The Role of Rotational Motion in Diffusion NMR Experiments on Supramolecular Assemblies: Application to Sup35NM Fibrils

Abstract

Pulsed-field gradient (PFG) NMR is an important tool for characterization of biomolecules and supramolecular assemblies.H owever,f or micrometer-sized objects,s uch as amyloid fibrils,these experiments become difficult to interpret because in addition to translational diffusion they are also sensitive to rotational diffusion. We have constructed am athematical theory describing the outcome of PFG NMR experiments on rod-like fibrils.T otest its validity,wehave studied the fibrils formed by Sup35NM segment of the prion protein Sup35. The interpretation of the PFG NMR data in this system is fully consistent with the evidence from electron microscopy. Contrary to some previously expressed views,t he signals originating from disordered regions in the fibrils can be readily differentiated from the similar signals representing small soluble species (e.g.p roteolytic fragments). This paves the way for diffusion-sorted NMR experiments on complex amyloidogenic samples.