Intermolecular Alignment in β₂-Microglobulin Amyloid Fibrils

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 ¹⁵N−¹³C MAS NMR correlation spectroscopy. We utilize a fibril sample grown from a 50:50 mixture of ¹⁵N,¹²C- and ¹⁴N,¹³C-labeled β₂m monomers, the latter prepared using 2-¹³C glycerol as the carbon source. Together with the use of ZF-TEDOR mixing, this sample allowed us to observe intermolecular ¹⁵N−¹³C 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

Superchiral Plasmonic Phase Sensitivity for Fingerprinting of Protein Interface Structure

The structure adopted by biomaterials, such as proteins, at interfaces is a crucial parameter in a range of important biological problems. It is a critical property in defining the functionality of cell/bacterial membranes and biofilms (<i>i.e.</i>, in antibiotic-resistant infections) and the exploitation of immobilized enzymes in biocatalysis. The intrinsically small quantities of materials at interfaces precludes the application of conventional spectroscopic phenomena routinely used for (bio)­structural analysis due to a lack of sensitivity. We show that the interaction of proteins with superchiral fields induces asymmetric changes in retardation phase effects of excited bright and dark modes of a chiral plasmonic nanostructure. Phase retardations are obtained by a simple procedure, which involves fitting the line shape of resonances in the reflectance spectra. These interference effects provide fingerprints that are an incisive probe of the structure of interfacial biomolecules. Using these fingerprints, layers composed of structurally related proteins with differing geometries can be discriminated. Thus, we demonstrate a powerful tool for the bioanalytical toolbox