Fig. 6: A molecular model of the Kil pilus.

a The KilP pilus is a left-handed three-start helix with a diameter of ~46 Å and a helical rise of ~16 Å. Its extremity is constituted of a heterotrimer of minor pilins (here Tip4) and a Tip adapter (here KilK). b Remarkably, the α2 helical region of KilP (highlighted in orange) unfolds within the pilin polymer, exposing charged residues that confer electrostatic surface properties to the pilus (red: negatively charged; blue: positively charged). c AlphaFold3 structure predictions of the KilP pilus (in green) interacting with the four different Tips (in light gray) and one “adapter” pilin (KilK in blue or KilO in magenta). The “zoomed-in” view corresponds to the region of interaction between Tip4 and the KilP pilus. For clarity, it only shows the α1N-bundle (in gray) surrounded by multiple copies of KilP (in green) and one copy of KilK (in blue). A cartoon representation of the different α-helices constituting the junction between Tip4 and the pilus extremity is also provided below (see Supplementary Fig. 20 for more details). To generate these AlphaFold predictions, the leader peptide regions were systematically removed from the major and minor pilin amino acid sequences.