An Investigation of the Catalytic Mechanism of S-adenosylmethionine Synthetase by QM/MM Calculations

Catalysis by S-adenosylmethionine synthetase has been investigated by quantum mechanical/molecular mechanical calculations, exploiting structures of the active crystalline enzyme. The transition state energy of +19.1 kcal/mol computed for a nucleophilic attack of the methionyl sulfur on carbon-5′ of the nucleotide was indistinguishable from the experimental (solution) value when the QM residues were an uncharged histidine that hydrogen bonds to the leaving oxygen-5′ and an aspartate that chelates a Mg2+ ion, and was similar (+18.8 kcal/mol) when the QM region also included the active site arginine and lysines. The computed energy difference between reactant and product was also consistent with their equimolar abundance in co-crystals. The calculated geometrical changes support catalysis of a SN2 reaction through hydrogen bonding of the liberated oxygen-5′ to the histidine, charge neutralization by the 2 Mg2+ ions, and stabilization of the product sulfonium cation through a close, non-bonded, contact between the sulfur and the ribose 4′-oxygen

Shape Shifting Leads to Small-Molecule Allosteric Drug Discovery

SummaryEnzymes that regulate their activity by modulating an equilibrium of alternate, nonadditive, functionally distinct oligomeric assemblies (morpheeins) constitute a recently described mode of allostery. The oligomeric equilibrium for porphobilinogen synthase (PBGS) consists of high-activity octamers, low-activity hexamers, and two dimer conformations. A phylogenetically diverse allosteric site specific to hexamers is proposed as an inhibitor binding site. Inhibitor binding is predicted to draw the oligomeric equilibrium toward the low-activity hexamer. In silico docking enriched a selection from a small-molecule library for compounds predicted to bind to this allosteric site. In vitro testing of selected compounds identified one compound whose inhibition mechanism is species-specific conversion of PBGS octamers to hexamers. We propose that this strategy for inhibitor discovery can be applied to other proteins that use the morpheein model for allosteric regulation

Rationale, design and study protocol of the ‘Strong Families Start at Home’ feasibility trial to improve the diet quality of low-income, ethnically diverse children by helping parents improve their feeding and food preparation practices

There is an urgent need to create effective interventions that help parents establish a healthy diet among their children early in life, especially among low-income and ethnically and racially diverse families. U.S. children eat too few fruits, vegetables and whole grains, and too many energy dense foods, dietary behaviors associated with increased morbidity from chronic diseases. Parents play a key role in shaping children\u27s diets. Best practices suggest that parents should involve children in food preparation, and offer, encourage and model eating a variety of healthy foods. In addition, while parents help to shape food preferences, not all children respond in the same way. Certain child appetitive traits, such as satiety responsiveness (sensitivity to internal satiety signals), food responsiveness (sensitivity to external food cues), and food fussiness may help explain some of these differences. Prior interventions to improve the diet of preschool children have not used a holistic approach that targets the home food environment, by focusing on food quality, food preparation, and positive feeding practices while also acknowledging a child\u27s appetitive traits. This manuscript describes the rationale and design for a 6-month pilot randomized controlled trial, Strong Families Start at Home, that randomizes parents and their 2-to 5-year old children to either a home-based environmental dietary intervention or an attention-control group. The primary aim of the study is to explore the feasibility and acceptability of the intervention and evaluation and to determine the intervention\u27s preliminary efficacy on child diet quality, feeding practices, and availability of healthy foods in the home

Opening up the Quantum Three-Box Problem with Undetectable Measurements

One of the most striking features of quantum mechanics is the profound effect exerted by measurements alone. Sophisticated quantum control is now available in several experimental systems, exposing discrepancies between quantum and classical mechanics whenever measurement induces disturbance of the interrogated system. In practice, such discrepancies may frequently be explained as the back-action required by quantum mechanics adding quantum noise to a classical signal. Here we implement the 'three-box' quantum game of Aharonov and Vaidman in which quantum measurements add no detectable noise to a classical signal, by utilising state-of-the-art control and measurement of the nitrogen vacancy centre in diamond. Quantum and classical mechanics then make contradictory predictions for the same experimental procedure, however classical observers cannot invoke measurement-induced disturbance to explain this discrepancy. We quantify the residual disturbance of our measurements and obtain data that rule out any classical model by > 7.8 standard deviations, allowing us for the first time to exclude the property of macroscopic state-definiteness from our system. Our experiment is then equivalent to a Kochen-Spekker test of quantum non-contextuality that successfully addresses the measurement detectability loophole

Work-Unit Absenteeism: Effects of Satisfaction, Commitment, Labor Market Conditions, and Time

Prior research is limited in explaining absenteeism at the unit level and over time. We developed and tested a model of unit-level absenteeism using five waves of data collected over six years from 115 work units in a large state agency. Unit-level job satisfaction, organizational commitment, and local unemployment were modeled as time-varying predictors of absenteeism. Shared satisfaction and commitment interacted in predicting absenteeism but were not related to the rate of change in absenteeism over time. Unit-level satisfaction and commitment were more strongly related to absenteeism when units were located in areas with plentiful job alternatives

Does the Type of Chronic Heart Failure Impact In-Hospital Outcomes for Aortic Valve Replacement Procedures?

BACKGROUND: This study assessed in-hospital outcomes of patients with chronic systolic, diastolic, or mixed heart failure (HF) undergoing transcatheter aortic valve replacement (TAVR) or surgical aortic valve replacement (SAVR). METHODS: The Nationwide Inpatient Sample database was used to identify patients with aortic stenosis and chronic HF who underwent TAVR or SAVR between 2012 and 2015. Propensity score matching and multivariate logistic regression were used to determine outcome risk. RESULTS: A cohort of 9,879 patients with systolic (27.2%), diastolic (52.2%), and mixed (20.6%) chronic HF were included. No statistically significant differences in hospital mortality were noted. Overall, patients with diastolic HF had the shortest hospital stays and lowest costs. Compared with patients with diastolic HF, the risk of acute myocardial infarction (TAVR odds ratio [OR], 1.95; 95% CI, 1.20-3.19; P = .008; SAVR OR, 1.38; 95% CI, 0.98-1.95; P = .067) and cardiogenic shock (TAVR OR, 2.15; 95% CI, 1.43-3.23; P \u3c .001; SAVR OR, 1.89; 95% CI, 1.42-2.53; P ≤ .001) was higher in patients with systolic HF, whereas the risk of permanent pacemaker implantation (TAVR OR, 0.58; 95% CI, 0.45-0.76; P \u3c .001; SAVR OR, 0.58; 95% CI, 0.40-0.84; P = .004) was lower following aortic valve procedures. In TAVR, the risk of acute deep vein thrombosis and kidney injury was higher, although not statistically significant, in patients with systolic HF than in those with diastolic HF. CONCLUSION: These outcomes suggest that chronic HF types do not incur statistically significant hospital mortality risk in patients undergoing TAVR or SAVR

Does the Type of Chronic Heart Failure Impact In-Hospital Outcomes for Aortic Valve Replacement Procedures?

BACKGROUND: This study assessed in-hospital outcomes of patients with chronic systolic, diastolic, or mixed heart failure (HF) undergoing transcatheter aortic valve replacement (TAVR) or surgical aortic valve replacement (SAVR). METHODS: The Nationwide Inpatient Sample database was used to identify patients with aortic stenosis and chronic HF who underwent TAVR or SAVR between 2012 and 2015. Propensity score matching and multivariate logistic regression were used to determine outcome risk. RESULTS: A cohort of 9,879 patients with systolic (27.2%), diastolic (52.2%), and mixed (20.6%) chronic HF were included. No statistically significant differences in hospital mortality were noted. Overall, patients with diastolic HF had the shortest hospital stays and lowest costs. Compared with patients with diastolic HF, the risk of acute myocardial infarction (TAVR odds ratio [OR], 1.95; 95% CI, 1.20-3.19; P = .008; SAVR OR, 1.38; 95% CI, 0.98-1.95; P = .067) and cardiogenic shock (TAVR OR, 2.15; 95% CI, 1.43-3.23; P \u3c .001; SAVR OR, 1.89; 95% CI, 1.42-2.53; P ≤ .001) was higher in patients with systolic HF, whereas the risk of permanent pacemaker implantation (TAVR OR, 0.58; 95% CI, 0.45-0.76; P \u3c .001; SAVR OR, 0.58; 95% CI, 0.40-0.84; P = .004) was lower following aortic valve procedures. In TAVR, the risk of acute deep vein thrombosis and kidney injury was higher, although not statistically significant, in patients with systolic HF than in those with diastolic HF. CONCLUSION: These outcomes suggest that chronic HF types do not incur statistically significant hospital mortality risk in patients undergoing TAVR or SAVR

History, Commemoration, and Belief: Abraham Lincoln in American Memory, 1945-2001

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91765/1/Schuman-History_Commemoration_Belief.pd

Antimicrobial and Efflux Pump Inhibitory Activity of Caffeoylquinic Acids from Artemisia absinthium against Gram-Positive Pathogenic Bacteria

Background: Traditional antibiotics are increasingly suffering from the emergence of multidrug resistance amongst pathogenic bacteria leading to a range of novel approaches to control microbial infections being investigated as potential alternative treatments. One plausible antimicrobial alternative could be the combination of conventional antimicrobial agents/antibiotics with small molecules which block multidrug efflux systems known as efflux pump inhibitors. Bioassay-driven purification and structural determination of compounds from plant sources have yielded a number of pump inhibitors which acted against gram positive bacteria. Methodology/Principal Findings: In this study we report the identification and characterization of 4′,5′-O-dicaffeoylquinic acid (4′,5′-ODCQA) from Artemisia absinthium as a pump inhibitor with a potential of targeting efflux systems in a wide panel of Gram-positive human pathogenic bacteria. Separation and identification of phenolic compounds (chlorogenic acid, 3′,5′-ODCQA, 4′,5′-ODCQA) was based on hyphenated chromatographic techniques such as liquid chromatography with post column solid-phase extraction coupled with nuclear magnetic resonance spectroscopy and mass spectroscopy. Microbial susceptibility testing and potentiation of well know pump substrates revealed at least two active compounds; chlorogenic acid with weak antimicrobial activity and 4′,5′-ODCQA with pump inhibitory activity whereas 3′,5′-ODCQA was ineffective. These intitial findings were further validated with checkerboard, berberine accumulation efflux assays using efflux-related phenotypes and clinical isolates as well as molecular modeling methodology. Conclusions/Significance: These techniques facilitated the direct analysis of the active components from plant extracts, as well as dramatically reduced the time needed to analyze the compounds, without the need for prior isolation. The calculated energetics of the docking poses supported the biological information for the inhibitory capabilities of 4′,5′-ODCQA and furthermore contributed evidence that CQAs show a preferential binding to Major Facilitator Super family efflux systems, a key multidrug resistance determinant in gram-positive bacteria.National Institutes of Health (U.S.) (grant R01GM59903)National Institutes of Health (U.S.) (grant R01AI050875)Netherlands Organization for Scientific Research (VICI grant 700.56.442)Massachusetts Technology Transfer Center (MTTC)National Institutes of Health (U.S.) (grant 5U54MH084690-02

Moving in the anthropocene: global reductions in terrestrial mammalian movements

Animal movement is fundamental for ecosystem functioning and species survival, yet the effects of the anthropogenic footprint on animal movements have not been estimated across species. Using a unique GPS-tracking database of 803 individuals across 57 species, we found that movements of mammals in areas with a comparatively high human footprint were on average one-half to one-third the extent of their movements in areas with a low human footprint. We attribute this reduction to behavioral changes of individual animals and to the exclusion of species with long-range movements from areas with higher human impact. Global loss of vagility alters a key ecological trait of animals that affects not only population persistence but also ecosystem processes such as predator-prey interactions, nutrient cycling, and disease transmission