Definition
SecY protein is a core component of the SecYEG translocon complex, which mediates the translocation of nascent polypeptides across the cytoplasmic membrane in bacteria and archaea. It forms the channel through which unfolded proteins are exported or integrated into the membrane.
Overview
The SecYEG complex functions as the central channel of the general secretory (Sec) pathway, a highly conserved system responsible for transporting proteins destined for the periplasmic space, the outer membrane, or secretion outside the cell. SecY pairs with the membrane proteins SecE and SecG to create a heterotrimeric channel. The complex interacts with the ATP‑binding cassette (ABC) motor SecA, which drives the translocation process using ATP hydrolysis, as well as with signal recognition particle (SRP) components for co‑translational insertion of membrane proteins. SecY is essential for cell viability in most bacteria, as it facilitates the proper localization of a large portion of the proteome.
Etymology/Origin
The name “SecY” derives from the sec (secretion) operon originally identified in Escherichia coli. The letters “Y”, “E”, and “G” designate the individual gene products within the operon; “SecY” was the third gene identified, following secA and secB. The term reflects its functional role in the secretory pathway.
Characteristics
| Feature | Description |
|---|---|
| Gene | secY (also known as yajC in some species) |
| Protein family | SecY family; part of the larger SecY/ Sec61/ Oxa1 superfamily |
| Size | Approximately 300–350 amino acids (≈ 30–35 kDa) depending on the organism |
| Topology | Polytopic membrane protein with ten transmembrane α‑helices arranged in two pseudo‑symmetrical halves |
| Key domains | Central pore loop containing a conserved “plug” helix; a “pore ring” formed by conserved hydrophobic residues; cytoplasmic loops that interact with SecA and ribosomal components |
| Localization | Integral inner (cytoplasmic) membrane protein |
| Conservation | Highly conserved across bacteria and archaea; eukaryotic ortholog is Sec61α |
| Function | Forms the protein-conducting channel; provides the path for unfolded substrates; interacts with SecA (post‑translational pathway) and SRP (co‑translational pathway) |
| Regulation | Expression is typically coordinated with other Sec components; transcription is often part of the sec operon, regulated by the sigma factor σ^70 and stress‑responsive regulators |
| Structural data | High‑resolution crystal structures of the SecYEG complex have been solved (e.g., PDB IDs 1RHZ, 3J01), revealing the closed and open conformations of the channel |
Related Topics
- SecYEG translocon – the heterotrimeric channel comprising SecY, SecE, and SecG.
- SecA ATPase – peripheral motor protein that drives post‑translational protein translocation through SecYEG.
- Signal recognition particle (SRP) pathway – co‑translational targeting system that delivers nascent membrane proteins to SecYEG.
- Sec61α – eukaryotic homolog of SecY, forming the core of the Sec61 translocon in the endoplasmic reticulum.
- Protein secretion systems (Sec, Tat, Type I–VII) – various bacterial mechanisms for exporting proteins; SecY is central to the Sec (general secretory) system.
- Membrane protein insertion – process by which integral membrane proteins are integrated into the lipid bilayer via SecYEG or alternative pathways (e.g., YidC).
References – Primary literature and structural databases (e.g., UniProt entry P0A7B1 for E. coli SecY, Protein Data Bank).