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Related Concept Videos

NMR Spectrometers: Overview01:20

NMR Spectrometers: Overview

NMR spectrometers consist of a strong magnet, a radiofrequency transmitter, and a detector attached to a computer console for recording spectra of samples containing NMR-active nuclei. In first-generation NMR instruments called continuous-wave spectrometers, the resonance frequencies of the nuclei are determined by frequency-sweep or field-sweep methods. The magnetic field strength is fixed and the rf signal is swept in the former, while the radiofrequency signal is fixed and the magnetic field...
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
2D NMR: Overview of Homonuclear Correlation Techniques01:16

2D NMR: Overview of Homonuclear Correlation Techniques

Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...
¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
NMR Spectroscopy: Chemical Shift Overview01:15

NMR Spectroscopy: Chemical Shift Overview

The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...

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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
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AssignFit: a program for simultaneous assignment and structure refinement from solid-state NMR spectra.

Ye Tian1, Charles D Schwieters, Stanley J Opella

  • 1Sanford Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, CA 92037, USA.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|November 1, 2011
PubMed
Summary
This summary is machine-generated.

AssignFit is a new program for protein structure determination using solid-state NMR. It simultaneously refines protein structures and assigns NMR restraints, improving accuracy for membrane proteins.

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Area of Science:

  • Biophysics
  • Structural Biology
  • Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

  • Solid-state NMR is crucial for determining protein structures, especially membrane proteins.
  • Assigning restraints from NMR spectra is a key challenge in structural biology.
  • Existing methods may not efficiently handle the complexity of protein structural data.

Purpose of the Study:

  • To develop and validate AssignFit, a computational tool for automated assignment and structure refinement.
  • To enable simultaneous assignment and structure refinement (SASR) using solid-state NMR orientation restraints.
  • To apply the method to challenging protein systems like integral membrane proteins.

Main Methods:

  • AssignFit utilizes dipolar coupling (DC) and chemical shift anisotropy (CSA) restraints from solid-state NMR.
  • The program minimizes differences between experimental and back-calculated NMR spectra.
  • It generates assignment permutations and refines atomic coordinates within an alignment frame.

Main Results:

  • AssignFit successfully assigned NMR restraints and refined structures for two integral membrane proteins.
  • The method demonstrated robustness for both alpha-helical and beta-barrel protein structures.
  • Simultaneous assignment and structure refinement (SASR) was achieved efficiently.

Conclusions:

  • AssignFit provides an effective approach for automated protein structure determination from solid-state NMR data.
  • The SASR method enhances the efficiency and accuracy of structural analysis for proteins.
  • This tool is particularly valuable for studying complex biological systems like membrane proteins.