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Fast methionine-based solution structure determination of calcium-calmodulin complexes


Abstract Here we present a novel NMR method for the structure determination of calcium-calmodulin (Ca2+-CaM)-peptide complexes from a limited set of experimental restraints. A comparison of solved CaM-peptide structures reveals invariability in CaMâ??s backbone conformation and a structural plasticity in CaMâ??s domain orientation enabled by a flexible linker. Knowing this, the collection and analysis of an extensive set of NOESY spectra is redundant. Although RDCs can define CaM domain orientation in the complex, they lack the translational information required to position the domains on the bound peptide and highlight the necessity of intermolecular NOEs. Here we employ a specific isotope labeling strategy in which the role of methionine in CaM-peptide interactions is exploited to collect these critical NOEs. By 1H, 13C-labeling the methyl groups of deuterated methionine against a 2H, 12C background, we can acquire a 13C-edited NOESY characterized by simplified, easily analyzable spectra. Together with measured CaM backbone HN-N RDCs and intrapeptide NOE-based distances, these intermolecular NOEs provide restraints for a low temperature torsion-angle dynamics and simulated annealing protocol used to calculate the complex structure. We have applied our method to a CaM complex previously solved through X-ray crystallography: Ca2+-CaM bound to the CaM kinase I peptide (PDB code: 1MXE). The resulting structure has a backbone RMSD of 1.6 Ã? to that previously published. We have also used this test complex to investigate the importance of homologous model selection on the calculated outcome. In addition to having application for fast complex structure determination, this method can be used to determine the structures of difficult complexes characterized by chemical shift overlap and broad signals for which the traditional method based on the use of fully 13C, 15N-labeled CaM fails.

• Content Type Journal Article
• Pages 1-11
• DOI 10.1007/s10858-011-9495-3
• Authors
  • Jessica L. Gifford, Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
  • Hiroaki Ishida, Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
  • Hans J. Vogel, Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada

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

Source: Journal of Biomolecular NMR