Fig. 4

Conformational states of the MP highlighting key loop movements and H357 interactions. (a) The inset in the top left corner shows the cryo-EM structure of the MP (PDB ID: 6NM5, shown in purple) interacting with the F-pilus. The rest of panel (a) illustrates the cryo-EM experimental structure of the MP (purple cartoon) superimposed onto the “open” loop conformational state (orange cartoon), where the loop (residues L40–P50) enables H357 (shown in sticks) to interact with the F-pilus. (b) The cryo-EM experimental structure (purple cartoon) is superimposed onto the “semi-closed” loop conformational state (cyan cartoon), where the loop is in close proximity to H357, restricting its accessibility and preventing direct interaction with the F-pilus. These conformational states demonstrate the importance of “side loop” dynamics in facilitating or restricting critical interactions necessary for viral infectivity