Optimized selection of slow-relaxing 13 C transitions in methyl groups of proteins: application to relaxation dispersion

J Biomol NMR. 2020 Dec;74(12):673-680. doi: 10.1007/s10858-020-00349-3. Epub 2020 Oct 1.

Abstract

Optimized selection of the slow-relaxing components of single-quantum 13C magnetization in 13CH3 methyl groups of proteins using acute (< 90°) angle 1H radio-frequency pulses, is described. The optimal selection scheme is more relaxation-tolerant and provides sensitivity gains in comparison to the experiment where the undesired (fast-relaxing) components of 13C magnetization are simply 'filtered-out' and only 90° 1H pulses are employed for magnetization transfer to and from 13C nuclei. When applied to methyl 13C single-quantum Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiments for studies of chemical exchange, the selection of the slow-relaxing 13C transitions results in a significant decrease in intrinsic (exchange-free) transverse spin relaxation rates of all exchanging species. For exchanging systems involving high-molecular-weight species, the lower transverse relaxation rates translate into an increase in the information content of the resulting relaxation dispersion profiles.

Keywords: 13CH3 spin-system; Acute angle RF pulses; Methyl 13C CPMG relaxation dispersion; Methyl NMR.

MeSH terms

  • Carbon Isotopes / chemistry*
  • Nuclear Magnetic Resonance, Biomolecular*
  • Proteins / chemistry*
  • Thermodynamics

Substances

  • Carbon Isotopes
  • Proteins
  • Carbon-13