Fig. 4: Cryo-EM reconstructions of Falcilysin in the presence and absence of MK-4815.

A Raw micrograph and 2D classes of free FLN particles. B Raw micrograph and 2D classes of MK-4815-treated FLN particles. C Falcilysin 3D reconstructions in the absence of MK-4815. A majority of FLN particles are in the open conformation, and a minority are in the partially closed (“pC”) conformation. FLN structures are colored in “rainbow colors” from N- (blue) to C-terminal end (red), with transparent cryo-EM electron density maps overlaid. D Falcilysin 3D reconstructions in the presence of MK-4815. A majority of FLN particles adopt the partially closed conformation (“pC”), and a minority in the open conformation. Cryo-EM electron density map for FLN preincubated with MK-4815 are displayed at 3σ (lower panels). In the open conformation, fitting MK-4815 resulted in too close contact with the side chain of I513 and L514. Moreover, the map at position MK-4815 is weak, suggesting only very low occupancy. In the partially closed conformation, MK-4815 has strong density, and fitting MK-4815 introduces no steric hindrance with nearby residues. E Falcilysin open structure displayed as a molecular surface. N-half: purple, C-half: red. Linker: yellow ribbon. The dotted line depicts the hinge axis between N-half and C-half. F Superimposition of the partially closed conformation (“pC” obtained in the cryo-EM reconstructions) and the closed conformation (“C1” obtained using X-ray crystallography with the α-peptide). The overlay is based on C-halves. N-halves are shown as molecular surfaces. Linkers and C-halves are shown as ribbons. When in its “pC” state, FLN adopts a slightly more open conformation than in the “C1” state (please see text).