Fig. 5.

Two models of the fluorescence-inducing binding of Thioflavin T (ThT) to an insulin fibril consisting of three intertwining protofibrils, where each protofibril has two protofilaments. a, b Binding of ThT as a dimer between the three protofibrils is illustrated on the contoured density cross section of the insulin fibril as red dots (a) and on the subunit repeat of the fibril obtained by small-angle X-ray scattering as red rectangles (b). c, d, e Binding of a ThT monomer between the protofilaments forming the protofibrils is illustrated on the contoured density cross section of the insulin fibril (c) and on the model of a protofibril consisting of two protofilaments formed by a helical oligomer (top view (d) and side view (e)). Eight ThT ions are shown stacking end-by-end (e). The length of the oligomer in the protofilament is 200 Å. Reprinted from Groenning et al. [53] with permission from Elsevier. The contoured density cross sections and the structural models of insulin fibrils were originally modified from Jimenez et al. [14]. Copyright 2002 National Academy of Sciences, USA and Vestergaard et al. [20], respectively