Fig. 1
From: The structure of a β2-microglobulin fibril suggests a molecular basis for its amyloid polymorphism
MAS-NMR spectra of β2m fibrils show a single subunit structure. a Excerpt of a 2D 13C–13C MAS spectrum of uniformly [13C/15N]-labelled β2m fibrils using 15 ms PAR mixing recorded at a field strength corresponding to ω0H/2π = 900 MHz, T = 268 K, and ωr/2π = 20 kHz. τmix = 15 ms, with an 83 kHz 1H decoupling field applied during acquisition. b, c, d Cα–Cβ correlations of Ser/Thr residues in samples differentially labelled with 13C, as indicated for each plot. For each Ser and Thr only one correlation should be present in a monomorphic sample. Since β2m has 5 Thr and 9 Ser residues, a total of 14 resonances should be observed. For Ser, 6/9 expected peaks (S28, S52, S55, S57, S61, and S88) are observed. S33 is not resolved, since its Cα and Cβ chemical shifts are identical, i.e. the cross-peak overlaps with the diagonal peak. S11 is unobserved since it is part of the region of intermediate flexibility. We observed a weak peak that is not connected to any other residues and is believed to stem from S20. For threonine, 4 cross-peaks are expected (T68, T71, T73, T86), since T4 is part of the very flexible N-terminus and is not observed. However, 5 cross-peaks are observed. The cross-peak of T68 exhibits doubling, presumably reflecting local structural perturbations for different polymorphs (see main text). Grey peak designations are included as a reference for missing peaks in this spectrum or which lie below the plotting level used. These differences are a result of the different labelling schemes and mixing efficiencies
