Strand-exchange assembly mechanism (IMAGE)
Caption
Mfa filaments form in a process called strand-exchange assembly. Each subunit has two ends, known as the N-terminal (NTD) and C-terminal (CTD) regions. When the N-terminal region of Mfa1 is cleaved by a protease enzyme (depicted here as Rgp), a conformational change is triggered in the C-terminal, exposing a hydrophobic groove. Neighboring filaments insert themselves into this groove, linking the molecules together. Repetition of this reaction produces the mature Mfa filament, shown on the right of the diagram. Because a similar mechanism occurs in Fim pili, this appears to be a universal assembly principle of this type of filament.
Credit
From Shibata, S., Matsunami, H., Ouhara, K. et al. Cryo-EM structure of the native assembled Mfa type V pilus from the periodontal pathogen Porphyromonas gingivalis. Commun Biol (2026). https://doi.org/10.1038/s42003-026-10515-2
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