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Sign determination of dipolar couplings in field-oriented bicelles by variable angle sample spinning (VASS).
F Tian1, J A Losonczi, M W Fischer
1Complex Carbohydrate Research Center, University of Georgia, Athens 30602-4712, USA.
Journal of Biomolecular NMR
|December 22, 1999
Summary
Variable angle sample spinning (VASS) resolves sign ambiguities in residual dipolar couplings for NMR studies. This technique allows determination of dipolar coupling signs in oriented bicelles, crucial for biomolecular structure determination.
Area of Science:
- Biomolecular NMR Spectroscopy
- Structural Biology
- Solid-State NMR
Background:
- Residual dipolar couplings (RDCs) are vital NMR constraints for biomolecular structure.
- Determining the sign of dipolar couplings is challenging, especially in solid-state NMR where they often exceed scalar couplings.
Purpose of the Study:
- To resolve sign ambiguities of residual dipolar couplings in field-oriented bicelles.
- To investigate the director behavior of bicelles under Variable Angle Sample Spinning (VASS) conditions.
Main Methods:
- Utilized Variable Angle Sample Spinning (VASS) techniques.
- Employed 31P Nuclear Magnetic Resonance (NMR) spectroscopy.
- Studied bicelle systems including DMPC/DHPC and DMPC/CHAPSO.
Main Results:
- Identified a stable bicelle configuration at spinning angles below the magic angle (54.7°).
- Observed bicelle director distribution primarily in a plane perpendicular to the rotation axis.
- Demonstrated that dipolar interactions can be scaled to match J-coupling by adjusting the spinning angle.
Conclusions:
- VASS effectively resolves sign ambiguities in residual dipolar couplings for oriented bicelles.
- The findings enable accurate determination of the relative signs of dipolar and scalar couplings.
- This method enhances the utility of RDCs in biomolecular structure elucidation.