Figure 7.

Cryo-EM structure of the Pv-M17 tetrameric conformation.A, tetrameric conformation of Pv-M17 adopted in the presence of 100 mM EDTA. Tetramer model was fit to calculated map using molecular dynamic flexible fitting (MDFF). The tetramer adopts a “dimer of dimers” conformation that associate via the C terminal of chains C and Y. The teal dimer is composed of chains A and C from the “front trimer” of the hexameric conformation, and the orange dimer is composed of chains X and Y from the “back trimer” of the hexameric conformation. B, proposed aromatic tetrad mediating the C-terminal interface between dimers. Tetrad consists of Trp541 and Trp542 from chain C and Y, each residue forming T-shaped interactions with two others. C, bottom view of tetramer; the flexible N-terminal loop (residues 125–151) of chains C and Y extend to associate with the neighboring chain and may help to stabilize the C-terminal interface. D, short C-terminal loops from chains C and Y (residues 396–412) extend into chains A and X, coming into close contact with the active sites of chains A and X.