Intermolecular Alignment in Beta 2-Microglobulin Amyloid Fibrils

Abstract

The deposition of amyloid-like fibrils, composed primarily of the 99-residue protein β2-microglobulin (β2m), is one of the characteristic symptoms of dialysis-related amyloidosis. Fibrils formed in vitro at low pH and low salt concentration share many properties with the disease related fibrils and have been extensively studied by a number of biochemical and biophysical methods. These fibrils contain a significant β-sheet core and have a complex cryoEM electron density profile. Here, we investigate the intrasheet arrangement of the fibrils by means of [superscript 15]N−[superscript 13]C MAS NMR correlation spectroscopy. We utilize a fibril sample grown from a 50:50 mixture of [superscript 15]N,[superscript 12]C- and [superscript 14]N,[superscript 13]C-labeled β2m monomers, the latter prepared using 2-[superscript 13]C glycerol as the carbon source. Together with the use of ZF-TEDOR mixing, this sample allowed us to observe intermolecular [superscript 15]N−[superscript 13]C backbone-to-backbone contacts with excellent resolution and good sensitivity. The results are consistent with a parallel, in-register arrangement of the protein subunits in the fibrils and suggest that a significant structural reorganization occurs from the native to the fibril state.