curli

GO:0098774 · Appendage · Appendage · Proposed

Extracellular amyloid fibers assembled from CsgA by the Csg secretion and nucleation machinery that form a pilus subtype in enteric biofilm matrices. [GO:0098774]

Synonyms: curli fimbriae; bacterial amyloid fibers

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
CsgA major curlin subunit	Protein	part of		csgA		ESSENTIAL	Secreted amyloid-forming subunit that polymerizes into the curli fiber. `DOI:10.1128/ecosalplus.ESP-0037-2018` Bhoite et al. 2019 review CsgA as the major curli subunit secreted through the type VIII curli pathway. `DOI:10.1126/science.1067484` Chapman et al. 2002 showed that the Escherichia coli csg operons direct amyloid fiber formation.
CsgB nucleator subunit	Protein	part of		csgB		ESSENTIAL	Cell-surface nucleator that templates CsgA polymerization into curli. `DOI:10.1128/ecosalplus.ESP-0037-2018` Bhoite et al. 2019 review CsgB-dependent nucleation during curli assembly.

Taxonomic distribution

NCBITaxon:2 Bacteria — VARIABLE: Curli-family functional amyloid systems are widespread but unevenly distributed among bacterial genomes. [DOI:10.1371/journal.pone.0051274]

Canonical examples

NCBITaxon:562 Escherichia coli — The K-12 curli operons provided a genetic model for CsgA and CsgB amyloid-fiber assembly. [DOI:10.1126/science.1067484]

Functions

curli assembly GO:0098775 — CsgA subunits are secreted and nucleated on the cell surface to build an extracellular amyloid fiber.
- DOI:10.1128/ecosalplus.ESP-0037-2018 The EcoSal Plus review frames curli biogenesis as bacterial amyloid assembly by the type VIII secretion pathway.
biofilm matrix adhesion — Curli fibers contribute an adhesive amyloid scaffold to enterobacterial extracellular matrices.
- DOI:10.1146/annurev.micro.60.080805.142106 Barnhart and Chapman 2006 review curli functions in surface adhesion, cell aggregation, and biofilm formation.

Mechanism graphs

Csg secretion and nucleation build the curli fiber (ASSEMBLY)

The outer-membrane CsgG pore and accessory factors move CsgA to the cell surface, CsgB nucleates CsgA polymerization, and the resulting amyloid polymer forms the curli fiber.

Subject	Predicate	Object	Evidence
CsgG outer-membrane secretion pore	exports	CsgA major curlin subunit	`DOI:10.1111/j.1365-2958.2005.04997.x` Robinson et al. 2006 established the outer-membrane CsgG protein as the secretion route for curli fiber subunits.
CsgF cell-surface adaptor	positions	CsgB nucleator subunit	`DOI:10.1073/pnas.0812143106` Nenninger et al. 2009 showed that CsgF is needed for localized, efficient curli nucleation by the CsgB pathway.
CsgA major curlin subunit	reaches	surface-localized CsgA	`DOI:10.1038/s41467-019-14145-7` Yan et al. 2020 analyzed substrate-bound CsgF-CsgG secretion channel complexes.
CsgB nucleator subunit	nucleates polymerization of	surface-localized CsgA	`DOI:10.1128/ecosalplus.ESP-0037-2018` Bhoite et al. 2019 review CsgB nucleation of CsgA amyloid assembly.
surface-localized CsgA	polymerizes into	curli	`DOI:10.1126/science.1067484` Chapman et al. 2002 connected the csg operons to extracellular amyloid fiber formation in Escherichia coli.
curli	is assembled by	curli assembly	`DOI:10.1128/ecosalplus.ESP-0037-2018` Bhoite et al. 2019 review the type VIII secretion pathway as the route for curli fiber biogenesis.

Discussions

CURATION_TODO (RESOLVED): Decide whether GO:0062155 curli secretion complex needs its own CellStructureMech record. GO has an exact curli secretion complex term for the Csg secretion machinery. This curli record models that secretion route only in the assembly graph because it exports fiber subunits but is not itself part of the amyloid pilus.

Evidence

DOI:10.1146/annurev.micro.60.080805.142106 Barnhart MM and Chapman MR 2006, Curli biogenesis and function, Annual Review of Microbiology.
DOI:10.1128/ecosalplus.ESP-0037-2018 Bhoite S, Van Gerven N, Chapman MR and Remaut H 2019, Curli Biogenesis: Bacterial Amyloid Assembly by the Type VIII Secretion Pathway, EcoSal Plus.
DOI:10.1038/s41467-019-14145-7 Yan et al. 2020 reconstituted and structurally analyzed curli substrate recognition by CsgF-CsgG secretion channel complexes.

Curation history

2026-09-06T07:14:04Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-06T07:16:44Z claude · EXPANDED_RECORD — Added synonyms, parentage, components, taxonomy, a canonical example, function, evidence, and a source-bounded mechanism graph.
2026-09-06T07:48:00Z claude · FIX_DISCUSSION_ANCHOR — Repointed the curli secretion complex boundary TODO to the curli assembly graph so its attaches_to anchor resolves.
2026-09-29T05:29:10Z codex · EXPANDED_RECORD — Resolved the curli secretion-complex boundary TODO after adding GO:0062155 as a standalone secretion-system record.
2026-09-29T05:44:44Z codex · EXPANDED_RECORD — Softened the resolved curli secretion-complex rationale after PR review to avoid treating GO:0062155 as an exact CsgE/F/G component-boundary decision.

Source: data/structures/appendage/curli.yaml