3D HSQC-TOCSY-NOESY-HSQC NMR Experiment

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3D HSQC-TOCSY-NOESY-HSQC experiment [1] designed for ¹⁵N labeled proteins with poor dispersion of ¹H chemical shifts and correlates chemical shifts of amide ¹⁵N with those of ¹H and ¹⁵N atoms of nearby (most often sequential residue's) amide group.

Coherence follows the following pathway: H¹⁵N -- inept --> H¹⁵N (ω1) -- inept --> H¹⁵N -- TOCSY --> H_α -- NOE --> H¹⁵N -- inept --> H¹⁵N (ω2) -- inept --> H (ω3)¹⁵N

Two of the three dimensions record ¹⁵N chemical shift which can still be well dispersed when ¹H chemical shift is not. HSQC-TOCSY-NOESY-HSQC works best with β-sheet proteins where TOCSY transfer H-N-Ca-Ha is more efficient.

Zhang et. al [1] used this experiment to aid sequential assigment of partially unfolded state of 59-residue drk SH3 domain. About 40% of residues of those that displayed sequential connectivities in the folded state did so in the unfolded state. Experiment was recorded for 65 hours using 1 mM sample where protein about equally populated the folded and partially unfolded state.

References

1. Zhang, O and Kay, LE and Olivier, JP and Forman-Kay, JD. Backbone 1 H and 15 N resonance assignments of the N-terminal SH3 domain of drk in folded and unfolded states using enhanced-sensitivity pulsed field gradient NMR techniques. Journal of Biomolecular NMR 4(6):845--858, 1994. BibTeX [zhang94]