attachment organelle

GO:0033099 · Appendage · Appendage · Proposed

A membrane-bounded polar cell extension in Mycoplasma species that concentrates cytadherence and cytoskeletal proteins for host-cell attachment, gliding motility, and organelle-linked cell division. [GO:0033099]

Synonyms: terminal organelle

Has part: attachment organelle membrane (GO:0033111)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
P1 adhesin surface complex	Protein complex	part of	Reviewed label only (reviewed name; no accession asserted)	mpn141, mpn142		DISPENSABLE	Forms the surface nap-like adhesin layer around the attachment organelle core and concentrates receptor-binding machinery at the pole. `DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 review prior localization of P1, P40, and P90 on the surface around the internal core and include them among the known organelle components. `DOI:10.1128/mBio.00243-16` Kawamoto et al. 2016 imaged the Mycoplasma pneumoniae class IV-22 mutant lacking P1/P40/P90 and surface nap but retaining the attachment-organelle membrane and internal core. DISPENSABLE refers to this assembly phenotype, not normal cytadherence or gliding, or universal dispensability across Mycoplasma.
P30 tip adhesin	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	mpn453		DISPENSABLE	Localizes to the front surface of the attachment organelle and supports cytadherence and proper polar extension development. `DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 mapped P30 to the surface of the front end of the attachment organelle. `DOI:10.1128/JB.181.4.1079-1087.1999` Romero-Arroyo et al. 1999 analyzed P30 mutants and connected P30 with cytadherence and correct cell extension morphology. `DOI:10.1111/mmi.13937` Krause et al. 2018 observed all internal attachment-organelle substructures in the M129-derived II-3 mutant lacking P30, with reduced P65 and fewer surface protein knobs. DISPENSABLE refers to organelle assembly in this mutant, not normal cytadherence, gliding or morphology, or universal dispensability across Mycoplasma.
HMW2 paired-plate scaffold	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	hmw2, mpn310	parallel molecules in the paired plates	ESSENTIAL	Acts as the length-setting internal-core scaffold of the paired plates in the polar extension. `DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 mapped HMW2 molecules along the paired plates of the internal core. `DOI:10.1371/journal.ppat.1009621` Nakane et al. 2021 engineered HMW2 coiled-coil lengths and showed HMW2 sets attachment-organelle length.
P65 terminal-button protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	p65, mpn309			Localizes to the front terminal-button substructure that caps the paired plates within the electron-dense internal core. `DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 placed P65 in the terminal-button substructure of the attachment-organelle internal core.
HMW3 terminal-button protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	hmw3, mpn452			Localizes to the terminal-button boundary with the paired plates in the electron-dense internal core. `DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 placed HMW3 at the boundary between the terminal button and the paired plates.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

HMW2 paired-plate scaffold

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P75471`	Cytadherence high molecular weight protein 2	hmw2	Mycoplasmoides pneumoniae M129 (`NCBITaxon:272634`)	REVIEWED
Role and evidence (2 references) UniProt annotates this protein to SL-0020 (attachment organelle); component role: Acts as the length-setting internal-core scaffold of the paired plates in the polar extension. `PMID:15466048` Kenri T et al. 2004, ‘Use of fluorescent-protein tagging to determine the subcellular localization of mycoplasma pneumoniae proteins encoded by the cytadherence regulatory locus.’, J Bacteriol. ECO:0000269 experimental evidence for the attachment organelle localisation of P75471, as cited by UniProt. `PMID:26633540` Nakane D et al. 2015, ‘Systematic Structural Analyses of Attachment Organelle in Mycoplasma pneumoniae.’, PLoS Pathog. ECO:0000269 experimental evidence for the attachment organelle localisation of P75471, as cited by UniProt.

P65 terminal-button protein

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0CJ81`	Proline-rich P65 protein	p65	Mycoplasmoides pneumoniae M129 (`NCBITaxon:272634`)	REVIEWED
Role and evidence (2 references) UniProt annotates this protein to SL-0020 (attachment organelle); component role: Localizes to the front terminal-button substructure that caps the paired plates within the electron-dense internal core. `PMID:15466048` Kenri T et al. 2004, ‘Use of fluorescent-protein tagging to determine the subcellular localization of mycoplasma pneumoniae proteins encoded by the cytadherence regulatory locus.’, J Bacteriol. ECO:0000269 experimental evidence for the attachment organelle localisation of P0CJ81, as cited by UniProt. `PMID:26633540` Nakane D et al. 2015, ‘Systematic Structural Analyses of Attachment Organelle in Mycoplasma pneumoniae.’, PLoS Pathog. ECO:0000269 experimental evidence for the attachment organelle localisation of P0CJ81, as cited by UniProt.

HMW3 terminal-button protein

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q50360`	Cytadherence high molecular weight protein 3	hmw3	Mycoplasmoides pneumoniae M129 (`NCBITaxon:272634`)	REVIEWED
Role and evidence (1 reference) UniProt annotates this protein to SL-0020 (attachment organelle); component role: Localizes to the terminal-button boundary with the paired plates in the electron-dense internal core. `PMID:26633540` Nakane D et al. 2015, ‘Systematic Structural Analyses of Attachment Organelle in Mycoplasma pneumoniae.’, PLoS Pathog. ECO:0000269 experimental evidence for the attachment organelle localisation of Q50360, as cited by UniProt.

Taxonomic distribution

NCBITaxon:544448 Mycoplasmatota — VARIABLE: Attachment organelles are characterized in the Mycoplasma pneumoniae cluster within Mycoplasmatota, not universally across the phylum. Chen et al. use historical Mollicutes terminology; current NCBI taxonomy places the M129 example in Mycoplasmoidales outside class Mollicutes (NCBITaxon:31969). [DOI:10.1186/s12866-025-04320-w]
NCBITaxon:2 Bacteria — RARE: The characterized attachment organelle is restricted to a small mycoplasma lineage and is not a general bacterial appendage. [DOI:10.1186/s12866-025-04320-w]

Canonical examples

NCBITaxon:272634 Mycoplasmoides pneumoniae M129 — The Nakane et al. structural mapping work used the M129 type strain, named Mycoplasma pneumoniae M129 in that literature. [DOI:10.1371/journal.ppat.1005299]

Functions

host-cell cytadherence — Polar clustering of P1-family and P30 adhesins lets cells attach to host tissue surfaces.
- DOI:10.1046/j.1365-2958.2003.03899.x Krause and Balish 2004 review the terminal organelle as the polarized structure that mediates M. pneumoniae cytadherence.
- DOI:10.1128/JB.181.4.1079-1087.1999 Romero-Arroyo et al. 1999 showed P30 is required for normal cytadherence.
attachment-organelle-dependent gliding motility — The polar protrusion supports M. pneumoniae gliding over host surfaces. Coupling of internal-core deformation to surface adhesins is a proposed mechanism, not directly established by the cited structural imaging.
- DOI:10.1128/mBio.00243-16 Kawamoto et al. 2016 measured structural periodicity in frozen-hydrated attachment organelles by electron cryotomography and proposed a gliding mechanism from the observed variation. The cryotomograms do not directly image internal-core deformation during live gliding.
- DOI:10.1371/journal.ppat.1005299 Nakane et al. 2015 integrated surface and internal-core protein maps into a model for gliding motility.
- DOI:10.1371/journal.ppat.1009621 Nakane et al. 2021 linked engineered HMW2 length to organelle length and gliding speed. Dual-color fluorescence tracking at 50 Hz in 20 cells did not detect large stepwise displacement. This limits the large-deformation model without excluding all smaller conformational changes.

Mechanism graphs

Internal-core proteins organize a polar adhesin-bearing attachment organelle (FUNCTION)

HMW2, P65, and HMW3 organize the terminal button and paired plates of the internal core. The polar extension positions P1/P40/P90 and P30 adhesins on the surface, coupling cytadherence with attachment-organelle-dependent gliding.

Subject	Predicate	Object	Evidence
HMW2 paired-plate scaffold	forms scaffold within	attachment-organelle internal core	`DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 mapped HMW2 along the paired plates in the internal core.
P65 terminal-button protein	localizes to	attachment-organelle internal core	`DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 placed P65 in the terminal-button substructure.
HMW3 terminal-button protein	localizes to	attachment-organelle internal core	`DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 placed HMW3 at the boundary with the paired plates.
attachment-organelle internal core	extends within	attachment organelle	`DOI:10.1128/mBio.00243-16` Kawamoto et al. 2016 resolved knoblike surface particles and an internal core in the polar protrusion by electron cryotomography.
P1 adhesin surface complex	clusters on	attachment organelle	`DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 summarize P1, P40, and P90 as surface proteins distributed around the core.
P30 tip adhesin	localizes to	attachment organelle	`DOI:10.1371/journal.ppat.1005299` Nakane et al. 2015 mapped P30 to the front surface of the organelle.
P30 tip adhesin	supports	host-cell cytadherence	`DOI:10.1128/JB.181.4.1079-1087.1999` Romero-Arroyo et al. 1999 showed that P30 mutants are defective for cytadherence.
attachment organelle	mediates	attachment-organelle-dependent gliding motility	`DOI:10.1128/mBio.00243-16` Kawamoto et al. 2016 analyzed attachment organelle periodicity in the gliding mechanism by electron cryotomography.

Evidence

DOI:10.1046/j.1365-2958.2003.03899.x Krause and Balish 2004, Cellular engineering in a minimal microbe: structure and assembly of the terminal organelle of Mycoplasma pneumoniae, Molecular Microbiology.
DOI:10.1371/journal.ppat.1005299 Nakane et al. 2015, Systematic Structural Analyses of Attachment Organelle in Mycoplasma pneumoniae, PLOS Pathogens.
DOI:10.1128/mBio.00243-16 Kawamoto et al. 2016, Periodicity in Attachment Organelle Revealed by Electron Cryotomography Suggests Conformational Changes in Gliding Mechanism of Mycoplasma pneumoniae, mBio.
DOI:10.1371/journal.ppat.1009621 Nakane et al. 2021, Molecular ruler of the attachment organelle in Mycoplasma pneumoniae, PLOS Pathogens.
DOI:10.1128/JB.181.4.1079-1087.1999 Romero-Arroyo et al. 1999, Mycoplasma pneumoniae Protein P30 Is Required for Cytadherence and Associated with Proper Cell Development, Journal of Bacteriology.
DOI:10.1186/s12866-025-04320-w Chen et al. 2025, Unraveling the role of distinct cytoskeletal motility structures in Mycoplasma pneumoniae relatives, BMC Microbiology.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=272634 NCBI full lineage checked 2026-10-10 places Mycoplasmoides pneumoniae M129 under Mycoplasmoidales and Mycoplasmatota (NCBITaxon:544448), not under the current Mollicutes class. This authority supplies identifier scope, not experimental structure-presence evidence.
https://rest.uniprot.org/taxonomy/544448.json UniProt taxonomy checked 2026-10-10 confirms active taxon 544448 as phylum Mycoplasmatota; the M129 lineage includes this phylum.
DOI:10.1111/mmi.13937 Krause et al. 2018, Electron cryotomography of Mycoplasma pneumoniae mutants correlates terminal organelle architectural features and function, Molecular Microbiology.

Curation history

2026-09-06T15:02:57Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-06T15:04:48Z claude · EXPANDED_RECORD — Added a terminal-organelle synonym, GO parent and membrane part, P1/P30/HMW2/terminal-button components, Mollicutes and Bacteria taxonomy, a Mycoplasmoides pneumoniae M129 example, cytadherence and gliding functions, record evidence, and a polar-core adhesion graph.
2026-09-06T15:24:25Z claude · REVIEW_ISSUE_207 — Resolved issue #207 by splitting a grouped P65/HMW3 terminal-button protein-complex row into separate P65 and HMW3 protein components and updating the graph component references.
2026-09-08T07:37:54Z uniprot_sl · SEED_PROTEIN_EXAMPLES — Added 3 taxon-paired protein example(s) from UniProtKB reviewed entries annotated to SL-0020 (Attachment organelle), matched to components by gene symbol, each carrying UniProt's ECO:0000269 PubMed evidence for the localisation.
2026-10-10T07:08:35Z claude · ADDRESS_REVIEW — Addressed #2118: corrected P1/P40/P90 assembly essentiality to DISPENSABLE using class IV-22 imaging; retained constituent status, functional limits and other component claims. Preserved PROPOSED status.
2026-10-10T07:54:18Z claude · ADDRESS_REVIEW — Addressed #2120: qualified internal-core deformation coupling as a proposed gliding mechanism, corrected frozen ECT imaging context, and attached the bounded 2021 live-tracking result. Retained gliding function, component claims and PROPOSED status.
2026-10-10T19:29:54Z claude · ADDRESS_REVIEW — Addressed #2124: grounded the bounded distribution to current Mycoplasmatota rather than historical Mollicutes usage; retained VARIABLE, M129 example and PROPOSED status. Addressed #2123: corrected P30 assembly essentiality to DISPENSABLE with II-3 mutant evidence; retained constituent, adhesion and morphology roles.

Source: data/structures/appendage/attachment_organelle.yaml