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Journal of Chemical Theory and... Oct 2023Aromatic side chains (phenylalanine and tyrosine) of a protein flip by 180° around the - axis (χ dihedral of the side chain), producing two symmetry-equivalent states....
Aromatic side chains (phenylalanine and tyrosine) of a protein flip by 180° around the - axis (χ dihedral of the side chain), producing two symmetry-equivalent states. The study of ring flip dynamics with nuclear magnetic resonance (NMR) experiments helps to understand local conformational fluctuations. Ring flips are categorized as slow (milliseconds and onward) or fast (nanoseconds to near milliseconds) based on timescales accessible to NMR experiments. In this study, we investigated the ability of the infrequent metadynamics approach to estimate the flip rate and discriminate between slow and fast ring flips for eight individual aromatic side chains (F4, Y10, Y21, F22, Y23, F33, Y35, and F45) of the basic pancreatic trypsin inhibitor. Well-tempered metadynamics simulations were performed to estimate the ring-flipping free-energy surfaces for all eight aromatic residues. The results indicate that χ as a standalone collective variable (CV) is not sufficient to obtain computationally consistent results. Inclusion of a complementary CV, such as χ(C-C), solved the problem for most residues and enabled us to classify fast and slow ring flips. This indicates the importance of librational motions in ring flips. Multiple pathways and mechanisms were observed for residues F4, Y10, and F22. Recrossing events were observed for residues F22 and F33, indicating a possible role of friction effects in ring flipping. The results demonstrate the successful application of infrequent metadynamics to estimate ring flip rates and identify certain limitations of the approach.
Topics: Aprotinin; Trypsin Inhibitors; Tyrosine; Phenylalanine; Magnetic Resonance Spectroscopy; Protein Conformation
PubMed: 37698852
DOI: 10.1021/acs.jctc.3c00460 -
Journal of the American Heart... Jan 2022Background The rate of sudden cardiac death (SCD) in Brugada syndrome (BrS) is ≈1%/y. Noninvasive electrocardiographic imaging is a noninvasive mapping system that has...
Background The rate of sudden cardiac death (SCD) in Brugada syndrome (BrS) is ≈1%/y. Noninvasive electrocardiographic imaging is a noninvasive mapping system that has a role in assessing BrS depolarization and repolarization abnormalities. This study aimed to analyze electrocardiographic imaging parameters during ajmaline test (AJT). Methods and Results All consecutive epicardial maps of the right ventricle outflow tract (RVOT-EPI) in BrS with CardioInsight were retrospectively analyzed. (1) RVOT-EPI activation time (RVOT-AT); (2) RVOT-EPI recovery time, and (3) RVOT-EPI activation-recovery interval (RVOT-ARI) were calculated. ∆RVOT-AT, ∆RVOT-EPI recovery time, and ∆RVOT-ARI were defined as the difference in parameters before and after AJT. SCD-BrS patients were defined as individuals presenting a history of aborted SCD. Thirty-nine patients with BrS were retrospectively analyzed and 12 patients (30.8%) were SCD-BrS. After AJT, an increase in both RVOT-AT [105.9 milliseconds versus 65.8 milliseconds, <0.001] and RVOT-EPI recovery time [403.4 milliseconds versus 365.7 milliseconds, <0.001] was observed. No changes occurred in RVOT-ARI [297.5 milliseconds versus 299.9 milliseconds, =0.7]. Before AJT no differences were observed between SCD-BrS and non SCD-BrS in RVOT-AT, RVOT-EPI recovery time, and RVOT-ARI (=0.9, =0.91, =0.86, respectively). Following AJT, SCD-BrS patients showed higher RVOT-AT, higher ∆RVOT-AT, lower RVOT-ARI, and lower ∆RVOT-ARI (<0.001, <0.001, =0.007, =0.002, respectively). At the univariate logistic regression, predictors of SCD-BrS were the following: RVOT-AT after AJT (specificity: 0.74, sensitivity 1.00, area under the curve 0.92); ∆RVOT-AT (specificity: 0.74, sensitivity 0.92, area under the curve 0.86); RVOT-ARI after AJT (specificity 0.96, sensitivity 0.58, area under the curve 0.79), and ∆RVOT-ARI (specificity 0.85, sensitivity 0.67, area under the curve 0.76). Conclusions Noninvasive electrocardiographic imaging can be useful in evaluating the results of AJT in BrS.
Topics: Ajmaline; Brugada Syndrome; Death, Sudden, Cardiac; Electrocardiography; Heart Rate; Humans; Retrospective Studies
PubMed: 35023354
DOI: 10.1161/JAHA.121.024001 -
Proceedings of the National Academy of... Apr 2017Imidazole glycerol phosphate synthase (IGPS) is a V-type allosteric enzyme, meaning that its catalytic rate is critically dependent on activation by its allosteric...
Imidazole glycerol phosphate synthase (IGPS) is a V-type allosteric enzyme, meaning that its catalytic rate is critically dependent on activation by its allosteric ligand, -[(5'-phosphoribulosyl)formimino]-5-aminoimidazole-4-carboxamide ribonucleotide (PRFAR). The allosteric mechanism of IGPS is reliant on millisecond conformational motions for efficient catalysis. We engineered four mutants of IGPS designed to disrupt millisecond motions and allosteric coupling to identify regions that are critical to IGPS function. Multiple-quantum Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiments and NMR chemical shift titrations reveal diminished enzyme flexibility and a reshaping of the allosteric connectivity in each mutant construct, respectively. The functional relevance of the observed motional quenching is confirmed by significant reductions in glutaminase kinetic activity and allosteric ligand binding affinity. This work presents relevant conclusions toward the control of protein allostery and design of unique allosteric sites for potential enzyme inhibitors with regulatory or therapeutic benefit.
Topics: Allosteric Regulation; Aminohydrolases; Bacterial Proteins; Catalysis; Gene Knockdown Techniques; Saccharomyces cerevisiae; Structural Homology, Protein; Thermotoga maritima; beta-Lactam Resistance
PubMed: 28396388
DOI: 10.1073/pnas.1700448114 -
Clinical Pharmacology in Drug... Sep 2022Abrocitinib is a selective Janus kinase 1 inhibitor for the treatment of moderate to severe atopic dermatitis (AD). To assess the relationship between abrocitinib plasma...
Abrocitinib is a selective Janus kinase 1 inhibitor for the treatment of moderate to severe atopic dermatitis (AD). To assess the relationship between abrocitinib plasma concentrations and heart rate (HR)-corrected QT (QTc) and HR and calculate the effect of abrocitinib on these parameters at supratherapeutic concentrations, 36 healthy volunteers received single doses of abrocitinib 600 mg, placebo, and moxifloxacin 400 mg in a 3-period crossover study. The relationship between change from baseline in Fridericia-corrected QTc (∆QTcF) values and abrocitinib plasma concentrations was modeled using a prespecified linear mixed-effects model. The 90%CIs for time-matched placebo-corrected ∆QTcF (∆∆QTcF) were calculated from model parameter estimates and assessed against the regulatory threshold (10 millisecond) at the predicted supratherapeutic concentration in patients with atopic dermatitis (2156 ng/mL). Mean (90%CI) time-matched placebo-corrected change from baseline in HR (∆∆HR) was calculated similarly. At the supratherapeutic concentration, mean (90%CI) estimates for ∆∆QTcF and ∆∆HR were 6.00 (4.52-7.49) milliseconds and 6.51 (5.23-7.80) bpm, respectively. Despite a concentration-dependent effect on ∆QTcF and ∆HR, with statistically significant slopes (90%CI) of 0.0026 (0.0018-0.0035) milliseconds/(ng/mL) and 0.0031 (0.0024-0.0038) bpm/(ng/mL), respectively, abrocitinib does not have a clinically significant effect on QTc interval or HR at supratherapeutic exposures.
Topics: Cross-Over Studies; Dermatitis, Atopic; Electrocardiography; Healthy Volunteers; Humans; Pyrimidines; Sulfonamides
PubMed: 35532896
DOI: 10.1002/cpdd.1111 -
Nature Communications May 2024Organic ultralong room-temperature phosphorescence (RTP) usually emerges instantly and immediately decays after excitation removal. Here we report a new delayed RTP that...
Organic ultralong room-temperature phosphorescence (RTP) usually emerges instantly and immediately decays after excitation removal. Here we report a new delayed RTP that is postponed by dozens of milliseconds after excitation removal and decays in two steps including an initial increase in intensity followed by subsequent decrease in intensity. The delayed RTP is achieved through introduction of phosphines into carbazole emitters. In contrast to the rapid energy transfer from single-molecular triplet states (T) to stabilized triplet states (T*) of instant RTP systems, phosphine groups insert their intermediate states (T) between carbazole-originated T and T* of carbazole-phosphine hybrids. In addition to markedly increasing emission lifetimes by ten folds, since T → T* transition require >30 milliseconds, RTP is thereby postponed by dozens of milliseconds. The emission character of carbazole-phosphine hybrids can be used to reveal information through combining instant and delayed RTP, realizing multi-level time resolution for advanced information, biological and optoelectronic applications.
PubMed: 38697970
DOI: 10.1038/s41467-024-47888-z -
Journal of Magnetic Resonance Imaging :... Oct 2021Visualization of aortic valve dynamics is important in diagnosing valvular diseases but is challenging to perform with magnetic resonance imaging (MRI) due to the...
BACKGROUND
Visualization of aortic valve dynamics is important in diagnosing valvular diseases but is challenging to perform with magnetic resonance imaging (MRI) due to the limited temporal resolution.
PURPOSE
To develop an MRI technique with sub-millisecond temporal resolution and demonstrate its application in visualizing rapid aortic valve opening and closing in human subjects in comparison with echocardiography and conventional MRI techniques.
STUDY TYPE
Prospective.
POPULATION
Twelve healthy subjects.
FIELD STRENGTH/SEQUENCE
3 T; gradient-echo-train-based sub-millisecond periodic event encoded imaging (get-SPEEDI) and balanced steady-state free precession (bSSFP).
ASSESSMENT
Images were acquired using get-SPEEDI with a temporal resolution of 0.6 msec. get-SPEEDI was triggered by an electrocardiogram so that each echo in the gradient echo train corresponded to an image at a specific time point, providing a time-resolved characterization of aortic valve dynamics. For comparison, bSSFP was also employed with 12 msec and 24 msec temporal resolutions, respectively. The durations of the aortic valve rapid opening (T ), rapid closing (T ), and the maximal aortic valve area (AVA) normalized to height were measured with all three temporal resolutions. M-mode echocardiograms with a temporal resolution of 0.8 msec were obtained for further comparison.
STATISTICAL TEST
Parameters were compared between the three sequences, together with the echocardiography results, with a Mann-Whitney U test.
RESULTS
Significantly shorter T (mean ± SD: 27.5 ± 6.7 msec) and T (43.8 ± 11.6 msec) and larger maximal AVA/height (2.01 ± 0.29 cm /m) were measured with get-SPEEDI compared to either bSSFP sequence (T of 56.3 ± 18.8 and 63.8 ± 20.2 msec; T of 68.2 ± 16.6 and 72.8 ± 18.2 msec; maximal AVA/height of 1.63 ± 0.28 and 1.65 ± 0.32 cm /m for 12 msec and 24 msec temporal resolutions, respectively, P < 0.05). In addition, the get-SPEEDI results were more consistent with those measured using echocardiography, especially for T (29.0 ± 4.1 msec, P = 0.79) and T (41.6 ± 4.3 msec, P = 0.16). DATA CONCLUSION: get-SPEEDI allows for visualization of human aortic valve dynamics and provided values closer to those measured using echocardiography than the bSSFP sequences.
LEVEL OF EVIDENCE
1 TECHNICAL EFFICACY STAGE: 1.
Topics: Aortic Valve; Aortic Valve Stenosis; Echocardiography; Humans; Magnetic Resonance Imaging; Prospective Studies
PubMed: 33761166
DOI: 10.1002/jmri.27603 -
Frontiers in Neuroscience 2020Adhesive surface electrodes are worthwhile to explore in detail as alternative to subcutaneous needle electrodes to assess myogenic evoked potentials (MEP) in human and...
Extramuscular Recording of Spontaneous EMG Activity and Transcranial Electrical Elicited Motor Potentials in Horses: Characteristics of Different Subcutaneous and Surface Electrode Types and Practical Guidelines.
INTRODUCTION
Adhesive surface electrodes are worthwhile to explore in detail as alternative to subcutaneous needle electrodes to assess myogenic evoked potentials (MEP) in human and horses. Extramuscular characteristics of both electrode types and different brands are compared in simultaneous recordings by also considering electrode impedances and background noise under not mechanically secured (not taped) and taped conditions.
METHODS
In five ataxic and one non-ataxic horses, transcranial electrical MEPs, myographic activity, and noise were simultaneously recorded from subcutaneous needle (three brands) together with pre-gelled surface electrodes (five brands) on four extremities. In three horses, the impedances of four adjacent-placed surface-electrode pairs of different brands were measured and compared. The similarity between needle and surface EMGs was assessed by cross-correlation functions, pairwise comparison of motor latency times (MLT), and amplitudes. The influence of electrode noise and impedance on the signal quality was assessed by a failure rate (FR) function. Geometric means and impedance ranges under not taped and taped conditions were derived for each brand.
RESULTS
High coherencies between EMGs of needle-surface pairs degraded to 0.7 at moderate and disappeared at strong noise. MLTs showed sub-millisecond simultaneous differences while sequential variations were several milliseconds. Subcutaneous MEP amplitudes were somewhat lower than epidermal. The impedances of subcutaneous needle electrodes were below 900 Ω and FR = 0. For four brands, the FR for surface electrodes was between 0 and 80% and declined to below 25% after taping. A remaining brand (27G DSN2260 Medtronic) revealed impedances over 100 kΩ and FR = 100% under not taped and taped conditions.
CONCLUSION
Subcutaneous needle and surface electrodes yield highly coherent EMGs and TES-MEP signals. When taped and allowing sufficient settling time, adhesive surface-electrode signals may approach the signal quality of subcutaneous needle electrodes but still depend on unpredictable conditions of the skin. The study provides a new valuable practical guidance for selection of extramuscular EMG electrodes. This study on horses shares common principles for the choice of adhesive surface or sc needle electrodes in human applications such as in intraoperative neurophysiological monitoring of motor functions of the brain and spinal cord.
PubMed: 32765207
DOI: 10.3389/fnins.2020.00652 -
JAMA Network Open Apr 2021Critical illness, a marked inflammatory response, and viruses such as SARS-CoV-2 may prolong corrected QT interval (QTc).
IMPORTANCE
Critical illness, a marked inflammatory response, and viruses such as SARS-CoV-2 may prolong corrected QT interval (QTc).
OBJECTIVE
To evaluate baseline QTc interval on 12-lead electrocardiograms (ECGs) and ensuing changes among patients with and without COVID-19.
DESIGN, SETTING, AND PARTICIPANTS
This cohort study included 3050 patients aged 18 years and older who underwent SARS-CoV-2 testing and had ECGs at Columbia University Irving Medical Center from March 1 through May 1, 2020. Patients were analyzed by treatment group over 5 days, as follows: hydroxychloroquine with azithromycin, hydroxychloroquine alone, azithromycin alone, and neither hydroxychloroquine nor azithromycin. ECGs were manually analyzed by electrophysiologists masked to COVID-19 status. Multivariable modeling evaluated clinical associations with QTc prolongation from baseline.
EXPOSURES
COVID-19, hydroxychloroquine, azithromycin.
MAIN OUTCOMES AND MEASURES
Mean QTc prolongation, percentage of patients with QTc of 500 milliseconds or greater.
RESULTS
A total of 965 patients had more than 2 ECGs and were included in the study, with 561 (58.1%) men, 198 (26.2%) Black patients, and 191 (19.8%) aged 80 years and older. There were 733 patients (76.0%) with COVID-19 and 232 patients (24.0%) without COVID-19. COVID-19 infection was associated with significant mean QTc prolongation from baseline by both 5-day and 2-day multivariable models (5-day, patients with COVID-19: 20.81 [95% CI, 15.29 to 26.33] milliseconds; P < .001; patients without COVID-19: -2.01 [95% CI, -17.31 to 21.32] milliseconds; P = .93; 2-day, patients with COVID-19: 17.40 [95% CI, 12.65 to 22.16] milliseconds; P < .001; patients without COVID-19: 0.11 [95% CI, -12.60 to 12.81] milliseconds; P = .99). COVID-19 infection was independently associated with a modeled mean 27.32 (95% CI, 4.63-43.21) millisecond increase in QTc at 5 days compared with COVID-19-negative status (mean QTc, with COVID-19: 450.45 [95% CI, 441.6 to 459.3] milliseconds; without COVID-19: 423.13 [95% CI, 403.25 to 443.01] milliseconds; P = .01). More patients with COVID-19 not receiving hydroxychloroquine and azithromycin had QTc of 500 milliseconds or greater compared with patients without COVID-19 (34 of 136 [25.0%] vs 17 of 158 [10.8%], P = .002). Multivariable analysis revealed that age 80 years and older compared with those younger than 50 years (mean difference in QTc, 11.91 [SE, 4.69; 95% CI, 2.73 to 21.09]; P = .01), severe chronic kidney disease compared with no chronic kidney disease (mean difference in QTc, 12.20 [SE, 5.26; 95% CI, 1.89 to 22.51; P = .02]), elevated high-sensitivity troponin levels (mean difference in QTc, 5.05 [SE, 1.19; 95% CI, 2.72 to 7.38]; P < .001), and elevated lactate dehydrogenase levels (mean difference in QTc, 5.31 [SE, 2.68; 95% CI, 0.06 to 10.57]; P = .04) were associated with QTc prolongation. Torsades de pointes occurred in 1 patient (0.1%) with COVID-19.
CONCLUSIONS AND RELEVANCE
In this cohort study, COVID-19 infection was independently associated with significant mean QTc prolongation at days 5 and 2 of hospitalization compared with day 0. More patients with COVID-19 had QTc of 500 milliseconds or greater compared with patients without COVID-19.
Topics: Aged, 80 and over; Anti-Infective Agents; Azithromycin; COVID-19; COVID-19 Testing; Drug Therapy, Combination; Electrocardiography; Female; Hospitalization; Humans; Hydroxychloroquine; Long QT Syndrome; Male; Middle Aged; New York; Outcome and Process Assessment, Health Care; Risk Factors; SARS-CoV-2; Time Factors; COVID-19 Drug Treatment
PubMed: 33890991
DOI: 10.1001/jamanetworkopen.2021.6842 -
BioRxiv : the Preprint Server For... Jun 2023Sleep and wake are understood to be slow, long-lasting processes that span the entire brain. Brain states correlate with many neurophysiological changes, yet the most...
Sleep and wake are understood to be slow, long-lasting processes that span the entire brain. Brain states correlate with many neurophysiological changes, yet the most robust and reliable signature of state is enriched in rhythms between 0.1 and 20 Hz. The possibility that the fundamental unit of brain state could be a reliable structure at the scale of milliseconds and microns has not been addressed due to the physical limits associated with oscillation-based definitions. Here, by analyzing high resolution neural activity recorded in 10 anatomically and functionally diverse regions of the murine brain over 24 h, we reveal a mechanistically distinct embedding of state in the brain. Sleep and wake states can be accurately classified from on the order of 10 to 10 ms of neuronal activity sampled from 100 μm of brain tissue. In contrast to canonical rhythms, this embedding persists above 1,000 Hz. This high frequency embedding is robust to substates and rapid events such as sharp wave ripples and cortical ON/OFF states. To ascertain whether such fast and local structure is meaningful, we leveraged our observation that individual circuits intermittently switch states independently of the rest of the brain. Brief state discontinuities in subsets of circuits correspond with brief behavioral discontinuities during both sleep and wake. Our results suggest that the fundamental unit of state in the brain is consistent with the spatial and temporal scale of neuronal computation, and that this resolution can contribute to an understanding of cognition and behavior.
PubMed: 37333381
DOI: 10.1101/2023.06.09.544399 -
The Journal of Neuroscience : the... Nov 2014Inhibitory neurons in cortical circuits play critical roles in composing spike timing and oscillatory patterns in neuronal activity. These roles in turn require coherent...
Inhibitory neurons in cortical circuits play critical roles in composing spike timing and oscillatory patterns in neuronal activity. These roles in turn require coherent activation of interneurons at different timescales. To investigate how the local circuitry provides for these activities, we applied resampled cross-correlation analyses to large-scale recordings of neuronal populations in the cornu ammonis 1 (CA1) and CA3 regions of the hippocampus of freely moving rats. Significant counts in the cross-correlation of cell pairs, relative to jittered surrogate spike-trains, allowed us to identify the effective couplings between neurons in CA1 and CA3 hippocampal regions on the timescale of milliseconds. In addition to putative excitatory and inhibitory monosynaptic connections, we uncovered prominent millisecond timescale synchrony between cell pairs, observed as peaks in the central 0 ms bin of cross-correlograms. This millisecond timescale synchrony appeared to be independent of network state, excitatory input, and γ oscillations. Moreover, it was frequently observed between cells of differing putative interneuronal type, arguing against gap junctions as the sole underlying source. Our observations corroborate recent in vitro findings suggesting that inhibition alone is sufficient to synchronize interneurons at such fast timescales. Moreover, we show that this synchronous spiking may cause stronger inhibition and rebound spiking in target neurons, pointing toward a potential function for millisecond synchrony of interneurons in shaping and affecting timing in pyramidal populations within and downstream from the circuit.
Topics: Animals; CA1 Region, Hippocampal; CA3 Region, Hippocampal; Cortical Synchronization; Gamma Rhythm; Gap Junctions; Male; Neural Inhibition; Neurons; Rats; Rats, Long-Evans; Theta Rhythm; Time Factors
PubMed: 25378164
DOI: 10.1523/JNEUROSCI.1091-14.2014