146,395 research outputs found
Enhanced Diffusion of Enzymes that Catalyze Exothermic Reactions
Enzymes have been recently found to exhibit enhanced diffusion due to their
catalytic activities. A recent experiment [C. Riedel et al., Nature 517, 227
(2015)] has found evidence that suggests this phenomenon might be controlled by
the degree of exothermicity of the catalytic reaction involved. Four mechanisms
that can lead to this effect, namely, self-thermophoresis, boost in kinetic
energy, stochastic swimming, and collective heating, are critically discussed,
and it is shown that only the last two could be strong enough to account for
the observations. The resulting quantitative description is used to examine the
biological significance of the effect.Comment: To appear in PR
Extended surfaces modulate and can catalyze hydrophobic effects
Interfaces are a most common motif in complex systems. To understand how the
presence of interfaces affect hydrophobic phenomena, we use molecular
simulations and theory to study hydration of solutes at interfaces. The solutes
range in size from sub-nanometer to a few nanometers. The interfaces are
self-assembled monolayers with a range of chemistries, from hydrophilic to
hydrophobic. We show that the driving force for assembly in the vicinity of a
hydrophobic surface is weaker than that in bulk water, and decreases with
increasing temperature, in contrast to that in the bulk. We explain these
distinct features in terms of an interplay between interfacial fluctuations and
excluded volume effects---the physics encoded in Lum-Chandler-Weeks theory [J.
Phys. Chem. B 103, 4570--4577 (1999)]. Our results suggest a catalytic role for
hydrophobic interfaces in the unfolding of proteins, for example, in the
interior of chaperonins and in amyloid formation.Comment: 22 pages, 5 figure
Degree Variance and Emotional Strategies Catalyze Cooperation in Dynamic Signed Networks
We study the problem of the emergence of cooperation in dynamic signed
networks where agent strategies coevolve with relational signs and network
topology. Running simulations based on an agent-based model, we compare results
obtained in a regular lattice initialization with those obtained on a
comparable random network initialization. We show that the increased degree
heterogeneity at the outset enlarges the parametric conditions in which
cooperation survives in the long run. Furthermore, we show how the presence of
sign-dependent emotional strategies catalyze the evolution of cooperation with
both network topology initializations.Comment: 16 Pages, Proceeding of the European Conference on Modelling and
Simumatio
Driving Value in Medicaid Primary Care: The Role of Shared Support Networks for Physician Practices
Examines the challenges of transforming small primary care practices under healthcare reform and options for Medicaid to drive changes through practice supports to help implement and sustain new models of care or catalyze investments in new systems
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Enzyme-catalyzed cationic epoxide rearrangements in quinolone alkaloid biosynthesis.
Epoxides are highly useful synthons and biosynthons for the construction of complex natural products during total synthesis and biosynthesis, respectively. Among enzyme-catalyzed epoxide transformations, a reaction that is notably missing, in regard to the synthetic toolbox, is cationic rearrangement that takes place under strong acid. This is a challenging transformation for enzyme catalysis, as stabilization of the carbocation intermediate upon epoxide cleavage is required. Here, we discovered two Brønsted acid enzymes that can catalyze two unprecedented epoxide transformations in biology. PenF from the penigequinolone pathway catalyzes a cationic epoxide rearrangement under physiological conditions to generate a quaternary carbon center, while AsqO from the aspoquinolone pathway catalyzes a 3-exo-tet cyclization to forge a cyclopropane-tetrahydrofuran ring system. The discovery of these new epoxide-modifying enzymes further highlights the versatility of epoxides in complexity generation during natural product biosynthesis
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Draft Genome Sequences of Salmonella enterica Serovar Typhimurium LT2 with Deleted Chitinases That Are Emerging Virulence Factors.
Chitinases are glycosyl hydrolases that catalyze the hydrolysis of the β-1,4 linkages in complex carbohydrates and those that contain GlcNAc. These enzymes are considered emerging virulence factors during infection because the host glycan changes. This is the release of four single chitinase deletion mutants in Salmonella enterica serovar Typhimurium LT2
ruvA Mutants that resolve Holliday junctions but do not reverse replication forks
RuvAB and RuvABC complexes catalyze branch migration and resolution of Holliday junctions (HJs) respectively. In addition to their action in the last steps of homologous recombination, they process HJs made by replication fork reversal, a reaction which occurs at inactivated replication forks by the annealing of blocked leading and lagging strand ends. RuvAB was recently proposed to bind replication forks and directly catalyze their conversion into HJs. We report here the isolation and characterization of two separation-of-function ruvA mutants that resolve HJs, based on their capacity to promote conjugational recombination and recombinational repair of UV and mitomycin C lesions, but have lost the capacity to reverse forks. In vivo and in vitro evidence indicate that the ruvA mutations affect DNA binding and the stimulation of RuvB helicase activity. This work shows that RuvA's actions at forks and at HJs can be genetically separated, and that RuvA mutants compromised for fork reversal remain fully capable of homologous recombination
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