Nitrogen-detected CAN and CON experiments as alternative experiments for main chain N

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Abstract Heteronuclear direct-detection experiments, which utilize the slower relaxation properties of low γ nuclei, such as 13C have recently been proposed for sequence-specific assignment and structural analyses of large, unstructured, and/or paramagnetic proteins. Here we present two novel 15N direct-detection experiments. The CAN experiment sequentially connects amide 15N resonances using 13Cα chemical shift matching, and the CON experiment connects the preceding 13C� nuclei. When starting from the same carbon polarization, the intensities of nitrogen signals detected in the CAN or CON experiments would be expected four times lower than those of carbon resonances observed in the corresponding 13C-detecting experiment, NCA-DIPAP or NCO-IPAP (Bermel et al. 2006b; Takeuchi et al. 2008). However, the disadvantage due to the lower γ is counteracted by the slower 15N transverse relaxation during detection, the possibility for more efficient decoupling in both dimensions, and relaxation optimized properties of the pulse sequences. As a result, the median S/N in the 15N observe CAN experiment is 16% higher than in the 13C observe NCA-DIPAP experiment. In addition, significantly higher sensitivity was observed for those residues that are hard to detect in the NCA-DIPAP experiment, such as Gly, Ser and residues with high-field Cα resonances. Both CAN and CON experiments are able to detect Pro resonances that would not be observed in conventional proton-detected experiments. In addition, those experiments are free from problems of incomplete deuterium-to-proton back exchange in amide positions of perdeuterated proteins expressed in D2O. Thus, these features and the superior resolution of 15N-detected experiments provide an attractive alternative for main chain assignments. The experiments are demonstrated with the small model protein GB1 at conditions simulating a 150 kDa protein, and the 52 kDa glutathione S-transferase dimer, GST.

• Content Type Journal Article
• DOI 10.1007/s10858-010-9430-z
• Authors
  • Koh Takeuchi, Harvard Medical School Department of Biochemistry and Molecular Pharmacology 240 Longwood Avenue Boston MA 02115 USA
  • Gregory Heffron, Harvard Medical School Department of Biochemistry and Molecular Pharmacology 240 Longwood Avenue Boston MA 02115 USA
  • Zhen-Yu J. Sun, Harvard Medical School Department of Biochemistry and Molecular Pharmacology 240 Longwood Avenue Boston MA 02115 USA
  • Dominique P. Frueh, Harvard Medical School Department of Biochemistry and Molecular Pharmacology 240 Longwood Avenue Boston MA 02115 USA
  • Gerhard Wagner, Harvard Medical School Department of Biochemistry and Molecular Pharmacology 240 Longwood Avenue Boston MA 02115 USA

• • Journal Journal of Biomolecular NMR
  • Online ISSN 1573-5001
  • Print ISSN 0925-2738
  • Journal Volume Volume 47
  • Journal Issue Volume 47, Number 4

Source: Journal of Biomolecular NMR