267 research outputs found
Probing Selectivity and Creating Structural Diversity Through Hybrid Polyketide Synthases
Engineering polyketide synthases (PKS) to produce new metabolites requires an understanding of catalytic points of failure during substrate processing. Growing evidence indicates the thioesterase (TE) domain as a significant bottleneck within engineered PKS systems. We created a series of hybrid PKS modules bearing exchanged TE domains from heterologous pathways and challenged them with both native and nonânative polyketide substrates. Reactions pairing wildtype PKS modules with nonânative substrates primarily resulted in poor conversions to anticipated macrolactones. Likewise, product formation with native substrates and hybrid PKS modules bearing nonâcognate TE domains was severely reduced. In contrast, nonânative substrates were converted by most hybrid modules containing a substrate compatible TE, directly implicating this domain as the major catalytic gatekeeper and highlighting its value as a target for protein engineering to improve analog production in PKS pathways.Improved catalysis with engineered polyketide synthases: Pairing wildâtype polyketide synthases with nonânative substrates largely failed to produce the anticipated products. A series of hybrid modules bearing heterologous thioesterase domains were generated and employed to alleviate the observed catalytic bottleneck, resulting in the efficient processing of nonânative substrates and an unexpected path to product diversity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156208/3/anie202004991-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156208/2/anie202004991_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156208/1/anie202004991.pd
Probing Selectivity and Creating Structural Diversity Through Hybrid Polyketide Synthases
Engineering polyketide synthases (PKS) to produce new metabolites requires an understanding of catalytic points of failure during substrate processing. Growing evidence indicates the thioesterase (TE) domain as a significant bottleneck within engineered PKS systems. We created a series of hybrid PKS modules bearing exchanged TE domains from heterologous pathways and challenged them with both native and nonânative polyketide substrates. Reactions pairing wildtype PKS modules with nonânative substrates primarily resulted in poor conversions to anticipated macrolactones. Likewise, product formation with native substrates and hybrid PKS modules bearing nonâcognate TE domains was severely reduced. In contrast, nonânative substrates were converted by most hybrid modules containing a substrate compatible TE, directly implicating this domain as the major catalytic gatekeeper and highlighting its value as a target for protein engineering to improve analog production in PKS pathways.Improved catalysis with engineered polyketide synthases: Pairing wildâtype polyketide synthases with nonânative substrates largely failed to produce the anticipated products. A series of hybrid modules bearing heterologous thioesterase domains were generated and employed to alleviate the observed catalytic bottleneck, resulting in the efficient processing of nonânative substrates and an unexpected path to product diversity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156161/2/ange202004991-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156161/1/ange202004991.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156161/3/ange202004991_am.pd
Waldo Lake Research in 2004
The Willamette National Forest has worked with Portland State University, Center for Lakes and Reservoirs (PSU) and the University of Oregon (UO) to investigate ecosystem changes, provide guidance on long-term monitoring methods, assess monitoring data, develop predictive water quality models, and conduct research that will lead to better protection and understanding of the Waldo Lake ecosystem. This report summarizes the second year of collaborative PSU-UO research at Waldo Lake. Research has focused on understanding physical, chemical and biological characteristics of Waldo Lake across a range of spatial and temporal scales. Research tasks that continued from 2003 into 2004 included temperature monitoring, hydrodynamic and water quality model development, climate and hydrological forcing scenario investigation, bathymetric map refinement, and analysis of phytoplankton and zooplankton community changes. Research tasks initiated in 2004 included evaluation of wavelength-specific light attenuation, diel phytoplankton and zooplankton vertical distribution patterns, phytoplankton photoinhibition and photoprotection, and the role of mixotrophy in the pelagic microbial food web.
Preliminary efforts were made to characterize Waldo Lake benthos through assessment of algal species diversity and chemical composition of the benthic community, as very little is currently known about the Waldo Lake benthic ecosystem. In addition, an attempt was made to map benthic substrate types through reinterpretation of data collected during the 2003 bathymetric survey
What is the structure of the Roper resonance?
We investigate the structure of the nucleon resonance N^*(1440) (Roper)
within a coupled-channel meson exchange model for pion-nucleon scattering. The
coupling to pipiN states is realized effectively by the coupling to the sigmaN,
piDelta and rhoN channels. The interaction within and between these channels is
derived from an effective Lagrangian based on a chirally symmetric Lagrangian,
which is supplemented by well known terms for the coupling of the Delta isobar,
the omega meson and the 'sigma', which is the name given here to the strong
correlation of two pions in the scalar-isoscalar channel. In this model the
Roper resonance can be described by meson-baryon dynamics alone; no genuine
N^*(1440) (3 quark) resonance is needed in order to fit piN phase shifts and
inelasticities.Comment: 55 pages, 14 figure
Discovery of interlayer plasmon polaron in graphene/WS heterostructures
Harnessing electronic excitations involving coherent coupling to bosonic
modes is essential for the design and control of emergent phenomena in quantum
materials [1]. In situations where charge carriers induce a lattice distortion
due to the electron-phonon interaction, the conducting states get "dressed".
This leads to the formation of polaronic quasiparticles that dramatically
impact charge transport, surface reactivity, thermoelectric and optical
properties, as observed in a variety of crystals and interfaces composed of
polar materials [2-6]. Similarly, when oscillations of the charge density
couple to conduction electrons the more elusive plasmon polaron emerges [7],
which has been detected in electron-doped semiconductors [8-10]. However, the
exploration of polaronic effects on low energy excitations is still in its
infancy in two-dimensional (2D) materials. Here, we present the discovery of an
interlayer plasmon polaron in heterostructures composed of graphene on top of
SL WS. By using micro-focused angle-resolved photoemission spectroscopy
(microARPES) during in situ doping of the top graphene layer, we observe a
strong quasiparticle peak accompanied by several carrier density-dependent
shake-off replicas around the SL WS conduction band minimum (CBM). Our
results are explained by an effective many-body model in terms of a coupling
between SL WS conduction electrons and graphene plasmon modes. It is
important to take into account the presence of such interlayer collective
modes, as they have profound consequences for the electronic and optical
properties of heterostructures that are routinely explored in many device
architectures involving 2D transition metal dichalcogenides (TMDs) [11-15].Comment: 25 pages, 9 figures including Supporting Informatio
Photo-physics and electronic structure of lateral graphene/MoS2 and metal/MoS2 junctions
Integration of semiconducting transition metal dichalcogenides (TMDs) into
functional optoelectronic circuitries requires an understanding of the charge
transfer across the interface between the TMD and the contacting material.
Here, we use spatially resolved photocurrent microscopy to demonstrate
electronic uniformity at the epitaxial graphene/molybdenum disulfide (EG/MoS2)
interface. A 10x larger photocurrent is extracted at the EG/MoS2 interface when
compared to metal (Ti/Au) /MoS2 interface. This is supported by semi-local
density-functional theory (DFT), which predicts the Schottky barrier at the
EG/MoS2 interface to be ~2x lower than Ti/MoS2. We provide a direct
visualization of a 2D material Schottky barrier through combination of angle
resolved photoemission spectroscopy with spatial resolution selected to be ~300
nm (nano-ARPES) and DFT calculations. A bending of ~500 meV over a length scale
of ~2-3 micrometer in the valence band maximum of MoS2 is observed via
nano-ARPES. We explicate a correlation between experimental demonstration and
theoretical predictions of barriers at graphene/TMD interfaces. Spatially
resolved photocurrent mapping allows for directly visualizing the uniformity of
built-in electric fields at heterostructure interfaces, providing a guide for
microscopic engineering of charge transport across heterointerfaces. This
simple probe-based technique also speaks directly to the 2D synthesis community
to elucidate electronic uniformity at domain boundaries alongside morphological
uniformity over large areas
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