archaeal cannula

cellstructuremech:archaeal_cannula · Appendage · Appendage · Proposed

An extracellular hollow tubular archaeal cell projection, characterized in Pyrodictium species, that extends from the cell envelope as a proteinaceous filament and forms networks between cells. [DOI:10.1016/S1047-8477(02)00581-6]

Synonyms: cannulae

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
CanA cannula glycoprotein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Cannula glycoprotein whose recombinant mature form assembles into hollow cannula-like fibers in vitro through calcium coordination and donor-strand complementation; warming accelerates assembly under the tested conditions. `DOI:10.1038/s41467-025-64120-8` Sleutel et al. 2025 resolved in vitro filaments assembled from recombinant P. abyssi TAG11 CanA. The native ex vivo AV2 cannula reconstruction in the same paper instead identifies the distinct homologue CanX as its major subunit. `DOI:10.1038/s41598-025-13242-6` Munte et al. 2025 solved the NMR solution structure of the N-terminally truncated K1-CanA construct and separately characterized divalent-ion-induced polymerization of full-length recombinant CanA.
CanX cannula glycoprotein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Major glycoprotein subunit of native cannulae resolved from P. abyssi AV2, joined by donor-strand complementation and calcium-coordinated interfaces. This does not establish obligatory coassembly with CanA or exclude low-occupancy minor subunits. `DOI:10.1038/s41467-025-64120-8` Sleutel et al. 2025 assigned the native AV2 cannula cryo-EM map to CanX, a homologue distinct from the recombinant TAG11 CanA used in their in vitro assembly experiments.

Taxonomic distribution

NCBITaxon:54256 Pyrodictium abyssi — COMMON: Pyrodictium abyssi produces extracellular cannulae that were visualized as a cell-associated tubular network in ultrastructural studies. [DOI:10.1006/jsbi.1995.1032]

Canonical examples

NCBITaxon:54256 Pyrodictium abyssi — Hyperthermophilic archaeon in which cannulae were shown by cryo-electron tomography to enter the periplasmic space without crossing into the cytoplasm. [DOI:10.1016/S1047-8477(02)00581-6]

Functions

extracellular Pyrodictium cell-network formation — Cannulae extend from the Pyrodictium cell envelope and physically interconnect cells in an extracellular network; the transported cargo or signaling role of the network remains unresolved.
- DOI:10.1016/S1047-8477(02)00581-6 Nickell et al. 2003 used cryo-electron tomography to show how Pyrodictium cannulae contact the cell envelope and interconnect cells.
- DOI:10.1006/jsbi.1995.1032 Rieger et al. 1995 characterized the extracellular network of Pyrodictium abyssi cannulae in ultrastructural sections.

Mechanism graphs

Recombinant CanA coordinates calcium during in vitro fiber assembly (ASSEMBLY)

Recombinant mature P. abyssi TAG11 CanA coordinates calcium and undergoes donor-strand complementation to assemble hollow cannula-like fibers in vitro.

Subject	Predicate	Object	Evidence
CanA cannula glycoprotein	coordinates	calcium ion	`DOI:10.1038/s41467-025-64120-8` Sleutel et al. 2025 resolved calcium-bound interfaces in recombinant TAG11 CanA filaments assembled in vitro.
CanA cannula glycoprotein	polymerizes into	in vitro CanA cannula-like fiber	`DOI:10.1038/s41467-025-64120-8` Sleutel et al. 2025 used cryo-EM to resolve recombinant CanA filaments; their separate native AV2 reconstruction was composed principally of CanX. `DOI:10.1038/s41598-025-13242-6` Munte et al. 2025 assayed divalent-ion-induced polymerization of full-length recombinant CanA, distinct from the truncated K1-CanA NMR construct.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral protein-family groundings for CanA and CanX and the component boundaries of CanB and CanC. The first archaeal cannula record keeps only CanA as a reviewed label-only component because this pass did not verify an exact Pfam, InterPro or NCBIfam family for CanA or resolve whether the homologous CanB and CanC glycoproteins should be separate curated components. Follow-up inspection of Sleutel et al. 2025 distinguishes the native AV2 major subunit CanX from recombinant TAG11 CanA. Both are now represented separately without implying that they coexist in one native filament; exact family mappings and CanB/CanC component boundaries remain unresolved.
CURATION_TODO (OPEN): Resolve the physiological cargo or signaling role of the Pyrodictium cannula network. Electron microscopy supports cannula-mediated physical interconnection of Pyrodictium cells, but the exchanged material, if any, remains unresolved.

Evidence

DOI:10.1006/jsbi.1995.1032 Rieger et al. 1995, Ultrastructure of the hyperthermophilic archaeon Pyrodictium abyssi, Journal of Structural Biology.
DOI:10.1016/S1047-8477(02)00581-6 Nickell et al. 2003, Pyrodictium cannulae enter the periplasmic space but do not enter the cytoplasm, as revealed by cryo-electron tomography, Journal of Structural Biology.
DOI:10.1038/s41467-025-64120-8 Sleutel et al. 2025, Donor strand complementation and calcium ion coordination drive the chaperone-free polymerization of archaeal cannulae, Nature Communications.
DOI:10.1038/s41598-025-13242-6 Munte et al. 2025, Biophysical characterization and solution structure of the cannulae-forming protein CanA from the hyperthermophilic archaeon Pyrodictium abyssi, Scientific Reports.

Curation history

2026-09-11T14:41:04Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-11T14:41:51Z codex · EXPANDED_RECORD — Added archaeal cannula synonymy, GO cell-projection parentage, a label-only CanA glycoprotein component, Pyrodictium abyssi scope and exemplar rows, cell-network formation function, DOI evidence, a calcium-dependent CanA assembly graph, and TODOs for CanA-family grounding and cannula network function.
2026-09-11T14:46:58Z codex · ADDRESS_REVIEW — Resolved #501 by scoping the taxonomic and canonical-example notes to their single direct citations, and resolved #502 by making CanA the subject of the calcium-coordination assembly edge.
2026-10-10T05:19:03Z claude · ADDRESS_REVIEW — Separated native AV2 CanX from recombinant TAG11 CanA evidence, added a label-only CanX constituent, restricted the CanA assembly graph to the demonstrated in vitro system, and named K1-CanA as the solved NMR construct. Preserved PROPOSED status and unresolved family, minor-subunit and physiological-function questions.

Source: data/structures/appendage/archaeal_cannula.yaml