The representative conformation in Figure , calculated through 1.5 µs in aggregate simulations, reveals a bound conformation of nitrocefin, stabilized by hydrogen bonds between lysine sidechains displayed on the PFK fibrils' surface and carbonyl units in nitrocefin. Notably, the snapshot structure in Figure indicates that nitrocefin complexation occurs via hydrogen bonds between the sidechains of Lys-10 and Lys-12 and nitrocefin carbonyls. It should be noted that the MD simulations yielded bound nitrocefin conformations in which other lysine residues in the PFK sequence partook in hydrogen bond formation. Indeed, the bar diagram in Figure depicts the relative probabilities of hydrogen bond formation between nitrocefin and primary amines of the lysine residues, as predicted by the MD simulation analysis. Figure points to preferred binding of nitrocefin to the lysine residues that are close to the C-terminus, presumably due to affinity of nitrocefin to the positively charged terminus. Indeed, electrostatic interactions play an important role in the formation of biological complexes in which Brownian motion limits the rate of encounters between the assembly constituents (nitrocefin and PFK fibrils' surface in this system) Images were made with UCSF-chimera and PyMol. For more orientations see Figure . The 3D map is based on 507,432 analyzed particles.