National High Magnet Field Laboratory

Tallahassee, FL, United States

National High Magnet Field Laboratory

Tallahassee, FL, United States
SEARCH FILTERS
Time filter
Source Type

Jennings-Antipov L.D.,Harvard University | Song L.,Harvard University | Song L.,Dana-Farber Cancer Institute | Song L.,National High Magnet Field Laboratory | Collier R.J.,Harvard University
Proceedings of the National Academy of Sciences of the United States of America | Year: 2011

The protective antigen (PA) moiety of anthrax toxin forms oligomeric pores that translocate the enzymatic moieties of the toxin - lethal factor (LF) and edema factor (EF) - across the endosomal membrane of mammalian cells. Here we describe site-directed spin-labeling studies that identify interactions of LF with the prepore and pore conformations of PA. Our results reveal a direct interaction between the extreme N terminus of LF (residues 2-5) and the Φ-clamp, a structure within the lumen of the pore that catalyzes translocation. Also, consistent with a recent crystallographic model, we find that, upon binding of the translocation substrate to PA, LF helix α1 separates from helices α2 and α3 and binds in the α-clamp of PA. These interactions, together with the binding of the globular part of the N-terminal domain of LF to domain 1′ of PA, indicate that LF interacts with the PA pore at three distinct sites. Our findings elucidate the state from which translocation of LF and EF proceeds through the PA pore.


Qin H.,Florida State University | 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 Physical Chemistry B | Year: 2017

In terms of structural biology, solid-state NMR experiments and strategies have been well established for resonance assignments, leading to the determination of three-dimensional structures of insoluble membrane proteins in their native-like environment. It is also known that NMR has the unique capabilities to characterize structure-function relationships of membrane-bound biological systems beyond structural biology. Here, we report on solid-state NMR experiments and strategies for extracting functional activities on a sub-millisecond time scale. Specifically, we use the His37-labeled full length M2 (M2FL) protein of the Influenza A virus embedded in synthetic lipid bilayers as an example to characterize the proton conduction mechanism and kinetics. The integral membrane M2 protein assembles as a tetrameric bundle to form a proton-conducting channel that is activated by low pH and is essential for the viral lifecycle. Our results present convincing evidence for the formation of imidazolium-imidazole hydrogen bonds in the His37 tetrad at low pH and that these hydrogen bonds have a low barrier that facilitates the proton conduction mechanism in the M2FL protein. Moreover, it has been possible to measure hydronium ion exchange between water and the protons in the His37 NH bonds based on chemical exchange spectroscopy with minimized spin diffusion. The results identify an exchange rate constant of ∼4000 s-1 for pH 5.8 at -10 °C. © 2017 American Chemical Society.


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 | Year: 2016

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.


PubMed | Beijing Computational Science Research Center, National High Magnet Field Laboratory and Anhui University of Science and Technology
Type: | Journal: Journal of magnetic resonance (San Diego, Calif. : 1997) | Year: 2016

Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as (13)C 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. (13)C) and abundant I (e.g. (1)H) spins affects the measured T1S values in solid-state NMR in the absence of (1)H 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.


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 | Year: 2014

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.


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 | Year: 2012

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.


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 | Year: 2013

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.


PubMed | National High Magnet Field Laboratory and Florida State University
Type: | Journal: Journal of magnetic resonance (San Diego, Calif. : 1997) | Year: 2014

The histidine imidazole ring in proteins usually contains a mixture of three possible tautomeric states (two neutral - and 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 (15)N selectively filtered (13)C solid-state NMR spectroscopy is proposed to differentiate histidine tautomeric states and to identify all (13)C resonances of the individual imidazole rings in a mixture of tautomeric states. When (15)N selective 180 pulses are applied to the protonated or non-protonated nitrogen region, the (13)C sites that are bonded to the non-protonated or protonated nitrogen sites can be identified, respectively. A sample of (13)C, (15)N 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 and charged states from the mixture.


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 | Year: 2012

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.


Han K.,National High Magnet Field Laboratory | Toplosky V.J.,National High Magnet Field Laboratory | Xin Y.,National High Magnet Field Laboratory | Sims J.R.,Los Alamos National Laboratory | Swenson C.A.,Los Alamos National Laboratory
IEEE Transactions on Applied Superconductivity | Year: 2010

Cu matrix composites are used as conductors for pulsed magnets that have potential to reach 100 T. The conductors are fabricated by cold drawing that introduces high densities of dislocations or interfaces and internal stress. The density of the dislocation and the interface affects the mechanical properties of the conductors, such as the tensile strength and fatigue endurance at 77 K of the composites. Understanding the performance of the conductors under cyclic loading, i.e. fatigue properties, helps one to make good use of them for pulsed magnets and to manufacture conductors to meet the requirements of the magnets, particularly when the magnetic stress reaches the limit of the mechanical strength of the conductors. The goal of this research is to understand the fatigue properties of a Cu-0.085wt%Ag conductor and to relate such properties to mechanical tensile strength, dislocation densities and interface structures. The fatigue test loading is either in stress-controlled or strain-controlled mode. This work sheds a new light on the correlation between the tensile and fatigue properties at 77 K by consideration of dislocation densities and precipitate in particle strengthened conductors. © 2006 IEEE.

Loading National High Magnet Field Laboratory collaborators
Loading National High Magnet Field Laboratory collaborators