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 \u3b2-D-Glcp-(1\u21926)-\u3b1-D-[6-math]-Manp-OMe dissolved in a DMSO-d6/D2O cryosolvent. The experimental NMR relaxation parameters, associated with the mathH2 probe residing at the glycosidic linkage, include math T1 and T2 and math-{math} nuclear Overhauser enhancement (NOE) as well as longitudinal and transverse dipole-dipole cross-correlated relaxation rates, acquired in the temperature range of 253\u2013293 K. These data are predicted successfully by the new theory with only the H\u2013C\u2013H angle allowed to vary. Previous attempts to fit these data using mode-decoupling models failed

Cellular Polyamines Promote Amyloid-Beta (Aβ) Peptide Fibrillation and Modulate the Aggregation Pathways

[Image: see text] The cellular polyamines spermine, spermidine, and their metabolic precursor putrescine, have long been associated with cell-growth, tumor-related gene regulations, and Alzheimer’s disease. Here, we show by in vitro spectroscopy and AFM imaging, that these molecules promote aggregation of amyloid-beta (Aβ) peptides into fibrils and modulate the aggregation pathways. NMR measurements showed that the three polyamines share a similar binding mode to monomeric Aβ(1–40) peptide. Kinetic ThT studies showed that already very low polyamine concentrations promote amyloid formation: addition of 10 μM spermine (normal intracellular concentration is ∼1 mM) significantly decreased the lag and transition times of the aggregation process. Spermidine and putrescine additions yielded similar but weaker effects. CD measurements demonstrated that the three polyamines induce different aggregation pathways, involving different forms of induced secondary structure. This is supported by AFM images showing that the three polyamines induce Aβ(1–40) aggregates with different morphologies. The results reinforce the notion that designing suitable ligands which modulate the aggregation of Aβ peptides toward minimally toxic pathways may be a possible therapeutic strategy for Alzheimer’s disease