The movement of protons and electrons is common to the synthesis of all chemical fuels such as H2. Hydrogenases, which catalyze the reversible reduction of protons, necessitate transport and reactivity between protons and electrons, but a detailed mechanism has thus far been elusive. Here, we use a phototriggered chemical potential jump method to rapidly initiate the proton reduction activity of a [NiFe] hydrogenase. Coupling the photochemical initiation approach to nanosecond transient infrared and visible absorbance spectroscopy afforded direct observation of interfacial electron transfer and active site chemistry. Tuning of intramolecular proton transport by pH and isotopic substitution revealed distinct concerted and stepwise proton-coupled electron transfer mechanisms in catalysis. The observed heterogeneity in the two sequential proton-associated reduction processes suggests a highly engineered protein environment modulating catalysis and implicates three new reaction intermediates; Nia-I, Nia-D, and Nia-SR(-). The results establish an elementary mechanistic understanding of catalysis in a [NiFe] hydrogenase with implications in enzymatic proton-coupled electron transfer and biomimetic catalyst design.

Hydrogen gas-evolving membrane-bound hydrogenase (MBH) and quinone-reducing complex I are homologous respiratory complexes with a common ancestor, but a structural basis for their evolutionary relationship is lacking. Here, we report the cryo-EM structure of a 14-subunit MBH from the hyperthermophile Pyrococcus furiosus. MBH contains a membrane-anchored hydrogenase module that is highly similar structurally to the quinone-binding Q-module of complex I while its membrane-embedded ion-translocation module can be divided into a H- and a Na-translocating unit. The H-translocating unit is rotated 180° in-membrane with respect to its counterpart in complex I, leading to distinctive architectures for the two respiratory systems despite their largely conserved proton-pumping mechanisms. The Na-translocating unit, absent in complex I, resembles that found in the Mrp H/Na antiporter and enables hydrogen gas evolution by MBH to establish a Na gradient for ATP synthesis near 100°C. MBH also provides insights into Mrp structure and evolution of MBH-based respiratory enzymes.

Background The COVID-19 pandemic posed a huge challenge to the education systems worldwide, forcing many countries to provisionally close educational institutions and deliver courses fully online. The aim of this study was to explore the quality of the online education in China for international medical and nursing students from low- and middle-income countries (LMICs) as well as the factors that influenced their satisfaction with online education during the COVID-19 pandemic. Methods Questionnaires were developed and administered to 316 international medical and nursing students and 120 teachers at a university in China. The Chi-square test was used to detect the influence of participants’ personal characteristics on their satisfaction with online education. The Kruskal–Wallis rank-sum test was employed to identify the negative and positive factors influencing the online education satisfaction. A binary logistic regression model was performed for multiple-factor analysis to determine the association of the different categories of influential factors—crisis-, learner-, instructor-, and course-related categories, with the online education satisfaction. Results Overall, 230 students (response rate 72.8%) and 95 teachers (response rate 79.2%) completed the survey. It was found that 36.5% of students and 61.1% of teachers were satisfied with the online education. Teachers’ professional title, students’ year of study, continent of origin and location of current residence significantly influenced the online education satisfaction. The most influential barrier for students was the severity of the COVID-19 situation and for teachers it was the sense of distance. The most influential facilitating factor for students was a well-accomplished course assignment and for teachers it was the successful administration of the online courses. Conclusions Several key factors have been identified that affected the attitudes of international health science students from LMICs and their teachers towards online education in China during the COVID-19 pandemic. To improve the online education outcome, medical schools are advised to promote the facilitating factors and cope with the barriers, by providing support for students and teaching faculties to deal with the anxiety caused by the pandemic, caring for the state of mind of in-China students away from home, maintaining the engagement of out-China students studying from afar and enhancing collaborations with overseas institutions to create practice opportunities at students’ local places.

Hydrogenases (H2ases) represent one of the most striking examples of biological proton-coupled electron transfer (PCET) chemistry, functioning in facile proton reduction and H2 oxidation involving long-range proton and electron transport. Spectroscopic and electrochemical studies of the [NiFe] H2ases have identified several catalytic intermediates, but the details of their interconversion are still a matter of debate. Here we use steady state and time-resolved infrared spectroscopy, sensitive to the CO ligand of the active site iron, as a probe of the proton inventory as well as electron and proton transfer dynamics in the soluble hydrogenase I from Pyrococcus furiosus. Subtle shifts in infrared signatures associated with the Nia-C and Nia-S states as a function of pH revealed an acid-base equilibrium associated with an ionizable amino acid near the active site. Protonation of this residue was found to correlate with the photoproduct distribution that results from hydride photolysis of the Nia-C state, in which one of the two photoproduct states becomes inaccessible at low pH. Additionally, the ability to generate Nia-S via PCET from Nia-C was weakened at low pH, suggesting prior protonation of the proton acceptor. Kinetic and thermodynamic analysis of electron and proton transfer with respect to the various proton inventories was utilized to develop a chemical model for reversible hydride oxidation involving two intermediates differing in their hydrogen bonding character.

The Ca 2+ -regulating and electrophysiological properties of guinea-pig suburothelial myofibroblasts have been measured in order to investigate their potential role in the sensation of bladder fullness, due to their strategic position between the urothelium and afferent fibres. Previous work has shown that stretch of the bladder wall releases ATP. Cells that stain positively for vimentin were isolated. About 45% of cells (median membrane capacitance 13.3 pF) exhibited spontaneous depolarizations to about −25 mV with a physiological Cl − gradient (frequency 2.6 ± 1.5 min −1 , duration 14.5 ± 2.2 s, n = 15). Under voltage-clamp spontaneous inward currents (frequency 1.5 ± 0.2 min −1 , duration 14.5 ± 7.0 s, n = 18) were recorded, with a similar reversal potential. The spontaneous currents were preceded by intracellular Ca 2+ transients with a magnitude that was independent of membrane potential. All cells tested responded to ATP by generating an intracellular Ca 2+ transient, followed by inward currents; the currents had a similar reversal potential and slope conductance to their spontaneous counterparts. ATP-generated transients were mimicked by UTP and ADP but not by α,β-methylene-ATP (1-10 µM) or CTP (30 µM), indicating that ATP acts via a P2Y receptor. Transients were partially attenuated by 1 mM suramin but PPADS (80 µM) had no effect. These data indicate that ATP acts via a P2Y receptor, but responses were resistant to the P2Y 1 antagonist MRS2179. ATP-generated transients were abolished by intracellular perfusion with heparin and TMB-8 indicating that IP 3 was the intracellular second messenger. The reversal potentials of the spontaneous and ATP-generated currents were shifted by about +45 mV by a 12-fold reduction of the extracellular [Cl − ] and the currents were greatly attenuated by 1 mM DIDS. No transients were generated on exposure to the muscarinic agonist carbachol. We propose that these cells may play a regulatory step in the sensation of bladder fullness by responding to ATP. The precise mechanism whereby they couple urothelial ATP release to afferent excitation is the next step to be elucidated.