593 research outputs found
Bacterial Hsp70 resolves misfolded states and accelerates productive folding of a multi-domain protein
The ATP-dependent Hsp70 chaperones (DnaK in E. coli) mediate protein folding in cooperation with J proteins and nucleotide exchange factors (E. coli DnaJ and GrpE, respectively). The Hsp70 system prevents protein aggregation and increases folding yields. Whether it also enhances the rate of folding remains unclear. Here we show that DnaK/DnaJ/GrpE accelerate the folding of the multi-domain protein firefly luciferase (FLuc) 20-fold over the rate of spontaneous folding measured in the absence of aggregation. Analysis by single-pair FRET and hydrogen/deuterium exchange identified inter-domain misfolding as the cause of slow folding. DnaK binding expands the misfolded region and thereby resolves the kinetically-trapped intermediates, with folding occurring upon GrpE-mediated release. In each round of release DnaK commits a fraction of FLuc to fast folding, circumventing misfolding. We suggest that by resolving misfolding and accelerating productive folding, the bacterial Hsp70 system can maintain proteins in their native states under otherwise denaturing stress conditions. The Hsp70 system prevents protein aggregation and increases folding yields, but it is unknown whether it also enhances the rate of folding. Here the authors combine refolding assays, FRET and hydrogen/deuterium exchange-mass spectrometry measurements to study the folding of firefly luciferase and find that the bacterial Hsp70 actively promotes the folding of this multi-domain protein
High-Order Multipole Radiation from Quantum Hall States in Dirac Materials
We investigate the optical response of strongly disordered quantum Hall
states in two-dimensional Dirac materials and find qualitatively different
effects in the radiation properties of the bulk versus the edge. We show that
the far-field radiation from the edge is characterized by large multipole
moments (> 50) due to the efficient transfer of angular momentum from the
electrons into the scattered light. The maximum multipole transition moment is
a direct measure of the coherence length of the edge states. Accessing these
multipole transitions would provide new tools for optical spectroscopy and
control of quantum Hall edge states. On the other hand, the far-field radiation
from the bulk appears as random dipole emission with spectral properties that
vary with the local disorder potential. We determine the conditions under which
this bulk radiation can be used to image the disorder landscape. Such optical
measurements can probe sub-micron length scales over large areas and provide
complementary information to scanning probe techniques. Spatially resolving
this bulk radiation would serve as a novel probe of the percolation transition
near half-filling.Comment: v2: 8 pages, 4 figure
Controlling a mesoscopic spin environment by quantum bit manipulation
We present a unified description of cooling and manipulation of a mesoscopic
bath of nuclear spins via coupling to a single quantum system of electronic
spin (quantum bit). We show that a bath cooled by the quantum bit rapidly
saturates. Although the resulting saturated states of the spin bath (``dark
states'') generally have low degrees of polarization and purity, their symmetry
properties make them a valuable resource for the coherent manipulation of
quantum bits. Specifically, we demonstrate that the dark states of nuclear
ensembles can be used to coherently control the system-bath interaction and to
provide a robust, long-lived quantum memory for qubit states.Comment: 4 pages, 3 figure
The parameter at three loops and elliptic integrals
We describe the analytic calculation of the master integrals required to
compute the two-mass three-loop corrections to the parameter. In
particular, we present the calculation of the master integrals for which the
corresponding differential equations do not factorize to first order. The
homogeneous solutions to these differential equations are obtained in terms of
hypergeometric functions at rational argument. These hypergeometric functions
can further be mapped to complete elliptic integrals, and the inhomogeneous
solutions are expressed in terms of a new class of integrals of combined
iterative non-iterative nature.Comment: 14 pages Latex, 7 figures, to appear in the Proceedings of "Loops and
Legs in Quantum Field Theory - LL 2018", 29 April - 4 May 2018, Po
Proposed Rabi-Kondo Correlated State in a Laser-Driven Semiconductor Quantum Dot
Spin exchange between a single-electron charged quantum dot and itinerant
electrons leads to an emergence of Kondo correlations. When the quantum dot is
driven resonantly by weak laser light, the resulting emission spectrum allows
for a direct probe of these correlations. In the opposite limit of vanishing
exchange interaction and strong laser drive, the quantum dot exhibits coherent
oscillations between the single-spin and optically excited states. Here, we
show that the interplay between strong exchange and non-perturbative laser
coupling leads to the formation of a new nonequilibrium quantum-correlated
state, characterized by the emergence of a laser-induced secondary spin
screening cloud, and examine the implications for the emission spectrum
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