Intermolecular Alignment in β2-Microglobulin Amyloid Fibrils

The deposition of amyloid-like fibrils, composed primarily of the 99-residue protein beta(2)-microglobulin (beta(2)m), 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 beta-sheet core and have a complex cryoEM electron density profile. Here, we investigate the intrasheet arrangement of the fibrils by means of N-15-C-13 MAS NMR correlation spectroscopy. We utilize a fibril sample grown from a 50:50 mixture of N-15,C-12- and N-14,C-13-labeled beta(2)m monomers, the latter prepared using 2-C-13 glycerol as the carbon source. Together with the use of ZF-TEDOR mixing, this sample allowed us to observe intermolecular N-15-C-13 backbone-to-backbone contacts with excellent resolution and good sensitivity. The results are consistent with a parallel, in-register arrangement of the protein sub units in the fibrils and suggest that a significant structural reorganization occurs from the native to the fibril state.