30 research outputs found
Speeding-up exchange-mediated saturation transfer experiments by Fourier transform.
No full textProtein motions over various time scales are crucial for protein function. NMR relaxation dispersion experiments play a key role in explaining these motions. However, the study of slow conformational changes with lowly populated states remained elusive. The recently developed exchange-mediated saturation transfer experiments allow the detection and characterization of such motions, but require extensive measurement time. Here we show that, by making use of Fourier transform, the total acquisition time required to measure an exchange-mediated saturation transfer profile can be reduced by twofold in case that one applies linear prediction. In addition, we demonstrate that the analytical solution for R1ρ experiments can be used for fitting the exchange-mediated saturation transfer profile. Furthermore, we show that simultaneous analysis of exchange-mediated saturation transfer profiles with two different radio-frequency field strengths is required for accurate and precise characterization of the exchange process and the exchanging states
Simultaneous determination of fast and slow dynamics in molecules using extreme CPMG relaxation dispersion experiments
No full textMolecular dynamics play a significant role in how molecules perform their function. A critical method that provides information on dynamics, at the atomic level, is NMR-based relaxation dispersion (RD) experiments. RD experiments have been utilized for understanding multiple biological processes occurring at micro-to-millisecond time, such as enzyme catalysis, molecular recognition, ligand binding and protein folding. Here, we applied the recently developed high-power RD concept to the Carr-Purcell-Meiboom-Gill sequence (extreme CPMG; E-CPMG) for the simultaneous detection of fast and slow dynamics. Using a fast folding protein, gpW, we have shown that previously inaccessible kinetics can be accessed with the improved precision and efficiency of the measurement by using this experiment
Residue-specific identification of phase separation hot spots of Alzheimer's-related protein tau
No full textLiquid–liquid phase separation (LLPS) of proteins enables the formation of non-membrane-bound organelles in cells and is associated with cancer and neurodegeneration. Little is known however about the structure and dynamics of proteins in LLPS conditions, because of the polymorphic nature of liquid-like protein droplets. Using carbon-detected NMR experiments we here show that the conversion of the aggregation-prone repeat region of the Alzheimer's-related protein tau from the dispersed monomeric state to phase-separated liquid-like droplets involves tau's aggregation-prone hexapeptides and regulatory KXGS motifs. Droplet dissolution in presence of 1,6-hexanediol revealed that chemical shift perturbations in the hexapeptide motifs are temperature driven, while those in KXGS motifs report on phase separation. Residue-specific secondary structure analysis further indicated that tau's repeat region exists in extended conformation in the dispersed state and attains transient β-hairpin propensity upon LLPS. Taken together our work shows that NMR spectroscopy can provide high-resolution insights into LLPS-induced changes in intrinsically disordered proteins
High-power 1H composite pulse decoupling provides artifact free exchange-mediated saturation transfer (EST) experiments.
No full textExchange-mediated saturation transfer (EST) provides critical information regarding dynamics of molecules. In typical applications EST is studied by either scanning a wide range of (15)N chemical shift offsets where the applied (15)N irradiation field strength is on the order of hundreds of Hertz or, scanning a narrow range of (15)N chemical shift offsets where the applied (15)N irradiation field-strength is on the order of tens of Hertz during the EST period. The (1)H decoupling during the EST delay is critical as incomplete decoupling causes broadening of the EST profile, which could possibly result in inaccuracies of the extracted kinetic parameters and transverse relaxation rates. Currently two different (1)H decoupling schemes have been employed, intermittently applied 180° pulses and composite-pulse-decoupling (CPD), for situations where a wide range, or narrow range of (15)N chemical shift offsets are scanned, respectively. We show that high-power CPD provides artifact free EST experiments, which can be universally implemented regardless of the offset range or irradiation field-strengths
Effect of non-linear density temperature variation on convective heat and mass transfer flow through a porous medium in a rectangular duct with radiation chemical reaction and dissipation
No full textViscous dissipation impact on MHD free convection radiating fluid flow past a vertical porous plate
No full text
Unsteady MHD free convection flow of casson fluid over an inclined vertical plate embedded in a porous media
No full textTotal Synthesis and Stereochemical Confirmation of (−)-Olivil, (+)-Cycloolivil, (−)-Alashinols F and G, (+)-Cephafortin A, and Their Congeners: Filling in Biosynthetic Gaps
No full textFor the first time, we describe the
stereocontrolled total syntheses
of olivil, cephafortin A, 4-des-O-methyl-4-O-rhamnosyl cephafortin A, and alashinol F from a common
precursor using a combination of chemoenzymatic and biomimetic methods
for the systematic introduction of functional groups on three vicinal
stereogenic carbon atoms. We revised the previously assigned stereochemistry
of (+)-cephafortin A, which was reported as the enantiomer. Natural
and unnatural congeners provide insights into the biogenetic interrelations
of members of this family
hnCOcaNH and hncoCANH pulse sequences for rapid and unambiguous backbone assignment in (<SUP>13</SUP>C, <SUP>15</SUP>N) labeled proteins
No full textTime-saving in data acquisition is a major thrust of NMR pulse sequence development in the context of structural proteomics research. The conventional HNCA and HN(CA)CO pulse sequences, routinely used for sequential backbone assignment, have the limitation that they cannot distinguish inter- and intra-residue correlations. In order to remove this ambiguity, one has to record HNCO and HN(CO)CA or sequential HNCA experiments which provide unambiguous information of sequential correlations. However, this almost doubles the experimental time. Besides, they require repeated scanning through the 15N planes to search for the matching peaks along the carbon dimension. In this background, we present here two pulse sequences, termed as hncoCANH and hnCOcaNH that lead to spectra equivalent to HNCA and HN(CA)CO spectra, respectively, but with direct distinction of inter- and intra-residue peaks; these occur with opposite signs in the new experiments. The two pulse sequences have been derived by simple modification of the previously described HN(C)N pulse sequence [Panchal et al., J. Biomol. NMR 20 (2001) 135-147] to frequency-label 13Cα or 13C' instead of 15N during the t1 period. Like HN(C)N, these spectra also exhibit special patterns of self and sequential peaks around glycines and prolines, which enable direct identification of certain triplets of residues and thus provide internal checks during the sequential assignment walk. The spectra enable rapid and unambiguous assignment of HN, 15N and 13Cα (or 13C') in a single experiment, and thus would be of great value in high-throughput structural proteomics
