Conformational dependence of 13C shielding and coupling constants for methionine methyl groups

Glenn L. Butterfoss, Eugene F. Derose, Scott A. Gabel, Lalith Perera, Joseph M. Krahn, Geoffrey A. Mueller, Xunhai Zheng, Robert E. London

Research output: Contribution to journalArticlepeer-review

Abstract

Methionine residues fulfill a broad range of roles in protein function related to conformational plasticity, ligand binding, and sensing/mediating the effects of oxidative stress. A high degree of internal mobility, intrinsic detection sensitivity of the methyl group, and low copy number have made methionine labeling a popular approach for NMR investigation of selectively labeled protein macromolecules. However, selective labeling approaches are subject to more limited information content. In order to optimize the information available from such studies, we have performed DFT calculations on model systems to evaluate the conformational dependence of 3 J CSCC, 3 J CSCH, and the isotropic shielding, σiso. Results have been compared with experimental data reported in the literature, as well as data obtained on [methyl- 13C]methionine and on model compounds. These studies indicate that relative to oxygen, the presence of the sulfur atom in the coupling pathway results in a significantly smaller coupling constant, 3 J CSCC/3 J COCC ~ 0.7. It is further demonstrated that the 3 J CSCH coupling constant depends primarily on the subtended CSCH dihedral angle, and secondarily on the CSCC dihedral angle. Comparison of theoretical shielding calculations with the experimental shift range of the methyl group for methionine residues in proteins supports the conclusion that the intra-residue conformationally-dependent shift perturbation is the dominant determinant of δ13Cε. Analysis of calmodulin data based on these calculations indicates that several residues adopt non-standard rotamers characterized by very large ~100° χ3 values. The utility of the δ13Cε as a basis for estimating the gauche/trans ratio for χ3 is evaluated, and physical and technical factors that limit the accuracy of both the NMR and crystallographic analyses are discussed.

Original languageEnglish (US)
Pages (from-to)31-47
Number of pages17
JournalJournal of Biomolecular NMR
Volume48
Issue number1
DOIs
StatePublished - Sep 2010

Keywords

  • Calmodulin
  • J
  • Karplus relation
  • Methionine
  • NMR
  • Scalar coupling constants
  • [methyl-C] methionine

ASJC Scopus subject areas

  • Biochemistry
  • Spectroscopy

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