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Related Concept Videos

Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...
Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
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When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis. This...
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

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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...

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NMR 15N Relaxation Experiments for the Investigation of Picosecond to Nanoseconds Structural Dynamics of Proteins
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Functional dynamics of response regulators using NMR relaxation techniques.

Alexandra K Gardino1, Dorothee Kern

  • 1Department of Biochemistry, Brandeis University, Waltham, MA, USA.

Methods in Enzymology
|July 5, 2007
PubMed
Summary

Phosphorylation does not create active protein states but shifts existing equilibria. This population-shift mechanism challenges traditional views of signaling and protein activation.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Structural Biology

Background:

  • Phosphorylation-mediated signaling traditionally assumes activation involves a conformational switch to a new, active state.
  • Response regulators are key signaling proteins regulated by phosphorylation.

Purpose of the Study:

  • To investigate the activation mechanism of the response regulator NtrC using NMR spectroscopy.
  • To challenge the traditional view of phosphorylation-induced conformational changes.

Main Methods:

  • Nuclear Magnetic Resonance (NMR) relaxation experiments.
  • Analysis of chemical shift data.
  • Linking structural and functional information.

Main Results:

  • NMR data revealed kinetic, thermodynamic, and structural details of conformational exchange in NtrC.
  • Both inactive and active conformations pre-exist prior to phosphorylation.
  • Activation occurs through a shift in the equilibrium between these pre-existing states.

Conclusions:

  • The activation of NtrC follows a population-shift mechanism, not a de novo conformational change.
  • This population-shift model challenges the traditional view of phosphorylation-mediated signaling.
  • The proposed mechanism may be a general paradigm for response regulator activation and broader phosphorylation signaling.