Evidence for a model of agonist-induced activation of 5-hydroxytryptamine 2A serotonin receptors that involves the disruption of a strong ionic interaction between helices 3 and 6

5-Hydroxytryptamine 2A (5-HT2A) receptors are essential for the actions of serotonin (5-hydroxytryptamine (5-HT)) on physiological processes as diverse as vascular smooth muscle contraction, platelet aggregation, perception, and emotion. In this study, we investigated the molecular mechanism(s) by which 5-HT activates 5-HT2A receptors using a combination of approaches including site-directed mutagenesis, molecular modeling, and pharmacological analysis using the sensitive, cell-based functional assay R-SAT. Alanine-scanning mutagenesis of residues close to the intracellular end of H6 of the 5-HT2A receptor implicated glutamate Glu-318(6.30) in receptor activation, as also predicted by a newly constructed molecular model of the 5-HT2A receptor, which was based on the x-ray structure of bovine rhodopsin. Close examination of the molecular model suggested that Glu-318(6.30) could form a strong ionic interaction with Arg-173(3.50) of the highly conserved "(D/E)RY motif" located at the interface between the third transmembrane segment and the second intracellular loop (i2). A direct prediction of this hypothesis, that disrupting this ionic interaction by an E318(6.30)R mutation would lead to a highly constitutively active receptor with enhanced affinity for agonist, was confirmed using R-SAT. Taken together, these results predict that the disruption of a strong ionic interaction between transmembrane helices 3 and 6 of 5-HT2A receptors is essential for agonist-induced receptor activation and, as recently predicted by ourselves (B. L. Roth and D. A. Shapiro (2001) Expert Opin. Ther. Targets 5, 685-695) and others, that this may represent a general mechanism of activation for many, but not all, G-protein-coupled receptors

Erratum: Evidence for a model of agonist-induced activation of 5-hydroxytryptamine 2A serotonin receptors that involves the disruption of a strong ionic interaction between helices 3 and 6 (Journal of Biological Chemistry (2002) 277 (11441-11449))

[No abstract available

Dark soliton states of Bose-Einstein condensates in anisotropic traps

Dark soliton states of Bose-Einstein condensates in harmonic traps are studied both analytically and computationally by the direct solution of the Gross-Pitaevskii equation in three dimensions. The ground and self-consistent excited states are found numerically by relaxation in imaginary time. The energy of a stationary soliton in a harmonic trap is shown to be independent of density and geometry for large numbers of atoms. Large amplitude field modulation at a frequency resonant with the energy of a dark soliton is found to give rise to a state with multiple vortices. The Bogoliubov excitation spectrum of the soliton state contains complex frequencies, which disappear for sufficiently small numbers of atoms or large transverse confinement. The relationship between these complex modes and the snake instability is investigated numerically by propagation in real time.Comment: 11 pages, 8 embedded figures (two in color

Spin-based all-optical quantum computation with quantum dots: understanding and suppressing decoherence

We present an all-optical implementation of quantum computation using semiconductor quantum dots. Quantum memory is represented by the spin of an excess electron stored in each dot. Two-qubit gates are realized by switching on trion-trion interactions between different dots. State selectivity is achieved via conditional laser excitation exploiting Pauli exclusion principle. Read-out is performed via a quantum-jump technique. We analyze the effect on our scheme's performance of the main imperfections present in real quantum dots: exciton decay, hole mixing and phonon decoherence. We introduce an adiabatic gate procedure that allows one to circumvent these effects, and evaluate quantitatively its fidelity

Practice level factors associated with enhanced engagement with practice facilitators; findings from the heart health now study

Background: Practice facilitation is a promising strategy to enhance care processes and outcomes in primary care settings. It requires that practices and their facilitators engage as teams to drive improvement. In this analysis, we explored the practice and facilitator factors associated with greater team engagement at the mid-point of a 12-month practice facilitation intervention focused on implementing cardiovascular prevention activities in practice. Understanding factors associated with greater engagement with facilitators in practice-based quality improvement can assist practice facilitation programs with planning and resource allocation. Methods: One hundred thirty-six ambulatory care small to medium sized primary care practices that participated in the EvidenceNow initiative's NC Cooperative, named Heart Health Now (HHN), fit the eligibility criteria for this analysis. We explored the practice and facilitator factors associated with greater team engagement at the mid-point of a 12-month intervention using a retrospective cohort design that included baseline survey data, monthly practice activity implementation data and information about facilitator's experience. Generalized linear mixed-effects models (GLMMs) identified variables associated with greater odds of team engagement using an ordinal scale for level of team engagement. Results: Among our practice cohort, over half were clinician-owned and 27% were Federally Qualified Health Centers. The mean number of clinicians was 4.9 (SD 4.2) and approximately 40% of practices were in Medically Underserved Areas (MUA). GLMMs identified a best fit model. The Model presented as odd ratios and 95% confidence intervals suggests greater odds ratios of higher team engagement with greater practice QI leadership 17.31 (5.24-57.19), [0.00], and practice location in a MUA 7.25 (1.8-29.20), [0.005]. No facilitator characteristics were independently associated with greater engagement. Conclusions: Our analysis provides information for practice facilitation stakeholders to consider when considering which practices may be more amendable to embracing facilitation services

Modernization and Its Discontents

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67022/2/10.1177_000276427702100208.pd

Conformational Determinants of Phosphotyrosine Peptides Complexed with the Src SH2 Domain

The inhibition of specific SH2 domain mediated protein-protein interactions as an effective chemotherapeutic approach in the treatment of diseases remains a challenge. That different conformations of peptide-ligands are preferred by different SH2 domains is an underappreciated observation from the structural analysis of phosphotyrosine peptide binding to SH2 domains that may aid in future drug design. To explore the nature of ligand binding, we use simulated annealing (SA) to sample the conformational space of phosphotyrosine-containing peptides complexed with the Src SH2 domain. While in good agreement with the crystallographic and NMR studies of high-affinity phosphopeptide-SH2 domain complexes, the results suggest that the structural basis for phopsphopeptide- Src SH2 interactions is more complex than the “two-pronged plug two-hole socket” model. A systematic study of peptides of type pYEEX, where pY is phosphotyrosine and X is a hydrophobic residue, indicates that these peptides can assume two conformations, one extended and one helical, representing the balance between the interaction of residue X with the hydrophobic hole on the surface of the Src SH2 domain, and its contribution to the inherent tendency of the two glutamic acids to form an α-helix. In contrast, a β-turn conformation, almost identical to that observed in the crystal structure of pYVNV bound to the Grb2 SH2 domain, predominates for pYXNX peptides, even in the presence of isoleucine at the third position. While peptide binding affinities, as measured by fluorescence polarization, correlate with the relative proportion of extended peptide conformation, these results suggest a model where all three residues C-terminal to the phosphotyrosine determine the conformation of the bound phosphopeptide. The information obtained in this work can be used in the design of specific SH2 domain inhibitors

Extreme magnification of an individual star at redshift 1.5 by a galaxy-cluster lens

Galaxy-cluster gravitational lenses can magnify background galaxies by a total factor of up to ~50. Here we report an image of an individual star at redshift z = 1.49 (dubbed MACS J1149 Lensed Star 1) magnified by more than ×2,000. A separate image, detected briefly 0.26″ from Lensed Star 1, is probably a counterimage of the first star demagnified for multiple years by an object of ≳3 solar masses in the cluster. For reasonable assumptions about the lensing system, microlensing fluctuations in the stars’ light curves can yield evidence about the mass function of intracluster stars and compact objects, including binary fractions and specific stellar evolution and supernova models. Dark-matter subhaloes or massive compact objects may help to account for the two images’ long-term brightness ratio