Insights into type IX secretion from PorKN cogwheel structure bound to PorG and attachment complexes
Bibliographic record
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. Type IX secretion system (T9SS) is required for protein export in the Bacteroidota. Here, the authors obtain structure of T9SS PorKN ring which resembles a cogwheel that may have a rotational movement and is disulfide bonded to outer membrane beta-barrel PorG.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".