Photoactivation of an Acid-Sensitive Ion Channel Associated with Vision and Pain

We describe the reversible photoactivation of the acid sensitive ligand-gated ion channel ASIC2a, a mammalian channel found throughout the central and peripheral nervous systems that is associated with vision and pain. We also show the activation of GLIC, an acid-sensitive prokaryotic homologue of the nicotinic acetylcholine receptor. Photoactivation was achieved by using visible light irradiation of a newly synthesized water-soluble merocyanine photoacid, 1, which was designed to remove adverse channel blocking effects of a related system. Activation of ASIC2a and GLIC occurs reversibly, in a benign manner, and only upon irradiation. Further studies using transient absorption spectroscopy showed that protonation of a colorimetric base occurred rapidly (ca. 100 μs) after excitation of 1. These results demonstrate that irradiation of 1 can induce rapid, local pH changes that can be used to investigate both biological and chemical proton transfer reactions

Mechanistic Studies of the Photoinduced Quinone Trimethyl Lock Decaging Process

Mechanistic studies of a general reaction that decages a wide range of substrates on exposure to visible light are described. The reaction involves a photochemically initiated reduction of a quinone mediated by an appended thioether. After reduction, a trimethyl lock system incorporated into the quinone leads to thermal decaging. The reaction could be viewed as an electron-transfer initiated reduction of the quinone or as a hydrogen abstraction—Norrish Type II—reaction. Product analysis, kinetic isotope effects, stereochemical labeling, radical clock, and transient absorption studies support the electron transfer mechanism. The differing reactivities of the singlet and triplet states are determined, and the ways in which this process deviates from typical quinone photochemistry are discussed. The mechanism suggests strategies for extending the reaction to longer wavelengths that would be of interest for applications in chemical biology and in a therapeutic setting

Proton-coupled electron hopping in Ru-modified P. aeruginosa azurin

We constructed two artificial multiple-step electron transfer (hopping) systems based on Pseudomonas aeruginosa azurin where a tyrosine (YOH) is situated between Ru(2,2′-bipyridine)_2(imidazole)(histidine) and the native copper site: RuH107YOH109 and RuH124-YOH122. We investigated the rates of Cu^I oxidation by flash-quench generated Ru^(III) over a range of conditions that probed the role of proton-coupled oxidation/reduction of YOH in the reaction. Rates of Cu^I oxidation were enhanced over single-step electron transfer by factors between 3 and 80, depending on specific scaffold and buffer conditions

Insights into an efficient light-driven hybrid P450 BM3 enzyme from crystallographic, spectroscopic and biochemical studies

Background: In order to perform selective C-H functionalization upon visible light irradiation, Ru(II)-diimine functionalized P450 heme enzymes have been developed. The sL407C-1 enzyme containing the Ru(bpy)_2PhenA (bpy = 2,2′-bipyridine and PhenA = 5-acetamido-1,10-phenanthroline) photosensitizer (1) covalently attached to the non-native single cysteine L407C of the P450BM3 heme domain mutant, displays high photocatalytic activity in the selective C-H bond hydroxylation of several substrates. Methods: A combination of X-ray crystallography, site-directed mutagenesis, transient absorption measurements and enzymatic assays was used to gain insights into its photocatalytic activity and electron transfer pathway. Results: The crystal structure of the sL407C-1 enzyme was solved in the open and closed conformations revealing a through-space electron transfer pathway involving highly conserved, F393 and Q403, residues. Several mutations of these residues (F393A, F393W or Q403W) were introduced to probe their roles in the overall reaction. Transient absorption measurements confirm rapid electron transfer as heme reduction is observed in all four hybrid enzymes. Compared to the parent sL407C-1, photocatalytic activity was negligible in the dF393A-1 enzyme while 60% increase in activity with total turnover numbers of 420 and 90% product conversion was observed with the dQ403W-1 mutant. Conclusions: In the sL407C-1 enzyme, the photosensitizer is ideally located to rapidly deliver electrons, using the naturally occurring electron transfer pathway, to the heme center in order to activate molecular dioxygen and sustain photocatalytic activity. General significance: The results shed light on the design of efficient light-driven biocatalysts and the approach can be generalized to other members of the P450 superfamily

Insights into an efficient light-driven hybrid P450 BM3 enzyme from crystallographic, spectroscopic and biochemical studies

Background: In order to perform selective C-H functionalization upon visible light irradiation, Ru(II)-diimine functionalized P450 heme enzymes have been developed. The sL407C-1 enzyme containing the Ru(bpy)_2PhenA (bpy = 2,2′-bipyridine and PhenA = 5-acetamido-1,10-phenanthroline) photosensitizer (1) covalently attached to the non-native single cysteine L407C of the P450BM3 heme domain mutant, displays high photocatalytic activity in the selective C-H bond hydroxylation of several substrates. Methods: A combination of X-ray crystallography, site-directed mutagenesis, transient absorption measurements and enzymatic assays was used to gain insights into its photocatalytic activity and electron transfer pathway. Results: The crystal structure of the sL407C-1 enzyme was solved in the open and closed conformations revealing a through-space electron transfer pathway involving highly conserved, F393 and Q403, residues. Several mutations of these residues (F393A, F393W or Q403W) were introduced to probe their roles in the overall reaction. Transient absorption measurements confirm rapid electron transfer as heme reduction is observed in all four hybrid enzymes. Compared to the parent sL407C-1, photocatalytic activity was negligible in the dF393A-1 enzyme while 60% increase in activity with total turnover numbers of 420 and 90% product conversion was observed with the dQ403W-1 mutant. Conclusions: In the sL407C-1 enzyme, the photosensitizer is ideally located to rapidly deliver electrons, using the naturally occurring electron transfer pathway, to the heme center in order to activate molecular dioxygen and sustain photocatalytic activity. General significance: The results shed light on the design of efficient light-driven biocatalysts and the approach can be generalized to other members of the P450 superfamily

Visible-Light-Induced Olefin Activation Using 3D Aromatic Boron-Rich Cluster Photooxidants

We report a discovery that perfunctionalized icosahedral dodecaborate clusters of the type B_(12)(OCH_2Ar)_(12) (Ar = Ph or C_6F_5) can undergo photo-excitation with visible light, leading to a new class of metal-free photooxidants. Excitation in these species occurs as a result of the charge transfer between low-lying orbitals located on the benzyl substituents and an unoccupied orbital delocalized throughout the boron cluster core. Here we show how these species, photo-excited with a benchtop blue LED source, can exhibit excited-state reduction potentials as high as 3 V and can participate in electron-transfer processes with a broad range of styrene monomers, initiating their polymerization. Initiation is observed in cases of both electron-rich and electron-deficient styrene monomers at cluster loadings as low as 0.005 mol%. Furthermore, photo-excitation of B_(12)(OCH_2C_6F_5)_(12) in the presence of a less activated olefin such as isobutylene results in the production of highly branched poly(isobutylene). This work introduces a new class of air-stable, metal-free photo-redox reagents capable of mediating chemical transformations

Global burden of 369 diseases and injuries in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study 2019

Background: In an era of shifting global agendas and expanded emphasis on non-communicable diseases and injuries along with communicable diseases, sound evidence on trends by cause at the national level is essential. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) provides a systematic scientific assessment of published, publicly available, and contributed data on incidence, prevalence, and mortality for a mutually exclusive and collectively exhaustive list of diseases and injuries. Methods: GBD estimates incidence, prevalence, mortality, years of life lost (YLLs), years lived with disability (YLDs), and disability-adjusted life-years (DALYs) due to 369 diseases and injuries, for two sexes, and for 204 countries and territories. Input data were extracted from censuses, household surveys, civil registration and vital statistics, disease registries, health service use, air pollution monitors, satellite imaging, disease notifications, and other sources. Cause-specific death rates and cause fractions were calculated using the Cause of Death Ensemble model and spatiotemporal Gaussian process regression. Cause-specific deaths were adjusted to match the total all-cause deaths calculated as part of the GBD population, fertility, and mortality estimates. Deaths were multiplied by standard life expectancy at each age to calculate YLLs. A Bayesian meta-regression modelling tool, DisMod-MR 2.1, was used to ensure consistency between incidence, prevalence, remission, excess mortality, and cause-specific mortality for most causes. Prevalence estimates were multiplied by disability weights for mutually exclusive sequelae of diseases and injuries to calculate YLDs. We considered results in the context of the Socio-demographic Index (SDI), a composite indicator of income per capita, years of schooling, and fertility rate in females younger than 25 years. Uncertainty intervals (UIs) were generated for every metric using the 25th and 975th ordered 1000 draw values of the posterior distribution. Findings: Global health has steadily improved over the past 30 years as measured by age-standardised DALY rates. After taking into account population growth and ageing, the absolute number of DALYs has remained stable. Since 2010, the pace of decline in global age-standardised DALY rates has accelerated in age groups younger than 50 years compared with the 1990–2010 time period, with the greatest annualised rate of decline occurring in the 0–9-year age group. Six infectious diseases were among the top ten causes of DALYs in children younger than 10 years in 2019: lower respiratory infections (ranked second), diarrhoeal diseases (third), malaria (fifth), meningitis (sixth), whooping cough (ninth), and sexually transmitted infections (which, in this age group, is fully accounted for by congenital syphilis; ranked tenth). In adolescents aged 10–24 years, three injury causes were among the top causes of DALYs: road injuries (ranked first), self-harm (third), and interpersonal violence (fifth). Five of the causes that were in the top ten for ages 10–24 years were also in the top ten in the 25–49-year age group: road injuries (ranked first), HIV/AIDS (second), low back pain (fourth), headache disorders (fifth), and depressive disorders (sixth). In 2019, ischaemic heart disease and stroke were the top-ranked causes of DALYs in both the 50–74-year and 75-years-and-older age groups. Since 1990, there has been a marked shift towards a greater proportion of burden due to YLDs from non-communicable diseases and injuries. In 2019, there were 11 countries where non-communicable disease and injury YLDs constituted more than half of all disease burden. Decreases in age-standardised DALY rates have accelerated over the past decade in countries at the lower end of the SDI range, while improvements have started to stagnate or even reverse in countries with higher SDI. Interpretation: As disability becomes an increasingly large component of disease burden and a larger component of health expenditure, greater research and developm nt investment is needed to identify new, more effective intervention strategies. With a rapidly ageing global population, the demands on health services to deal with disabling outcomes, which increase with age, will require policy makers to anticipate these changes. The mix of universal and more geographically specific influences on health reinforces the need for regular reporting on population health in detail and by underlying cause to help decision makers to identify success stories of disease control to emulate, as well as opportunities to improve. Funding: Bill & Melinda Gates Foundation. © 2020 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licens