Transverse relaxation optimized spectroscopy (TROSY) is an experiment in
protein NMR
Nuclear magnetic resonance spectroscopy of proteins (usually abbreviated protein NMR) is a field of structural biology in which NMR spectroscopy is used to obtain information about the structure and dynamics of proteins, and also nucleic acids, and ...
spectroscopy that allows studies of large molecules or complexes.
The application of
NMR
Nuclear magnetic resonance (NMR) is a physical phenomenon in which atomic nucleus, nuclei in a strong constant magnetic field are disturbed by a weak oscillating magnetic field (in the near and far field, near field) and respond by producing ...
to large molecules is normally limited by the fact that the line widths generally increase with
molecular mass
The molecular mass () is the mass of a given molecule, often expressed in units of daltons (Da). Different molecules of the same compound may have different molecular masses because they contain different isotopes of an element. The derived quan ...
. Larger molecules have longer rotational correlation times and consequently shorter transverse relaxation times (T
2). In other words, the
NMR signal from larger molecules decays more rapidly, leading to line broadening in the NMR spectrum and poor
resolution.
In an
HSQC spectrum in which
decoupling has not been applied, peaks appear as multiplets due to
J-coupling
In nuclear chemistry and nuclear physics, ''J''-couplings (also called spin-spin coupling or indirect dipole–dipole coupling) are mediated through chemical bonds connecting two spins. It is an indirect interaction between two nuclear spins tha ...
. Crucially the different multiplet components have different widths. This is due to constructive or destructive interaction between different
relaxation mechanisms. Typically for large proteins at high
magnetic field
A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...
strengths, the transverse (T
2) relaxation is dominated by the dipole-dipole (DD) mechanism and the
chemical shift
In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of ...
anisotropy (CSA) mechanism. As the relaxation mechanisms are generally correlated but contribute to the overall relaxation rate of a given component with different signs, the multiplet components relax with very different overall rates. The TROSY experiment
[K. Pervushin, R. Riek, G. Wider, and K. Wüthrich (1997). ''Attenuated T2 relaxation by mutual cancellation of dipole-dipole coupling and chemical shift anisotropy indicates an avenue to NMR structures of very large biological macromolecules in solution.'' Proc. Natl. Acad. Sci. USA 94 12366-71 ] is designed to select the component for which the different relaxation mechanisms have almost cancelled, leading to a single, sharp peak in the spectrum. This significantly increases both spectral resolution and sensitivity, both of which are at a premium when studying large and complex biomolecules.
This approach significantly extends the molecular mass range that can be studied by NMR, but it generally requires high magnetic fields to achieve the necessary balance between the CSA and DD relaxation mechanisms; CSAs scale with field strength, while
dipole-dipole couplings are field-independent.
References
Nuclear magnetic resonance experiments
{{NMR-stub