{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,17]],"date-time":"2026-10-17T02:52:53Z","timestamp":1792205573345,"version":"4.4.0"},"reference-count":38,"publisher":"American Society for Microbiology","issue":"9","license":[{"start":{"date-parts":[[2025,9,10]],"date-time":"2025-09-10T00:00:00Z","timestamp":1757462400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2025,9,10]],"date-time":"2025-09-10T00:00:00Z","timestamp":1757462400000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/journals.asm.org\/non-commercial-tdm-license"}],"funder":[{"DOI":"10.13039\/100000072","name":"National Institute of Dental and Craniofacial Research","doi-asserted-by":"publisher","award":["R01DE033452"],"award-info":[{"award-number":["R01DE033452"]}],"id":[{"id":"10.13039\/100000072","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000057","name":"National Institute of General Medical Sciences","doi-asserted-by":"publisher","award":["R35GM138301"],"award-info":[{"award-number":["R35GM138301"]}],"id":[{"id":"10.13039\/100000057","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001665","name":"Agence Nationale de la Recherche","doi-asserted-by":"publisher","award":["ANR-15-CE11-0019,ANR-20-CE11-0011"],"award-info":[{"award-number":["ANR-15-CE11-0019,ANR-20-CE11-0011"]}],"id":[{"id":"10.13039\/501100001665","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100002915","name":"Fondation pour la Recherche M\u00e9dicale","doi-asserted-by":"publisher","award":["EQU202403018010"],"award-info":[{"award-number":["EQU202403018010"]}],"id":[{"id":"10.13039\/501100002915","id-type":"DOI","asserted-by":"publisher"}]},{"name":"A*Midex","award":["A-M-AAP-ID-17-33-170301-07.22"],"award-info":[{"award-number":["A-M-AAP-ID-17-33-170301-07.22"]}]}],"content-domain":{"domain":["journals.asm.org"],"crossmark-restriction":true},"short-container-title":["mBio"],"published-print":{"date-parts":[[2025,9,10]]},"abstract":"<jats:title>ABSTRACT<\/jats:title>\n                  <jats:sec>\n                    <jats:title\/>\n                    <jats:p>\n                      The type IX secretion system (T9SS) is a protein secretion machinery unique to the Bacteroidetes-Chlorobi-Fibrobacteres superphylum, which plays crucial roles in bacterial pathogenesis and gliding motility. It is composed of &gt;15 proteins, including the proton-motive force-dependent PorLM motor, the PorKN ring anchored to the outer membrane, and the Sov translocon. Here, we present the cryo-electron microscopy (EM) structure of the PorKN ring complex from\n                      <jats:italic toggle=\"yes\">Porphyromonas gingivalis<\/jats:italic>\n                      at 3.2 \u00c5 resolution. Our structural analysis reveals that PorK contains a repurposed formylglycine-generating enzyme-like fold, which serves as a structural hub for complex assembly rather than enzymatic activity. The complex exhibits a 33-fold symmetry with PorK and PorN assembling two tightly packed and wedged subrings. The structure reveals previously uncharacterized N- and C-terminal helices in PorN that are crucial for PorK binding and complex stability. By combining our high-resolution structure with\n                      <jats:italic toggle=\"yes\">in situ<\/jats:italic>\n                      cryo-electron tomography data, we propose a mechanism whereby PorKN undergoes conformational changes during substrate transport, transitioning between 50\u00b0 and 90\u00b0 states relative to the membrane plane. Finally, structural predictions coupled to site-directed disulfide cross-linking identified contacts between PorM and the PorKN ring. Collectively, these findings provide crucial insights into the molecular architecture and dynamic behavior of the T9SS machinery, advancing our understanding of bacterial protein secretion mechanisms.\n                    <\/jats:p>\n                    <jats:sec>\n                      <jats:title>IMPORTANCE<\/jats:title>\n                      <jats:p>\n                        The bacterial type IX secretion system (T9SS) is essential for processes such as gliding motility and secretion of virulence factors. In\n                        <jats:italic toggle=\"yes\">Porphyromonas gingivalis<\/jats:italic>\n                        , a major periodontal pathogen, the T9SS transports over 30 virulence-associated proteins, making it central to disease development. The T9SS core is composed of PorLM motors that are thought to energize the PorKN outer membrane-associated ring. However, the molecular architecture of the PorKN ring has remained unresolved. Here, we present its atomic-resolution cryo-EM structure, revealing a formylglycine-generating enzyme-like fold in PorK that mediates PorK-PorN interactions through specific insertion motifs. Our results show that the ring exhibits intrinsic structural plasticity, including dynamic flexibility and variable stoichiometry. AlphaFold models and disulfide cross-linking experiments further provide information on how PorLM motors are connected to the PorKN ring. These insights redefine our understanding of the T9SS mechanism of action and offer a structural framework for the development of targeted antimicrobial strategies.\n                      <\/jats:p>\n                    <\/jats:sec>\n                  <\/jats:sec>","DOI":"10.1128\/mbio.01799-25","type":"journal-article","created":{"date-parts":[[2025,8,7]],"date-time":"2025-08-07T13:01:02Z","timestamp":1754571662000},"update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":2,"title":["Structure of the T9SS PorKN ring complex reveals conformational plasticity based on the repurposed FGE fold"],"prefix":"10.1128","volume":"16","author":[{"given":"Xiangan","family":"Liu","sequence":"first","affiliation":[{"name":"Department of Microbiology and Molecular Genetics, McGovern Medical School","place":["Houston, USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"John D.","family":"Perpich","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/01ckdn478","id-type":"ROR","asserted-by":"publisher"}],"name":"Department of Oral Immunology and Infectious Diseases, University of Louisville","place":["Louisville, USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Liqiang","family":"Song","sequence":"additional","affiliation":[{"name":"Department of Microbiology and Molecular Genetics, McGovern Medical School","place":["Houston, USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5502-4729","authenticated-orcid":true,"given":"Christian","family":"Cambillau","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/035xkbk20","id-type":"ROR","asserted-by":"publisher"}],"name":"Laboratoire d\u2019Ing\u00e9nierie des Syst\u00e8mes Macromol\u00e9culaires (LISM, UMR7255), Aix-Marseille Universit\u00e9, CNRS","place":["Marseille, France"]},{"id":[{"id":"https:\/\/ror.org\/03265fv13","id-type":"ROR","asserted-by":"publisher"}],"name":"School of Microbiology and APC Microbiome Ireland, University College Cork","place":["Cork, Ireland"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Thierry","family":"Doan","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/035xkbk20","id-type":"ROR","asserted-by":"publisher"}],"name":"Laboratoire d\u2019Ing\u00e9nierie des Syst\u00e8mes Macromol\u00e9culaires (LISM, UMR7255), Aix-Marseille Universit\u00e9, CNRS","place":["Marseille, France"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lei","family":"Zheng","sequence":"additional","affiliation":[{"name":"Department of Biochemistry, McGovern Medical School","place":["Houston, USA"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3147-5039","authenticated-orcid":true,"given":"Richard 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AlphaFold2 predicted structures of the Porphyromonas gingivalis T9SS components complexes: dimer of PorK-PorN ring of PorK-PorN PorM dimer with PorL pentamer PorKN in complex with a dimer of PorM domains 2-4. 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