long-standing difficulty in detecting any reaction intermediates at the Q(o) site. New perspective on this issue is now offered by recent, independent reports on detection of SQ in this site. Each of the described SQs seems to have different spectroscopic properties leaving space for various interpretations and mechanistic considerations. Here, we comparatively reflect on those properties and their consequences on the SQ stabilization, the involvement of SQ in catalytic reactions, including proton transfers, and the reactivity of SQ with oxygen associated with superoxide generation activity of the Q(o) site

Mitochondrial disease-related mutation G167P in cytochrome b of Rhodobacter capsulatus cytochrome bc_{1} (S151P in human) affects the equilibrium distribution of 2Fe-2S cluster and generation of superoxide

Cytochrome bc(1) is one of the key enzymes of many bioenergetic systems. Its operation involves a large scale movement of a head domain of iron-sulfur protein (ISP-HD), which functionally connects the catalytic quinol oxidation Q(o) site in cytochrome b with cytochrome c(1). The Q(o) site under certain conditions can generate reactive oxygen species in the reaction scheme depending on the actual position of ISP-HD in respect to the Q(o) site. Here, using a bacterial system, we show that mutation G167P in cytochrome b shifts the equilibrium distribution of ISP-HD toward positions remote from the Q(o) site. This renders cytochrome bc(1) non-functional in vivo. This effect is remediated by addition of alanine insertions (1Ala and 2Ala) in the neck region of the ISP subunit. These insertions, which on their own shift the equilibrium distribution of ISP-HD in the opposite direction (i.e. toward the Q(o) site), also act in this manner in the presence of G167P. Changes in the equilibrium distribution of ISP-HD in G167P lead to an increased propensity of cytochrome bc(1) to generate superoxide, which becomes evident when the concentration of quinone increases. This result corroborates the recently proposed model in which “semireverse” electron transfer back to the Q(o) site, occurring when ISP-HD is remote from the site, favors reactive oxygen species production. G167P suggests possible molecular effects of S151P (corresponding in sequence to G167P) identified as a mitochondrial disease-related mutation in human cytochrome b. These effects may be valid for other human mutations that change the equilibrium distribution of ISP-HD in a manner similar to G167P

A short splicing isoform of HBS1L links the cytoplasmic exosome and SKI complexes in humans.

The exosome complex is a major eukaryotic exoribonuclease that requires the SKI complex for its activity in the cytoplasm. In yeast, the Ski7 protein links both complexes, whereas a functional equivalent of the Ski7 has remained unknown in the human genome.Proteomic analysis revealed that a previously uncharacterized short splicing isoform of HBS1L (HBS1LV3) is the long-sought factor linking the exosome and SKI complexes in humans. In contrast, the canonical HBS1L variant, HBS1LV1, which acts as a ribosome dissociation factor, does not associate with the exosome and instead interacts with the mRNA surveillance factor PELOTA. Interestingly, both HBS1LV1 and HBS1LV3 interact with the SKI complex and HBS1LV1 seems to antagonize SKI/exosome supercomplex formation. HBS1LV3 contains a unique C-terminal region of unknown structure, with a conserved RxxxFxxxL motif responsible for exosome binding and may interact with the exosome core subunit RRP43 in a way that resembles the association between Rrp6 RNase and Rrp43 in yeast. HBS1LV3 or the SKI complex helicase (SKI2W) depletion similarly affected the transcriptome, deregulating multiple genes. Furthermore, half-lives of representative upregulated mRNAs were increased, supporting the involvement of HBS1LV3 and SKI2W in the same mRNA degradation pathway, essential for transcriptome homeostasis in the cytoplasm

How do xanthophylls protect lipid membranes from oxidative damage?

Here, we address the problem of the antioxidant activity of carotenoids in biomembranes. The activity of lutein and zeaxanthin in the quenching of singlet oxygen generated by photosensitization was monitored in lipid vesicles using a singlet oxygen-sensitive fluorescent probe and with the application of fluorescence lifetime imaging microscopy. The antioxidant activity of xanthophylls was interpreted on the basis of electron paramagnetic resonance oximetry results showing that xanthophylls constitute a barrier to the penetration of molecular oxygen into lipid membranes: to a greater extent in the 13-cis configuration than in all-trans. These results are discussed in relation to the trans-cis photoisomerization of xanthophylls observed in the human retina. It can be concluded that photoisomerization of xanthophylls is a regulatory mechanism that is important for both the modulation of light filtration through the macula and photoprotection by quenching singlet oxygen and creating a barrier to oxygen permeation to membranes

Clinical presentation, sexual function and quality of life as predictors of sexual satisfaction among women with urinary incontinence before a vaginal revitalization procedure

Purpose: Urinary incontinence (UI) is a common condition among women that affects quality of life, depressive symptoms and sexual function. The aim of the study was to verify whether clinical data, sexual dysfunction and quality of life may be independent predictors of life satisfaction of women with UI. Methods: The study group included 76 patients who reported to a gynaecological clinic for vaginal revitalisation due to symptoms typical of UI. The patients completed: Life Satisfaction Questionnaire (FLZ), Female Sexual Function Index (FSFI), Incontinence Quality of Life Questionnaire (I-QOL) and Beck Depression Inventory (BDI). Results: The UI patients presented a lower mean score regarding satisfaction with sex than a comparable healthy population. A high score on the FLZ-sex scale was predicted by lack of labour complications, a high score on the FLZ-health and FLZ-relationships scales, and FSFI arousal scale. Conclusions: UI appears to be linked particularly strongly to low satisfaction with sex as a dimension of life satisfaction. Memory of labour complications was associated to dissatisfaction with sex. On the other hand, no link between satisfaction with sex and episiotomy, caesarean section or natural childbirth was found. High satisfaction with sex was linked to high satisfaction with general health and relationship, as well as high arousal as a sexual function

High-resolution cryo-EM structures of plant cytochrome b6fb_{6}f at work

Plants use solar energy to power cellular metabolism. The oxidation of plastoquinol and reduction of plastocyanin by cytochrome $b_{6}f$ (Cyt $b_{6}f$) is known as one of the key steps of photosynthesis, but the catalytic mechanism in the plastoquinone oxidation site ($Q_{p}$) remains elusive. Here, we describe two high-resolution cryo-EM structures of the spinach Cyt $b_{6}f$ homodimer with endogenous plastoquinones and in complex with plastocyanin. Three plastoquinones are visible and line up one after another head to tail near $Q_{p}$ in both monomers, indicating the existence of a channel in each monomer. Therefore, quinones appear to flow through Cyt $b_{6}f$ in one direction, transiently exposing the redox-active ring of quinone during catalysis. Our work proposes an unprecedented one-way traffic model that explains efficient quinol oxidation during photosynthesis and respiration. Structures of cytochrome $b_{6}f$ with and without plastocyanin imply a one-way traffic of quinones for efficient photosynthesis

The association between affective temperaments and depressive symptoms in a population of medical university students, Poland

BackgroundCompared to their peers, medical students are more exposed to stress, and many present symptoms of depression, making them a group prone to experiencing mental illnesses.ObjectiveThis study investigates a potential link between the occurrence of symptoms of depression and the dominating type of affective temperament in young people studying at a medical university.MethodsOne hundred thirty-four medical students were surveyed using two validated questionnaires; the Polish versions of Beck’s Depression Inventory-II (BDI-II) and the Temperament Evaluation of the Memphis, Pisa, and San Diego Autoquestionnaire (TEMPS-A).ResultsThe data analysis revealed a significant link between symptoms of depression and affective temperaments, most significantly in subjects with an anxious temperament.ConclusionThis study confirms the role of various affective temperaments as a risk factor for mood disorders, specifically depression

Intrinsically disordered N-terminal domain of the Helicoverpa armigera Ultraspiracle stabilizes the dimeric form via a scorpion-like structure

Nuclear receptors (NRs) are a family of ligand-dependent transcription factors activated by lipophilic compounds. NRs share a common structure comprising three domains: a variable N-terminal domain (NTD), a highly conserved globular DNA-binding domain and a ligand-binding domain. There are numerous papers describing the molecular details of the latter two globular domains. However, very little is known about the structure-function relationship of the NTD, especially as an intrinsically disordered fragment of NRs that may influence the molecular properties and, in turn, the function of globular domains. Here, we investigated whether and how an intrinsically disordered NTD consisting of 58 amino acid residues affects the functions of the globular domains of the Ultraspiracle protein from Helicoverpa armigera (HaUsp). The role of the NTD was examined for two well-known and easily testable NR functions, i.e., interactions with specific DNA sequences and dimerization. Electrophoretic mobility shift assays showed that the intrinsically disordered NTD influences the interaction of HaUsp with specific DNA sequences, apparently by destabilization of HaUsp-DNA complexes. On the other hand, multi-angle light scattering and sedimentation velocity analytical ultracentrifugation revealed that the NTD acts as a structural element that stabilizes HaUsp homodimers. Molecular models based on small-angle X-ray scattering indicate that the intrinsically disordered NTD may exert its effects on the tested HaUsp functions by forming an unexpected scorpion-like structure, in which the NTD bends towards the ligand-binding domain in each subunit of the HaUsp homodimer. This structure may be crucial for specific NTD-dependent regulation of the functions of globular domains in NR