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Fu R.,National High Magnet Field Laboratory | Li J.,Beijing Computational Science Research Center | Cui J.,Anhui University of Science and Technology | Peng X.,Anhui University of Science and Technology
Journal of Magnetic Resonance

Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as 13C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. 13C) and abundant I (e.g. 1H) spins affects the measured T1S values in solid-state NMR in the absence of 1H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance l-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions. © 2016 Elsevier Inc. Source

Zhang Z.,CAS Wuhan Institute of Physics and Mathematics | Miao Y.,Florida State University | Miao Y.,National High Magnet Field Laboratory | Liu X.,CAS Wuhan Institute of Physics and Mathematics | And 5 more authors.
Journal of Magnetic Resonance

A sinusoidal modulation scheme is described for selective heteronuclear polarization transfer between two dilute spins in double cross polarization magic-angle-spinning nuclear magnetic resonance spectroscopy. During the second N → C cross polarization, the 13C RF amplitude is modulated sinusoidally while the 15N RF amplitude is tangent. This modulation induces an effective spin-lock field in two selective frequency bands in either side of the 13C RF carrier frequency, allowing for simultaneous polarization transfers from 15N to 13C in those two selective frequency bands. It is shown by experiments and simulations that this sinusoidal modulation allows one to selectively polarize from 15N to its covalently bonded 13Cα and 13C' carbons in neighboring peptide planes simultaneously, which is useful for establishing the backbone connectivity between two sequential residues in protein structural elucidation. The selectivity and efficiency were experimentally demonstrated on a uniformly 13C, 15N-labeled β1 immunoglobulin binding domain of protein G (GB1). © 2012 Elsevier Inc. All rights reserved. Source

Miao Y.,Florida State University | Cross T.A.,Florida State University | Cross T.A.,National High Magnet Field Laboratory | Fu R.,National High Magnet Field Laboratory
Journal of Biomolecular NMR

The feasibility of using difference spectroscopy, i.e. subtraction of two correlation spectra at different mixing times, for substantially enhanced resolution in crowded two-dimensional 13C-13C chemical shift correlation spectra is presented. With the analyses of 13C-13C spin diffusion in simple spin systems, difference spectroscopy is proposed to partially separate the spin diffusion resonances of relatively short intra-residue distances from the longer inter-residue distances, leading to a better identification of the inter-residue resonances. Here solid-state magic-angle-spinning NMR spectra of the full length M2 protein embedded in synthetic lipid bilayers have been used to illustrate the resolution enhancement in the difference spectra. The integral membrane M2 protein of Influenza A virus assembles as a tetrameric bundle to form a proton-conducting channel that is activated by low pH and is essential for the viral lifecycle. Based on known amino acid resonance assignments from amino acid specific labeled samples of truncated M2 sequences or from time-consuming 3D experiments of uniformly labeled samples, some inter-residue resonances of the full length M2 protein can be identified in the difference spectra of uniformly 13C labeled protein that are consistent with the high resolution structure of the M2 (22-62) protein (Sharma et al., Science 330(6003):509-512, 2010). © 2013 Springer Science+Business Media Dordrecht. Source

Moss C.L.,University of Washington | Chamot-Rooke J.,Ecole Polytechnique - Palaiseau | Nicol E.,Ecole Polytechnique - Palaiseau | Brown J.,Waters Corporation | And 9 more authors.
Journal of Physical Chemistry B

Infrared multiphoton dissociation (IRMPD) spectroscopy, using a free-electron laser, and ion mobility measurements, using both drift-cell and traveling-wave instruments, were used to investigate the structure of gas-phase peptide (AAHAL + 2H)2+ ions produced by electrospray ionization. The experimental data from the IRMPD spectra and collisional cross section (Ω) measurements were consistent with the respective infrared spectra and Ω calculated for the lowest-energy peptide ion conformer obtained by extensive molecular dynamics searches and combined density functional theory and ab initio geometry optimizations and energy calculations. Traveling-wave ion mobility measurements were employed to obtain the Ω of charge-reduced peptide cation-radicals, (AAHAL + 2H)+, and the c3, c4, z3, and z4 fragments from electron-transfer dissociation (ETD) of (AAHAL + 2H)2+. The experimental Ω for the ETD charge-reduced and fragment ions were consistent with the values calculated for fully optimized ion structures and indicated that the ions retained specific hydrogen bonding motifs from the precursor ion. In particular, the Ω for the doubly protonated ions and charge-reduced cation-radicals were nearly identical, indicating negligible unfolding and small secondary structure changes upon electron transfer. The experimental Ω for the (AAHAL + 2H) + cation-radicals were compatible with both zwitterionic and histidine radical structures formed by electron attachment to different sites in the precursor ion, but did not allow their distinction. The best agreement with the experimental Ω was found for ion structures fully optimized with M06-2X/6-31+G(d,p) and using both projection approximation and trajectory methods to calculate the theoretical Ω values. © 2012 American Chemical Society. Source

Miao Y.,Florida State University | Cross T.A.,Florida State University | Cross T.A.,National High Magnet Field Laboratory | Fu R.,National High Magnet Field Laboratory
Journal of Magnetic Resonance

The histidine imidazole ring in proteins usually contains a mixture of three possible tautomeric states (two neutral - τ and π states and a charged state) at physiological pHs. Differentiating the tautomeric states is critical for understanding how the histidine residue participates in many structurally and functionally important proteins. In this work, one dimensional 15N selectively filtered 13C solid-state NMR spectroscopy is proposed to differentiate histidine tautomeric states and to identify all 13C resonances of the individual imidazole rings in a mixture of tautomeric states. When 15N selective 180° pulses are applied to the protonated or non-protonated nitrogen region, the 13C sites that are bonded to the non-protonated or protonated nitrogen sites can be identified, respectively. A sample of 13C, 15N labeled histidine powder lyophilized from a solution at pH 6.3 has been used to illustrate the usefulness of this scheme by uniquely assigning resonances of the neutral τ and charged states from the mixture. © 2014 Elsevier Inc. All rights reserved. Source

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