Kinetic Aspects of the Interaction between Ligand and G Protein-Coupled Receptor: The Case of the Adenosine Receptors

Ligand–receptor binding kinetics is an emerging topic in the drug research community. Over the past years, medicinal chemistry approaches from a kinetic perspective have been increasingly applied to G protein-coupled receptors including the adenosine receptors (AR), which are involved in a plethora of physiological and pathological conditions. The study of ligand–AR binding kinetics offers room for detailed structure–kinetics relationships next to more traditional structure–activity relationships. Their combination may facilitate the triage of candidate compounds in hit-to-lead campaigns. Furthermore, kinetic studies also help in understanding AR allosterism. Allosteric modulation may yield a change in the activity and conformation of a receptor resulting from the binding of a compound at a site distinct from where the endogenous agonist adenosine binds. Hence, in this Review, we summarize available data and evidence for the binding kinetics of orthosteric and allosteric AR ligands. We hope this Review will raise awareness to consider the kinetic aspects of drug–target interactions on both ARs and other drug targets.Medicinal Chemistr

Field Measurement of Soil Surface Chemical Transport Properties for Comparison of Management Zones

Management of chemicals in soil is important, yet the complexity of field soils limits prediction of management effects on transport. To date, few methods have been available for field measurement of chemical transport properties, but a recently developed dripper–time domain reflectometry technique allows rapid collection of data for determining these properties. The objective of this work was to apply this technique for comparison of chemical transport properties for different soil management zones. Experiments were conducted comparing four interrow management zones: no-till nontrafficked, no-till trafficked, chisel plow nontrafficked, and chisel plow trafficked. Drip emitters were positioned at 12 locations in each zone and used to apply water followed by a step input of CaCl2 tracer solution. Breakthrough curves were measured via electrical conductivity with time domain reflectometry probes. The mobile–immobile model was fit to the breakthrough curves to determine chemical transport properties. Mean chemical transport properties were 0.34, 0.11 h−1, 10 cm h−1, 164 cm2 h−1, and 5 cm, for the immobile water fraction, mass exchange coefficient, average pore-water velocity, mobile dispersion coefficient, and dispersivity, respectively. All five properties showed significant differences between management zones. Differences in mass exchange and mobile dispersion coefficients coincided with differences in tillage, while differences in mean pore water velocities coincided with differences in traffic. The immobile water fraction was largest for the no-till nontrafficked zone. These results represent one of very few reports for field measurement of chemical transport properties and the first application of this approach for comparison of chemical transport properties across management zones

Soil water retention and hydraulic conductivity dynamics following tillage

Soil bulk density (ρb) may be purposely reduced in agricultural fields using tillage to improve hydraulic properties. However, tillage alters the soil structure, resulting in unstable soils. As the soil stabilizes, ρb increases over time. While this is known, studies on soil hydraulic properties in tilled soils, including comparisons between tilled and non-tilled soils, commonly assume a rigid soil structure. This study presents changes in soil water retention and saturated hydraulic conductivity (Ksat) as ρb increased dynamically with time following tillage at a loam-textured field site. Over the summer of 2015, soil cores were collected at several depths below the surface following precipitation events. Soil water retention curves and Ksat were determined using pressure cells and the constant head method, respectively. Tillage reduced ρb to 0.94 g cm−3. Changes in ρb increased with depth, reaching a ρb of 1.11 g cm−3 in the 0–5 cm layer, and a ρb of 1.42 g cm−3 at the deepest tilled layer. Soil water retention curves were markedly steeper for samples with higher ρb, indicating an overall increase in water retained at a soil matric potential (Ψ) of −33 kPa. Evaluation of two modeling approaches for water retention as a function ρbindicated that changes in water retention with increases in ρb could be reasonably estimated if a matching point was used. No clear relationship between Ksat and ρbwas obvious for ρb \u3c 1.06 cm3 cm−3, but for ρb \u3e 1.06 cm3 cm−3, Ksat decreased markedly (order of magnitude) as ρb increased. Hydraulic properties varied strongly depending on time since tillage and soil depth, and results have implications for models of tilled soils, as well as for studies comparing tilled and non-tilled soils

Turbidimetric Determination of Anionic Polyacrylamide in Low Carbon Soil Extracts

Concerns over runoff water quality from agricultural lands and construction sites have led to the development of improved erosion control practices, including application of polyacrylamide (PAM). We developed a quick and reliable method for quantifying PAM in soil extracts at low carbon content by using a turbidimetric reagent, Hyamine 1622. Three high-molecular weight anionic PAMs differing in charge density (7, 20, and 50 mol%) and five water matrices, deionized (DI) water and extracts from four different soils, were used to construct PAM calibration curves by reacting PAM solutions with hyamine and measuring turbidity development from the PAM–hyamine complex. The PAM calibration curve with DI water showed a strong linear relationship (r2 = 0.99), and the sensitivity (slope) of calibration curves increased with increasing PAM charge density with a detection limit of 0.4 to 0.9 mg L−1. Identical tests with soil extracts showed the sensitivity of the hyamine method was dependent on the properties of the soil extract, primarily organic carbon concentration. Although the method was effective in mineral soils, the highest charge density PAM yielded a more reliable linear relationship (r2 \u3e 0.97) and lowest detection limit (0.3 to 1.2 mg L−1), compared with those of the lower charge density PAMs (0.7 to 23 mg L−1). Our results suggest that the hyamine test could be an efficient method for quantifying PAM in environmental soil water samples as long as the organic carbon in the sample is low, such as in subsurface soil material often exposed at construction sites

Evaluation of a new, perforated heat flux plate design

Accurate measurement of heat flux is essential to optimize structural and process design and to improve understanding of energy transfer in natural systems. Laboratory and field experiments evaluated the performance of a new, perforated heat flux plate designed to reduce flow distortion for environmental applications. Laboratory tests involving dry and saturated sand showed that performance of the new CAPTEC plate is comparable to a solid, standard REBS plate. Very low thermal gradients may have however led to poor performance of the CAPTEC plate in saturated sand. Water infiltration and redistribution experiments using clayey and sandy soils showed an apparent reduced disruption of liquid water and vapour in the soil surrounding the CAPTEC plate as compared to solid Hukseflux and standard REBS plates. Surface area of REBS plate, though smaller than that of CAPTEC, did not lead to any significantly improved evaporation, due to perforations on CAPTEC plate. Field tests in a loam soil indicated that the CAPTEC plates were durable and produced daily total flux values within ~ 0.15 MJ m− 2 of independent estimates

Fragment screening of GPCRs using biophysical methods: identification of ligands of the adenosine A(2A) receptor with novel biological activity

Medicinal Chemistr

The Viscoelastic Properties of the Fungal Cell Wall Allow Traffic of AmBisome as Intact Liposome Vesicles

NARG thanks The Wellcome Trust (080088, 086827, 075470, 099215 & 097377) and MRC Centre for Medical Mycology (MR/N006364/1) and acknowledges financial support from Gilead Sciences for a studentship and grant IX-EU-131-0262. Dr. Linda Soo Hoo and Tark Bunch of Gilead provided expert technical assistance in liposomal sample preparations and GF provided gold labelled test articles. JAM is funded in part from a research grant from Gilead Sciences Inc. ML was supported by the MRC (MR/J008230/1). AC was supported in part by 5R01HL059842, 5R01AI033774, 5R37AI033142, and 5R01AI052733. We thank Debbie Wilkinson and Kevin McKenzie at the Imaging Core Facility at the University of Aberdeen for expert assistance with TEM.Peer reviewedPublisher PD

Design and pharmacological profile of a novel covalent partial agonist for the adenosine A1 receptor

Partial agonists for G protein-coupled receptors (GPCRs) provide opportunities for novel pharmacotherapies with enhanced on-target safety compared to full agonists. For the human adenosine A1 receptor (hA1AR) this has led to the discovery of capadenoson, which has been in phase IIa clinical trials for heart failure. Accordingly, the design and profiling of novel hA1AR partial agonists has become an important research focus. In this study, we report on LUF7746, a capadenoson derivative bearing an electrophilic fluorosulfonyl moiety, as an irreversibly binding hA1AR modulator. Meanwhile, a nonreactive ligand bearing a methylsulfonyl moiety, LUF7747, was designed as a control probe in our study.In a radioligand binding assay, LUF7746’s apparent affinity increased to nanomolar range with longer pre-incubation time, suggesting an increasing level of covalent binding over time. Moreover, compared to the reference full agonist CPA, LUF7746 was a partial agonist in a hA1AR-mediated G protein activation assay and resistant to blockade with an antagonist/inverse agonist. An in silico structure-based docking study combined with site-directed mutagenesis of the hA1AR demonstrated that amino acid Y2717.36 was the primary anchor point for the covalent interaction. Additionally, a label-free whole-cell assay was set up to identify LUF7746’s irreversible activation of an A1 receptor-mediated cell morphological response.These results led us to conclude that LUF7746 is a novel covalent hA1AR partial agonist and a valuable chemical probe for further mapping the receptor activation process. It may also serve as a prototype for a therapeutic approach in which a covalent partial agonist may cause less on-target side effects, conferring enhanced safety compared to a full agonist.Toxicolog

Threats posed by the fungal kingdom to humans, wildlife, and agriculture

The fungal kingdom includes at least 6 million eukaryotic species and is remarkable with respect to its profound impact on global health, biodiversity, ecology, agriculture, manufacturing, and biomedical research. Approximately 625 fungal species have been reported to infect vertebrates, 200 of which can be human associated, either as commensals and members of our microbiome or as pathogens that cause infectious diseases. These organisms pose a growing threat to human health with the global increase in the incidence of invasive fungal infections, prevalence of fungal allergy, and the evolution of fungal pathogens resistant to some or all current classes of antifungals. More broadly, there has been an unprecedented and worldwide emergence of fungal pathogens affecting animal and plant biodiversity. Approximately 8,000 species of fungi and Oomycetes are associated with plant disease. Indeed, across agriculture, such fungal diseases of plants include new devastating epidemics of trees and jeopardize food security worldwide by causing epidemics in staple and commodity crops that feed billions. Further, ingestion of mycotoxins contributes to ill health and causes cancer. Coordinated international research efforts, enhanced technology translation, and greater policy outreach by scientists are needed to more fully understand the biology and drivers that underlie the emergence of fungal diseases and to mitigate against their impacts. Here, we focus on poignant examples of emerging fungal threats in each of three areas: human health, wildlife biodiversity, and food security