503 research outputs found
Interactions between Small Heat Shock Protein Subunits and Substrate in Small Heat Shock Protein-Substrate Complexes
Small heat shock proteins (sHSPs) are dynamic oligomeric
proteins that bind unfolding proteins and protect
them from irreversible aggregation. This binding results
in the formation of sHSP-substrate complexes from
which substrate can later be refolded. Interactions between
sHSP and substrate in sHSP-substrate complexes
and the mechanism by which substrate is transferred to
ATP-dependent chaperones for refolding are poorly defined.
We have established C-terminal affinity-tagged
sHSPs from a eukaryote (pea HSP18.1) and a prokaryote
(Synechocystis HSP16.6) as tools to investigate these issues.
We demonstrate that sHSP subunit exchange for
HSP18.1 and HSP16.6 is temperature-dependent and
rapid at the optimal growth temperature for the organism
of origin. Increasing the ratio of sHSP to substrate
during substrate denaturation decreased sHSP-substrate
complex size, and accordingly, addition of substrate
to pre-formed sHSP-substrate complexes increased
complex size. However, the size of pre-formed
sHSP-substrate complexes could not be reduced by addition
of more sHSP, and substrate could not be observed
to transfer to added sHSP, although added sHSP
subunits continued to exchange with subunits in sHSPsubstrate
complexes. Thus, although some number of
sHSP subunits within complexes remain dynamic and
may be important for complex structure/solubility, association
of substrate with the sHSP does not appear to be
similarly dynamic. These observations are consistent
with a model in which ATP-dependent chaperones associate
directly with sHSP-bound substrate to initiate
refolding
Quantum Oscillations of Photocurrents in HgTe Quantum Wells with Dirac and Parabolic Dispersions
We report on the observation of magneto-oscillations of terahertz radiation
induced photocurrent in HgTe/HgCdTe quantum wells (QWs) of different widths,
which are characterized by a Dirac-like, inverted and normal parabolic band
structure. The photocurrent data are accompanied by measurements of
photoresistance (photoconductivity), radiation transmission, as well as
magneto-transport. We develop a microscopic model of a cyclotron-resonance
assisted photogalvanic effect, which describes main experimental findings. We
demonstrate that the quantum oscillations of the photocurrent are caused by the
crossing of Fermi level by Landau levels resulting in the oscillations of spin
polarization and electron mobilities in spin subbands. Theory explains a
photocurrent direction reversal with the variation of magnetic field observed
in experiment. We describe the photoconductivity oscillations related with the
thermal suppression of the Shubnikov-de Haas effect.Comment: 16 pages, 13 figure
A gradient of nutrient enrichment reveals nonlinear impacts of fertilization on Arctic plant diversity and ecosystem function
© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ecology and Evolution 7 (2017): 2449–2460, doi:10.1002/ece3.2863.Rapid environmental change at high latitudes is predicted to greatly alter the diversity, structure, and function of plant communities, resulting in changes in the pools and fluxes of nutrients. In Arctic tundra, increased nitrogen (N) and phosphorus (P) availability accompanying warming is known to impact plant diversity and ecosystem function; however, to date, most studies examining Arctic nutrient enrichment focus on the impact of relatively large (>25x estimated naturally occurring N enrichment) doses of nutrients on plant community composition and net primary productivity. To understand the impacts of Arctic nutrient enrichment, we examined plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming-induced fertilization. In addition, we compared our measured ecosystem CO2 flux data to a widely used Arctic ecosystem exchange model to investigate the ability to predict the capacity for CO2 exchange with nutrient addition. We observed declines in abundance-weighted plant diversity at low levels of nutrient enrichment, but species richness and the capacity for ecosystem carbon uptake did not change until the highest level of fertilization. When we compared our measured data to the model, we found that the model explained roughly 30%–50% of the variance in the observed data, depending on the flux variable, and the relationship weakened at high levels of enrichment. Our results suggest that while a relatively small amount of nutrient enrichment impacts plant diversity, only relatively large levels of fertilization—over an order of magnitude or more than warming-induced rates—significantly alter the capacity for tundra CO2 exchange. Overall, our findings highlight the value of measuring and modeling the impacts of a nutrient enrichment gradient, as warming-related nutrient availability may impact ecosystems differently than single-level fertilization experiments.NASA Terrestrial Ecology Grant Number: NNX12AK83G;
National Science Foundation Division of Graduate Education Grant Number: DGE-11-4415
The Role of Parvalbumin-positive Interneurons in Auditory Steady-State Response Deficits in Schizophrenia
© The Author(s) 2019. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.Despite an increasing body of evidence demonstrating subcellular alterations in parvalbumin-positive (PV+) interneurons in schizophrenia, their functional consequences remain elusive. Since PV+ interneurons are involved in the generation of fast cortical rhythms, these changes have been hypothesized to contribute to well-established alterations of beta and gamma range oscillations in patients suffering from schizophrenia. However, the precise role of these alterations and the role of different subtypes of PV+ interneurons is still unclear. Here we used a computational model of auditory steady-state response (ASSR) deficits in schizophrenia. We investigated the differential effects of decelerated synaptic dynamics, caused by subcellular alterations at two subtypes of PV+ interneurons: basket cells and chandelier cells. Our simulations suggest that subcellular alterations at basket cell synapses rather than chandelier cell synapses are the main contributor to these deficits. Particularly, basket cells might serve as target for innovative therapeutic interventions aiming at reversing the oscillatory deficits.Peer reviewe
Model for end-stage liver disease (MELD) exception guidelines: Results and recommendations from the MELD exception study group and conference (MESSAGE) for the approval of patients who need liver transplantation with diseases not considered by the standard MELD formula
No abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55914/1/20979_ftp.pd
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