cytoophidium

GO:0097268 · Cytoskeleton · Filament · Proposed

A filamentous, membrane-less subcellular structure composed primarily of polymerized metabolic enzymes, most notably cytidine triphosphate synthase (CTPS). Cytoophidia are evolutionarily conserved structures found across archaea, bacteria, and eukaryotes. [GO:0097268]

Synonyms: CtpS filament; CTPS cytoophidium

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
CTP synthase	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	pyrG, ctpS		UNKNOWN	Filament-forming cytidine triphosphate synthase enzyme that assembles into CTPS cytoophidia in lineages where this constituent has been characterized. `DOI:10.1038/ncb2087` Ingerson-Mahar et al. 2010 showed that Caulobacter CtpS colocalizes with inner-curvature filaments, that filament abundance responds to untagged CtpS levels and to the CtpS inhibitor DON, and that Escherichia coli CtpS also forms filaments in vivo and in vitro.

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.

CTP synthase

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q9A7K3`	CTP synthase	pyrG	Caulobacter vibrioides CB15 (`NCBITaxon:190650`)	REVIEWED
Role and evidence (1 reference) Reviewed Caulobacter CB15 CTP synthase encoded by pyrG/CC_1720, the CtpS homolog identified as the inner-curvature filament constituent in the discovery paper. `DOI:10.1038/ncb2087` Ingerson-Mahar et al. 2010 identified the Caulobacter CtpS homolog CC1720 as the protein whose fluorescent localization matched the electron-cryo-tomography inner-curvature filaments.
`UniProtKB:B8GW64`	CTP synthase	pyrG	Caulobacter vibrioides NA1000 (`NCBITaxon:565050`)	REVIEWED
Role and evidence (1 reference) Reviewed CTP synthase entry for Caulobacter vibrioides NA1000/CB15N, the strain background used for wild-type filament imaging. `DOI:10.1038/ncb2087` Ingerson-Mahar et al. 2010 imaged the Caulobacter CtpS-dependent inner-curvature filament in CB15N cells, now classified as Caulobacter vibrioides NA1000.

Taxonomic distribution

NCBITaxon:2 Bacteria — VARIABLE: CTPS cytoophidium occurrence is variable across Bacteria; Ingerson-Mahar et al. 2010 directly demonstrated CtpS filaments in Caulobacter and Escherichia coli. [DOI:10.1042/BST20221410]
NCBITaxon:2157 Archaea — VARIABLE: Guo and Liu 2023 reviewed CTPS cytoophidia as structures found across all three domains of life, including Archaea, without asserting universal archaeal presence. [DOI:10.1042/BST20221410]
NCBITaxon:2759 Eukaryota — VARIABLE: Guo and Liu 2023 reviewed CTPS cytoophidia as structures found across all three domains of life; this row records eukaryotic occurrence without asserting universal eukaryotic presence. [DOI:10.1042/BST20221410]
NCBITaxon:155892 Caulobacter vibrioides — COMMON: CtpS filaments were directly characterized in Caulobacter crescentus, now classified as Caulobacter vibrioides. [DOI:10.1038/ncb2087]

Canonical examples

NCBITaxon:565050 Caulobacter vibrioides NA1000 — CB15N/NA1000 laboratory strain in which wild-type inner-curvature filaments were imaged by electron cryo-tomography and connected to CtpS abundance. [DOI:10.1038/ncb2087]

Functions

Caulobacter cell-curvature regulation — Caulobacter CtpS filaments localize along the inner cell curvature and regulate curved morphology independently of CtpS catalytic activity.
- DOI:10.1038/ncb2087 Ingerson-Mahar et al. 2010 showed that CtpS filaments regulate Caulobacter cell curvature through a functional interaction with crescentin, separately from the enzyme's CTP biosynthetic activity.

Mechanism graphs

CtpS cytoophidia regulate Caulobacter curvature (FUNCTION)

Caulobacter CtpS polymerizes into an inner-curvature filament that functionally interacts with crescentin and supports curved cell morphology.

Subject	Predicate	Object	Evidence
CTP synthase	polymerizes into	cytoophidium	`DOI:10.1038/ncb2087` Ingerson-Mahar et al. 2010 used fluorescence microscopy and electron cryo-tomography to identify CtpS as the Caulobacter inner-curvature filament protein.
cytoophidium	localizes to	Caulobacter inner cell curvature	`DOI:10.1038/ncb2087` Ingerson-Mahar et al. 2010 followed mCherry-CtpS structures that elongated and moved to the inner cell curvature.
cytoophidium	functionally interacts with	crescentin filament	`DOI:10.1038/ncb2087` Ingerson-Mahar et al. 2010 connected the CtpS morphogenic role to a functional interaction with crescentin.
cytoophidium	regulates	curved Caulobacter morphology	`DOI:10.1038/ncb2087` Ingerson-Mahar et al. 2010 showed that Caulobacter CtpS overexpression and depletion perturb cell curvature and that the morphogenic effect is separable from catalytic activity.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral grounding for full-length cytoophidium-forming CTP synthase proteins. This first cytoophidium record curates the experimentally studied Caulobacter CtpS constituent without asserting that a catalytic CTPS domain, an ATP-grasp fold term or a generic enzyme family accession exactly denotes the filament-forming CTPS component class.
INTERPRETATION (RESOLVED): Crescentin is a functional interactor, not a curated cytoophidium constituent. The Caulobacter CtpS filament genetically and functionally interacts with the crescentin filament to regulate cell shape, but the discovery paper identifies CtpS as the protein constituent of the inner-curvature cytoophidium rather than crescentin as a cytoophidium subunit.

Evidence

GO:0097268 Gene Ontology defines cytoophidium as a filamentous membrane-less cellular component composed primarily of polymerized metabolic enzymes including CTPS.
DOI:10.1038/ncb2087 Ingerson-Mahar, Briegel, Werner, Jensen and Gitai 2010, 'The metabolic enzyme CTP synthase forms cytoskeletal filaments', Nature Cell Biology.
DOI:10.1042/BST20221410 Guo and Liu 2023 reviewed cytoophidia and CTPS-containing enzyme filaments across domains of life.

Curation history

2026-09-11T16:08:25Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-11T16:09:28Z codex · EXPANDED_RECORD — Added supramolecular-fiber parentage, CtpS and CTPS synonymy, label-only CTP synthase component curation, Caulobacter vibrioides scope, a cell-curvature function, DOI evidence, a nonmechanistic CtpS-to-crescentin graph, and CTP synthase grounding and crescentin boundary discussions.
2026-09-11T16:16:14Z codex · REVIEW_FIX — Addressed PR #515 review issues #516 and #517 by adding variable Bacteria, Archaea and Eukaryota cytoophidium distribution rows and narrowing broad CTP synthase essentiality to UNKNOWN.

Source: data/structures/cytoskeleton/cytoophidium.yaml