SecYEG translocon complex

cellstructuremech:secyeg_translocon_complex · Secretion system · Multiprotein complex · Proposed

A bacterial cytoplasmic-membrane Sec-pathway protein-conducting channel built from SecY, SecE, and SecG, through which unfolded secretory proteins or nascent membrane proteins move during translocation or membrane insertion. [DOI:10.1038/nrmicro.2016.161]

Synonyms: SecYEG translocon; SecYEG channel; bacterial SecYEG complex

Part of: GO:0031522 — cell envelope Sec protein transport complex (no local record)

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
SecY protein-conducting channel subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	secY, prlA	ESSENTIAL	Multi-pass membrane subunit that forms the hourglass-shaped protein-conducting pore and lateral gate of the SecYEG channel. `DOI:10.1146/annurev-biophys-050511-102312` Park and Rapoport 2012 review SecY/Sec61 as the central pore-forming subunit of the conserved protein-conducting channel. `DOI:10.1038/s41467-019-10918-2` Ma et al. 2019 resolved a bacterial substrate-engaged SecA-SecY translocation machine that shows preprotein inside SecY.
SecE clamp subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	secE, prlG	ESSENTIAL	Membrane clamp that braces the two halves of SecY and stabilizes the protein-conducting channel. `DOI:10.1146/annurev-biophys-050511-102312` Park and Rapoport 2012 review SecE as the subunit that embraces SecY/Sec61 and holds the channel together. `DOI:10.1093/emboj/16.10.2756` Duong and Wickner 1997 dissected the catalytic roles of the SecYE, SecG, and SecDF-YajC subunits of the E. coli preprotein translocase holoenzyme.
SecG accessory channel subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	secG	ESSENTIAL	Small membrane subunit that associates with SecY and SecE to form the bacterial SecYEG heterotrimer. `DOI:10.1038/nrmicro.2016.161` Tsirigotaki et al. 2017 review SecG as a bacterial SecYEG channel subunit. `DOI:10.1093/emboj/16.10.2756` Duong and Wickner 1997 separated the functions of SecYE, SecG, and SecDF-YajC in purified E. coli preprotein translocase.

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.

SecY protein-conducting channel subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0AGA2`	Protein translocase subunit SecY	secY	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene prlA, which UniProt lists under the primary name secY, in Escherichia coli K-12, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `https://www.uniprot.org/uniprotkb/P0AGA2` UniProtKB reviewed (Swiss-Prot) entry P0AGA2, the single reviewed entry for gene prlA in Escherichia coli K-12. Establishes the accession and gene identity only; the component's membership in this structure rests on the record's own sources.

SecE clamp subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0AG96`	Protein translocase subunit SecE	secE	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) The single reviewed UniProtKB entry for gene prlG, which UniProt lists under the primary name secE, in Escherichia coli K-12, a taxon this record names. Identifier for the component's declared gene symbol; it is not itself evidence that the protein is part of this structure. `PMID:15919996` Daley DO et al. 2005, ‘Global topology analysis of the Escherichia coli inner membrane proteome.’, Science. ECO:0000269 experimental evidence cited by UniProt for the 'Cell inner membrane' localisation of P0AG96.

Taxonomic distribution

NCBITaxon:2 Bacteria — COMMON: The SecYEG channel is broadly conserved in bacterial cytoplasmic membranes as the core of the Sec protein-export route. [DOI:10.1038/nrmicro.2016.161]

Canonical examples

NCBITaxon:562 Escherichia coli — Genetic and biochemical model for the SecYEG/SecA translocase and the SecYEG-SecDF-YajC holoenzyme. [DOI:10.1093/emboj/16.10.2756]

Functions

protein transport by the Sec complex GO:0043952 — The SecYEG channel translocates unfolded secretory preproteins across the bacterial cytoplasmic membrane via the Sec complex.
- GO:0043952 GO:0043952 defines unfolded-protein transport across Gram-positive and Gram-negative bacterial cytoplasmic membranes by the Sec complex.
- DOI:10.1038/nrmicro.2016.161 Tsirigotaki et al. 2017 review the Sec pathway as the main bacterial export route for unfolded secretory preproteins and membrane proteins.

Mechanism graphs

SecA drives preproteins through SecYEG (FUNCTION)

SecY and SecE form the stabilized channel core, SecG completes the bacterial SecYEG heterotrimer, and the SecA ATPase drives unfolded preproteins through the SecY pore during post-translational secretion.

Subject	Predicate	Object	Evidence
SecE clamp subunit	stabilizes	SecY protein-conducting channel subunit	`DOI:10.1146/annurev-biophys-050511-102312` Park and Rapoport 2012 review SecE's bracing role in the SecY/Sec61 channel.
SecY protein-conducting channel subunit	forms pore of	SecYEG translocon complex	`DOI:10.1038/nature17163` Li et al. 2016 captured a substrate-engaged SecY channel with preprotein density in the pore.
SecG accessory channel subunit	associates with	SecY protein-conducting channel subunit	`DOI:10.1093/emboj/16.10.2756` Duong and Wickner 1997 characterized SecG separately from SecYE within the E. coli preprotein translocase.
SecA ATPase	binds	SecYEG translocon complex	`DOI:10.1038/s41467-019-10918-2` Ma et al. 2019 resolved a substrate-engaged bacterial SecA-SecY translocation machine.
SecA ATPase	pushes	unfolded Sec preprotein	`DOI:10.1038/nrmicro.2016.161` Tsirigotaki et al. 2017 review ATP-driven SecA motor action during Sec-dependent protein export.
SecYEG translocon complex	carries out	protein transport by the Sec complex	`GO:0043952` GO:0043952 defines bacterial protein transport by the Sec complex across the cytoplasmic membrane.

Discussions

CURATION_TODO (OPEN): Should SecDF-YajC and YidC be modeled as SecYEG components, as a SecYEG-SecDF-YajC-YidC holo-translocon subrecord, or only as associated machinery? GO:0031522 includes SecA, SecD, SecF, and YajC in the broader cell envelope Sec protein transport complex, and bacterial holo-translocon papers add SecDF-YajC and YidC to SecYEG. This first record captures only the named heterotrimeric channel core.

Evidence

DOI:10.1038/nrmicro.2016.161 Tsirigotaki et al. 2017, Protein export through the bacterial Sec pathway, Nature Reviews Microbiology.
DOI:10.1146/annurev-biophys-050511-102312 Park and Rapoport 2012, Mechanisms of Sec61/SecY-Mediated Protein Translocation Across Membranes, Annual Review of Biophysics.
DOI:10.1093/emboj/16.10.2756 Duong and Wickner 1997, Distinct catalytic roles of the SecYE, SecG and SecDFyajC subunits of preprotein translocase holoenzyme, The EMBO Journal.
DOI:10.1038/nature17163 Li et al. 2016, Crystal structure of a substrate-engaged SecY protein-translocation channel, Nature.
DOI:10.1038/s41467-019-10918-2 Ma et al. 2019, Structure of the substrate-engaged SecA-SecY protein translocation machine, Nature Communications.

Curation history

2026-09-07T00:06:51Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-07T00:07:36Z claude · EXPANDED_RECORD — Added SecYEG synonymy, protein-complex parentage, broader GO:0031522 Sec-complex parthood, SecY, SecE, and SecG components, bacterial taxonomic scope, an Escherichia coli canonical example, GO:0043952 protein transport function grounding, record evidence, a SecA-driven preprotein-translocation graph, and a Sec holo-translocon boundary TODO.
2026-09-07T00:08:20Z claude · REVIEW_FIX — Resolved issue #218 by narrowing the GO:0043952 function description to unfolded secretory preprotein transport across the bacterial cytoplasmic membrane, leaving SecYEG lateral-gate membrane insertion outside the GO-grounded function.
2026-09-08T07:40:13Z uniprot_genes · SEED_PROTEIN_EXAMPLES — #183: added 2 protein example(s) by resolving each of the component's declared gene symbols to the single reviewed UniProtKB entry for that symbol in a taxon this record names, deduplicated by accession. Symbols resolving to more than one reviewed entry were skipped rather than chosen between.

Source: data/structures/secretion_system/secyeg_translocon_complex.yaml