1,405 research outputs found
Structural basis of the allosteric trigger of the Hsp70 chaperone proteins.
This work solves a decades-old dilemma that stood in the way of understanding the allosteric mechanism of Hsp70 (heat shock 70 kDa) chaperone proteins. Hsp70s are central to protein folding, refolding, and trafficking in organisms ranging from Archae to Homo Sapiens, both at normal and at stressed cellular conditions. Hsp70s are comprised of two main domains: a 44 kDa N-terminal nucleotide-binding domain (NBD), and a 25 kDa substrate-binding domain (SBD) that harbors the substrate binding site. The nucleotide binding site in the NBD and the substrate binding site in the SBD are allosterically linked: ADP binding promotes substrate binding, while ATP binding promotes substrate release. It has long been a goal of structural biology to characterize the nature of the allosteric coupling in these proteins. However, even the most sophisticated X-ray crystallography studies of the isolated NBD could show no difference in overall conformation between the ATP and ADP state. Hence the dilemma: how is the state of the nucleotide communicated between NBD and SBD? The solution of the dilemma is especially interesting in light of the fact that Hsp70s are ancient proteins, and amongst the first allosteric proteins in nature.Here we report a solution NMR study of the NBD of the Hsp70 from Thermus thermophilus, in the APO, ADP and AMP-PNP states, where the latter is a non-hydrolysable ATP analogue. Using the modern NMR methods of residual dipolar coupling analysis, we discovered that the nucleotide binding cleft opens up by as much as 20 degrees between the AMP-PNP (closed) and ADP (open) state. We also discover that a surface cleft, hypothesized to be essential for the allosteric coupling between NBD and SBD, echoes these changes. Hence, the nature of the allosteric trigger and coupling for Hsp70 chaperones is revealed here for the first time, solving the dilemma
Synthesis of the Einstein-Podolsky-Rosen entanglement in a sequence of two single-mode squeezers
Synthesis of the Einstein-Podolsky-Rosen entangled state --- the primary
entangled resource in continuous-variable quantum-optical information
processing --- is a technological challenge of great importance. Here we
propose and implement a new scheme of generating this state. Two nonlinear
optical crystals, positioned back-to-back in the waist of a pump beam, function
as single-pass degenerate optical parametric amplifiers and produce single-mode
squeezed vacuum states in orthogonal polarization modes, but in the same
spatiotemporal mode. A subsequent pair of waveplates acts as a beam splitter,
entangling the two polarization modes to generate the Einstein-Podolsky-Rosen
state. This technique takes advantage of the strong nonlinearity associated
with type-I phase-matching configuration while at the same time eliminating the
need for actively stabilizing the optical phase between the two squeezers,
which typically arises if these squeezers are spatially separated. We
demonstrate our method in an experiment, preparing a 1.4 dB two-mode squeezed
state and characterizing it via two-mode homodyne tomography.Comment: 4 pages, 3 figure
Information and Information Technologies in Conflict Management
This paper analyzes information and modern information technologies as applied in different organizational environment and considers the content and peculiarities of conflict management process based on implementation of communicative scenarios. Currently, the need for escalated organizational transformations has become imminent, taking into account the intensifying development of the differentiated information society, which requires properly interactive and transparent policy-making. Correct understanding of information and effective implementation of information technologies is a rational attempt to harmonize the modern organizational environment reducing the level of conflict and improving efficiency indexes
Undoing the effect of loss on quantum entanglement
Entanglement distillation is a process via which the strength and purity of
quantum entanglement can be increased probabilistically. It is a key step in
many quantum communication and computation protocols. In particular,
entanglement distillation is a necessary component of the quantum repeater, a
device which counters the degradation of entanglement that inevitably occurs
due to losses in a communication line. Here we report an experiment on
distilling the Einstein-Podolsky-Rosen (EPR) state of light, the workhorse of
continuous-variable entanglement, using the technique of noiseless
amplification. In contrast to previous implementations, the entanglement
enhancement factor achievable by our technique is not fundamentally limited and
permits recovering an EPR state with a macroscopic level of entanglement no
matter how low the initial entanglement or how high the loss may be. In
particular, we recover the original level of entanglement after one of the EPR
modes has passed through a channel with a loss factor of 20. The level of
entanglement in our distilled state is higher than that achievable by direct
transmission of any state through a similar loss channel. This is a key
bench-marking step towards the realization of a practical continuous-variable
quantum repeater and other CV quantum protocols.Comment: 8 pages, 5 figure
Phase Randomness in a Semiconductor Laser: the Issue of Quantum Random Number Generation
Gain-switched lasers are in demand in numerous quantum applications,
particularly, in systems of quantum key distribution and in various optical
quantum random number generators. The reason for this popularity is natural
phase randomization between gain-switched laser pulses. The idea of such
randomization has become so familiar that most authors use it without regard to
the features of the laser operation mode they use. However, at high repetition
rates of laser pulses or when pulses are generated at a bias current close to
the threshold, the phase randomization condition may be violated. This paper
describes theoretical and experimental methods for estimating the degree of
phase randomization in a gain-switched laser. We consider in detail different
situations of laser pulse interference and show that the interference signal
remains quantum in nature even in the presence of classical phase drift in the
interferometer provided that the phase diffusion in a laser is efficient
enough. Moreover, we formulate the relationship between the previously
introduced quantum reduction factor and the leftover hash lemma. Using this
relationship, we develop a method to estimate the quantum noise contribution to
the interference signal in the presence of phase correlations. Finally, we
introduce a simple experimental method based on the analysis of statistical
interference fringes, providing more detailed information about the
probabilistic properties of laser pulse interference
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