Fusing two cytochromes b of Rhodobacter capsulatus cytochrome bc1 using various linkers defines a set of protein templates for asymmetric mutagenesis

Cytochrome bc1 (mitochondrial complex III), one of the key enzymes of biological energy conversion, is a functional homodimer in which each monomer contains three catalytic subunits: cytochrome c1, the iron–sulfur subunit and cytochrome b. The latter is composed of eight transmembrane α-helices which, in duplicate, form a hydrophobic core of a dimer. We show that two cytochromes b can be fused into one 16-helical subunit using a number of different peptide linkers that vary in length but all connect the C-terminus of one cytochrome with the N-terminus of the other. The fusion proteins replace two cytochromes b in the dimer defining a set of available protein templates for introducing mutations that allow breaking symmetry of a dimer. A more detailed comparison of the form with the shortest, 3 amino acid, linker to the form with 12 amino acid linker established that both forms display similar level of structural plasticity to accommodate several, but not all, asymmetric patterns of mutations that knock out individual segments of cofactor chains. While the system based on a fused gene does not allow for the assessments of the functionality of electron-transfer paths in vivo, the family of proteins with fused cytochrome b offers attractive model for detailed investigations of molecular mechanism of catalysis at in vitro/reconstitution level

Catalytically-relevant electron transfer between two hemes b_{L} in the hybrid cytochrome bc_{1}-like complex containing a fusion of Rhodobacter sphaeroides and capsulatus cytochromes b

AbstractTo address mechanistic questions about the functioning of dimeric cytochrome bc1 new genetic approaches have recently been developed. They were specifically designed to enable construction of asymmetrically-mutated variants suitable for functional studies. One approach exploited a fusion of two cytochromes b that replaced the separate subunits in the dimer. The fusion protein, built from two copies of the same cytochrome b of purple bacterium Rhodobacter capsulatus, served as a template to create a series of asymmetrically-mutated cytochrome bc1-like complexes (B–B) which, through kinetic studies, disclosed several important principles of dimer engineering. Here, we report on construction of another fusion protein complex that adds a new tool to investigate dimeric function of the enzyme through the asymmetrically mutated forms of the protein. This complex (BS–B) contains a hybrid protein that combines two different cytochromes b: one coming from R. capsulatus and the other — from a closely related species, R. sphaeroides. With this new fusion we addressed a still controversial issue of electron transfer between the two hemes bL in the core of dimer. Kinetic data obtained with a series of BS–B variants provided new evidence confirming the previously reported observations that electron transfer between those two hemes occurs on a millisecond timescale, thus is a catalytically-relevant event. Both types of the fusion complexes (B–B and BS–B) consistently implicate that the heme-bL–bL bridge forms an electronic connection available for inter-monomer electron transfer in cytochrome bc1

Exhaled nitric oxide in patients with esophagitis

Wstęp: Ocena stężenia tlenku azotu (NO) w wydychanym powietrzu służy do monitorowania u chorych na astmę procesu zapalnego występującego w oskrzelach (FeNO). Wysokie stężenia tlenku azotu są stwierdzane również w obrębie zatok i w przewodzie pokarmowym. Prawidłowo funkcjonujące zwieracze przełyku mają zabezpieczać przed tlenkiem azotu pochodzącym z przewodu pokarmowego. Do tej pory nie było wiadomo, jaki wpływ na pomiar FeNO mają schorzenia przewodu pokarmowego, a szczególnie zaburzenia motoryki przełyku. Celem badania było wykazanie, czy choroby żołądka, a zwłaszcza przełyku, są w stanie w sposób istotny wpłynąć na stężenie tlenku azotu w wydychanym powietrzu u osób, u których nie występują schorzenia układu oddechowego. Materiał i metody: Gastroskopię z pobraniem wycinka z przełyku i żołądka wykonano u 51 pacjentów, u których wykluczono astmę, nieżyt nosa oraz atopię. U 13 z nich nie stwierdzono nieprawidłowości w obrębie przełyku. Chorzy ci stanowili grupę kontrolną. U pozostałych 38 badanych nasilenie stanu zapalnego przełyku było oceniane według skali Los Angeles. Wyniki: Stężenie tlenku azotu w wydychanym powietrzu w grupie chorych ze zmianami zapalnymi przełyku (p = 0,68), jak również żołądka nie różniło się istotnie od stężenia NO w grupie chorych bez zmian zapalnych. Również obecność przepukliny przełykowej nie wpływała istotnie statystycznie na stężenie FeNO (p = 0,67). Nie stwierdzono także istotnie statystycznej zależności stężenia NO w wydychanym powietrzu od infekcji bakterią Helicobacter pylori (p = 0,18). Wnioski: Patologie w zakresie żołądka i przełyku nie wpływają w istotny sposób na stężenie tlenku azotu w wydychanym powietrzu. Pneumonol. Alergol. Pol. 2011; 79, 4: 272–277Introduction: Assessment of nitric oxide (NO) concentration in exhaled air is broadly used to monitor the airway inflammation in asthma. High level of NO are also observed in paranasal sinuses and gastrointestinal tract (GT). The intact esopahageal sphincters are responsible for maintain the NO within the GT. It is not known how much the GT and especially esophageal motility disorders can affect the FeNO measurements. The aim of the study was to asses if the gastroesophageal reflux disease has any impact on level of NO in exhaled air in patients who do not suffer from any airway disease. Material and methods: In 51 patients, in whom asthma, nasal polyps or atopy were excluded, gastroscopy with biopsy was performed. In 13 of them no esophageal pathology was found and they were considered as the control group. In the other 38 patients the esophagitis was diagnosed based on Los Angeles classification. Results: The concentration of NO in exhaled air in patients with endoscopical gastro-esophageal changes did not differ significantly from the NO concentration in patients without inflammatory changes in stomach and esophagus (p = 0.68). Moreover, the presence of hiatal hernia did not affect the FeNO (p = 0.67). There was also no significant dependence between NO level and infection with Helicobacter pylori (p = 0.18). Conclusions: The gastroesophageal pathologies did not significantly affect NO concentration in exhaled air. Pneumonol. Alergol. Pol. 2011; 79, 4: 272–27

Enzymatic Activities of Isolated Cytochrome bc1-like Complexes Containing Fused Cytochrome b Subunits with Asymmetrically Inactivated Segments of Electron Transfer Chains

Homodimeric structure of cytochrome bc_1, a common component of biological energy conversion systems, builds in four catalytic quinone oxidation/reduction sites and four chains of cofactors (branches) that, connected by a centrally located bridge, form a symmetric H-shaped electron transfer system. The mechanism of operation of this complex system is under constant debate. Here, we report on isolation and enzymatic examination of cytochrome bc1-like complexes containing fused cytochrome b subunits in which asymmetrically introduced mutations inactivated individual branches in various combinations. The structural asymmetry of those forms was confirmed spectroscopically. All the asymmetric forms corresponding to cytochrome bc_1 with partial or full inactivation of one monomer retain high enzymatic activity but at the same time show a decrease in the maximum turnover rate by a factor close to 2. This strongly supports the model assuming independent operation of monomers. The cross-inactivated form corresponding to cytochrome bc_1 with disabled complementary parts of each monomer retains the enzymatic activity at the level that, for the first time on isolated from membranes and purified to homogeneity preparations, demonstrates that intermonomer electron transfer through the bridge effectively sustains the enzymatic turnover. The results fully support the concept that electrons freely distribute between the four catalytic sites of a dimer and that any path connecting the catalytic sites on the opposite sides of the membrane is enzymatically competent. The possibility to examine enzymatic properties of isolated forms of asymmetric complexes constructed using the cytochrome b fusion system extends the array of tools available for investigating the engineering of dimeric cytochrome bc1 from the mechanistic and physiological perspectives

Is (poly-) substance use associated with impaired inhibitory control? A mega-analysis controlling for confounders.

Many studies have reported that heavy substance use is associated with impaired response inhibition. Studies typically focused on associations with a single substance, while polysubstance use is common. Further, most studies compared heavy users with light/non-users, though substance use occurs along a continuum. The current mega-analysis accounted for these issues by aggregating individual data from 43 studies (3610 adult participants) that used the Go/No-Go (GNG) or Stop-signal task (SST) to assess inhibition among mostly "recreational" substance users (i.e., the rate of substance use disorders was low). Main and interaction effects of substance use, demographics, and task-characteristics were entered in a linear mixed model. Contrary to many studies and reviews in the field, we found that only lifetime cannabis use was associated with impaired response inhibition in the SST. An interaction effect was also observed: the relationship between tobacco use and response inhibition (in the SST) differed between cannabis users and non-users, with a negative association between tobacco use and inhibition in the cannabis non-users. In addition, participants' age, education level, and some task characteristics influenced inhibition outcomes. Overall, we found limited support for impaired inhibition among substance users when controlling for demographics and task-characteristics

Tripodal Podand Ligand with a Superhalogen Nature as an Effective Molecular Trap

Tris(2-methoxyethyl) fluoroborate anion (TMEFA), anovel tripodal ligand based on the BF4− superhalogen anion, is proposed and was investigated theoretically using ab initio MP2 (second-order Møller-Plesset perturbational method) and OVGF (outer valence Green function) methods. The studied molecule comprises three 2-methoxyethoxy groups (-O-CH2-CH2-O-CH3) connected to a central boron atom, which results in the C3-symmetry of the compound. The resulting anion was stable against fragmentation processes and its vertical electron detachment energy was found to be 5.72 eV. Due to its equilibrium structure resembling that of classical tripodal podands, the [F-B(O-CH2-CH2-O-CH3)3]− anion is capable of binding metal cations using its three arms, and thus may form strongly bound ionic complexes such as [F-B(O-CH2-CH2-O-CH3)3]−/Li+ and [F-B(O-CH2-CH2-O-CH3)3]−/Mg2+. The binding energies predicted for such compounds far exceed those of the similar neutral classical podand ligands, which likely makes the [F-B(O-CH2-CH2-O-CH3)3]− system a more effective molecular trap or steric shielding agent with respect to selected metal cations