4 - NMR Spectroscopy Flashcards
Briefly, define NOESY spectroscopy
A form of 2D spectroscopy.
In NOESY, the Nuclear Overhauser cross relaxation between nuclear spins during the mixing period is used to establish the correlations. The spectrum obtained is similar to COSY, with diagonal peaks and cross peaks, however the cross peaks connect resonances from nuclei that are spatially close rather than those that are through-bond coupled to each other. NOESY spectra also contain extra axial peaks which do not provide extra information and can be eliminated through a different experiment by reversing the phase of the first pulse.[15]
One application of NOESY is in the study of large biomolecules such as in protein NMR, which can often be assigned using sequential walking.
Relate the NOESY method to FRET
The strength of the nuclear Overhauser enhancement (NOE) depends on the inverse 6th power of the distance between two nuclei
What three things does NOESY reveal that allows you to predict the folding of a final structure?
Three distance constraints (i, j and k) that provides connectivity in different regions of polypeptide. The structure can be folded predictably so that all distances are satisfied
What types of characteristic signal strengths do you expect to see with NOESY for an alpha helix?
See: contacts between Hα of residue i and:
HN of “self” (v. strong)
HN of i+1 & i+3 (strong)
HN of i+4 (medium)
HN of i+2 (weak)
What is the value of NMR for structural biology?
- High-resolution structures in (arguably) physiological conditions: buffers or crowded environments; membrane mimetic environments: detergent micelles, phospholipid bicelles; living cells!
Since δ is highly sensitive to environment, we can easily monitor structural perturbation on an atomic level!
Molecular dynamics are inherently seen by NMR (eg. observing a apoenzyme vs. a holoenzyme