An integrated approach to NMR spin relaxation in flexible biomolecules: application to beta-D-glucopyranosyl-(1-->6)-alpha-D-mannopyranosyl-OMe.
The description of the reorientational dynamics of flexible molecules is a challenging task, in particular when the rates of internal and global motions are comparable. The commonly used simple mode-decoupling models are based on the assumption of statistical independence between these motions. This assumption is not valid when the time scale separation between their rates is small, a situation that was found to arise in oligosaccharides in the context of certain internal motions. To make possible the interpretation of NMR spin relaxation data from such molecules, we developed a comprehensive approach generally applicable to flexible rotators with one internal degree of freedom. This approach integrates a stochastic description of coupled global tumbling and internal torsional motion, quantum chemical calculations of the local potential and the local geometry at the site of the restricted torsion, and hydrodynamics-based calculations of the diffusive properties. The method is applied to the disaccharide beta-D-Glcp-(1-->6)-alpha-D-[6-(13)C]-Manp-OMe dissolved in a DMSO-d(6)/D(2)O cryosolvent. The experimental NMR relaxation parameters, associated with the (13)CH(2) probe residing at the glycosidic linkage, include (13)C T(1) and T(2) and (13)C-{(1)H} nuclear Overhauser enhancement (NOE) as well as longitudinal and transverse dipole-dipole cross-correlated relaxation rates, acquired in the temperature range of 253-293 K. These data are predicted successfully by the new theory with only the H-C-H angle allowed to vary. Previous attempts to fit these data using mode-decoupling models failed.
Zerbetto
Mirco
M
Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Padova 35131, Italy.
Polimeno
Antonino
A
Kotsyubynskyy
Dmytro
D
Ghalebani
Leila
L
Kowalewski
Jozef
J
Meirovitch
Eva
E
Olsson
Ulrika
U
Widmalm
Göran
G
D002236:Carbohydrate Conformation; D004187:Disaccharides / Q000737:chemistry*; D005947:Glucose / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008358:Mannose / Q000737:chemistry*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D009038:Motion
D004187:Disaccharides; D005947:Glucose; D008358:Mannose