Quantitative comparison of errors in 15N transverse relaxation rates measured using various CPMG phasing schemes
 

Quantitative comparison of errors in 15N transverse relaxation rates measured using various CPMG phasing schemes


Abstract Nitrogen-15 Carr-Purcell-Meiboom-Gill (CPMG) transverse relaxation experiment are widely used to characterize protein backbone dynamics and chemical exchange parameters. Although an accurate value of the transverse relaxation rate, R2, is needed for accurate characterization of dynamics, the uncertainty in the R2 value depends on the experimental settings and the details of the data analysis itself. Here, we present an analysis of the impact of CPMG pulse phase alternation on the accuracy of the 15N CPMG R2. Our simulations show that R2 can be obtained accurately for a relatively wide spectral width, either using the conventional phase cycle or using phase alternation when the r.f. pulse power is accurately calibrated. However, when the r.f. pulse is miscalibrated, the conventional CPMG experiment exhibits more significant uncertainties in R2 caused by the off-resonance effect than does the phase alternation experiment. Our experiments show that this effect becomes manifest under the circumstance that the systematic error exceeds that arising from experimental noise. Furthermore, our results provide the means to estimate practical parameter settings that yield accurate values of 15N transverse relaxation rates in the both CPMG experiments.

• Content Type Journal Article
• Category Article
• Pages 1-11
• DOI 10.1007/s10858-012-9621-x
• Authors
  • Wazo Myint, Department of Structural Biology, University of Pittsburgh School of Medicine, Rm 1037, Biomedical Science Tower 3, 3501 Fifth Avenue, Pittsburgh, PA 15260, USA
  • Yufeng Cai, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA
  • Celia A. Schiffer, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA
  • Rieko Ishima, Department of Structural Biology, University of Pittsburgh School of Medicine, Rm 1037, Biomedical Science Tower 3, 3501 Fifth Avenue, Pittsburgh, PA 15260, USA

• • Journal Journal of Biomolecular NMR
  • Online ISSN 1573-5001
  • Print ISSN 0925-2738

Source: Journal of Biomolecular NMR