Model-free analysis for large proteins at high magnetic field strengths

Shou Lin Chang, Andrew P. Hinck, Rieko Ishima

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Protein backbone dynamics is often characterized using model-free analysis of three sets of 15N relaxation data: longitudinal relaxation rate (R1), transverse relaxation rate (R2), and 15N-{H} NOE values. Since the experimental data is limited, a simplified model-free spectral density function is often used that contains one Lorentzian describing overall rotational correlation but not one describing internal motion. The simplified spectral density function may be also used in estimating the overall rotational correlation time, by making the R2/ R1 largely insensitive to internal motions, as well as used as one of the choices in the model selection protocol. However, such approximation may not be valid for analysis of relaxation data of large proteins recorded at high magnetic field strengths since the contribution to longitudinal relaxation from the Lorentzian describing the overall rotational diffusion of the molecule is comparably small relative to that describing internal motion. Here, we quantitatively estimate the errors introduced by the use of the simplified spectral density in model-free analysis for large proteins at high magnetic field strength.

Original languageEnglish (US)
Pages (from-to)315-324
Number of pages10
JournalJournal of Biomolecular NMR
Issue number4
StatePublished - Aug 2007


  • Dynamics
  • NMR
  • Protein
  • Relaxation
  • Rotational correlation time

ASJC Scopus subject areas

  • Biochemistry
  • Spectroscopy


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