Conformational dependence of 13C shielding and coupling constants for methionine

[nmrlearner]

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, Ï?iso. 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° Ï?3 values. The utility of the δ13Cε as a basis for estimating the gauche/trans ratio for Ï?3 is evaluated, and physical and technical factors that limit the accuracy of both the NMR and crystallographic analyses are discussed.

• Content Type Journal Article
• DOI 10.1007/s10858-010-9436-6
• Authors
  • Glenn L. Butterfoss, The Courant Institute of Mathematical Sciences and the Center for Genomics and Systems Biology, New York University, New York, NY 10003, USA
  • Eugene F. DeRose, Laboratory of Structural Biology, National Institute of Environmental Health Sciences (NIEHS), NIH, MR-01, 111 T. W. Alexander Drive, Research Triangle Park, NC 27709, USA
  • Scott A. Gabel, Laboratory of Structural Biology, National Institute of Environmental Health Sciences (NIEHS), NIH, MR-01, 111 T. W. Alexander Drive, Research Triangle Park, NC 27709, USA
  • Lalith Perera, Laboratory of Structural Biology, National Institute of Environmental Health Sciences (NIEHS), NIH, MR-01, 111 T. W. Alexander Drive, Research Triangle Park, NC 27709, USA
  • Joseph M. Krahn, Laboratory of Structural Biology, National Institute of Environmental Health Sciences (NIEHS), NIH, MR-01, 111 T. W. Alexander Drive, Research Triangle Park, NC 27709, USA
  • Geoffrey A. Mueller, Laboratory of Structural Biology, National Institute of Environmental Health Sciences (NIEHS), NIH, MR-01, 111 T. W. Alexander Drive, Research Triangle Park, NC 27709, USA
  • Xunhai Zheng, Laboratory of Structural Biology, National Institute of Environmental Health Sciences (NIEHS), NIH, MR-01, 111 T. W. Alexander Drive, Research Triangle Park, NC 27709, USA
  • Robert E. London, Laboratory of Structural Biology, National Institute of Environmental Health Sciences (NIEHS), NIH, MR-01, 111 T. W. Alexander Drive, Research Triangle Park, NC 27709, USA

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

Source: Journal of Biomolecular NMR