Insights into type IX secretion from PorKN cogwheel structure bound to PorG and attachment complexes

Dhana G. Gorasia (), Eric Hanssen, Manasi Mudaliyar, Craig J. Morton, Sepideh Valimehr, Christine Seers, Lianyi Zhang, Matthew T. Doyle, Debnath Ghosal, Paul D. Veith () and Eric C. Reynolds ()
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Dhana G. Gorasia: The University of Melbourne
Eric Hanssen: The University of Melbourne
Manasi Mudaliyar: The University of Melbourne
Craig J. Morton: CSIRO Biomedical Manufacturing
Sepideh Valimehr: The University of Melbourne
Christine Seers: The University of Melbourne
Lianyi Zhang: The University of Melbourne
Matthew T. Doyle: The University of Sydney
Debnath Ghosal: The University of Melbourne
Paul D. Veith: The University of Melbourne
Eric C. Reynolds: The University of Melbourne

Nature Communications, 2025, vol. 16, issue 1, 1-15

Abstract: Abstract The Type IX Secretion System exports proteins across the outer membrane (OM) of bacteria in the Bacteroidota phylum, however, the mechanistic details remain unknown. In Porphyromonas gingivalis the core components of the multi-protein complex are the Sov translocon, Attachment Complexes (PorQ, U, V, Z), PorLM molecular motors and PorKN rings. Here, we present a ~ 3.5 Å cryo-EM structure of the periplasmic rings comprising 32–33 subunits each of PorK and PorN. Additionally, we show the presence of a critical disulfide bond between PorK and the OM protein PorG that is essential for protein secretion and demonstrate that the Attachment Complexes bind to, and are localized above, the PorKN rings. Overall, each ring resembles a cogwheel with PorN forming cog-like projections that we propose engage with the PorLM motor to drive the rotation of the PorKN cogwheel together with PorG and associated Attachment Complexes, thus providing the energy to complete protein secretion and the coordinated cell surface attachment of the secreted cargo.

Date: 2025
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DOI: 10.1038/s41467-025-63163-1

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