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Abstract In oriented‐sample (OS) solid‐state NMR of membrane proteins, the angular‐dependent dipolar couplings and chemical shifts provide a direct input for structure calculations. However, so far only1H–15N dipolar couplings and15N chemical shifts have been routinely assessed in oriented15N‐labeled samples. The main obstacle for extending this technique to membrane proteins of arbitrary topology has remained in the lack of additional experimental restraints. We have developed a new experimental triple‐resonance NMR technique, which was applied to uniformly doubly (15N,13C)‐labeled Pf1 coat protein in magnetically aligned DMPC/DHPC bicelles. The previously inaccessible1Hα–13Cαdipolar couplings have been measured, which make it possible to determine the torsion angles between the peptide planes without assuming α‐helical structure a priori. The fitting of three angular restraints per peptide plane and filtering by Rosetta scoring functions has yielded a consensus α‐helical transmembrane structure for Pf1 protein.
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Quantifying the effects of long-range 13C-13C dipolar coupling on measured relaxation rates in RNA
Abstract Selective stable isotope labeling has transformed structural and dynamics analysis of RNA by NMR spectroscopy. These methods can remove13C-13C dipolar couplings that complicate13C relaxation analyses. While these phenomena are well documented for sites with adjacent13C nuclei (e.g. ribose C1′), less is known about so-called isolated sites (e.g. adenosine C2). To investigate and quantify the effects of long-range (> 2 Å)13C-13C dipolar interactions on RNA dynamics, we simulated adenosine C2 relaxation rates in uniformly [U-13C/15N]-ATP or selectively [2-13C]-ATP labeled RNAs. Our simulations predict non-negligible13C-13C dipolar contributions from adenosine C4, C5, and C6 to C2 longitudinal (R1) relaxation rates in [U-13C/15N]-ATP labeled RNAs. Moreover, these contributions increase at higher magnetic fields and molecular weights to introduce discrepancies that exceed 50%. This will become increasingly important at GHz fields. Experimental R1measurements in the 61 nucleotide human hepatitis B virus encapsidation signal ε RNA labeled with [U-13C/15N]-ATP or [2-13C]-ATP corroborate these simulations. Thus, in the absence of selectively labeled samples, long-range13C-13C dipolar contributions must be explicitly taken into account when interpreting adenosine C2 R1rates in terms of motional models for large RNAs.
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- Award ID(s):
- 1808705
- PAR ID:
- 10224164
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Journal of Biomolecular NMR
- ISSN:
- 0925-2738
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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