|eubacterial secY protein|
Structure of a protein-conducting channel.
Secretion of some proteins carrying a signal-peptide across the inner membrane in Gram-negative bacteria occurs via the preprotein translocase pathway. Proteins are produced in the cytoplasm as precursors, and require a chaperone subunit to direct them to the translocase component within the membrane. From there, the mature proteins are either targeted to the outer membrane, or remain as periplasmic proteins. The translocase protein subunits are encoded on the bacterial chromosome.
The translocase pathway comprises 7 proteins, including a chaperone protein (SecB), an ATPase (SecA), an integral membrane complex (SecY, SecE and SecG), and two additional membrane proteins that promote the release of the mature peptide into the periplasm (SecD and SecF). The chaperone protein SecB is a highly acidic homotetrameric protein that exists as a "dimer of dimers" in the bacterial cytoplasm. SecB maintains preproteins in an unfolded state after translation, and targets these to the peripheral membrane protein ATPase SecA for secretion. The structure of the Escherichia coli SecYEG assembly revealed a sandwich of two membranes interacting through the extensive cytoplasmic domains. Each membrane is composed of dimers of SecYEG. The monomeric complex contains 15 transmembrane helices.
The eubacterial SecY protein interacts with the signal sequences of secretory proteins as well as with two other components of the protein translocation system: SecA and SecE. SecY is an integral plasma membrane protein of 419 to 492 amino acid residues that apparently contains 10 transmembrane (TM), 6 cytoplasmic and 5 periplasmic regions.
Cytoplasmic regions 2 and 3, and TM domains 1, 2, 4, 5, 7 and 10 are well conserved: the conserved cytoplasmic regions are believed to interact with cytoplasmic secretion factors, while the TM domains may participate in protein export. Homologs of SecY are found in archaebacteria. SecY is also encoded in the chloroplast genome of some algae where it could be involved in a prokaryotic-like protein export system across the two membranes of the chloroplast endoplasmic reticulum (CER) which is present in chromophyte and cryptophyte algae.
Human proteins containing this domain
- Van den Berg B, Clemons WM, Collinson I, Modis Y, Hartmann E, Harrison SC, Rapoport TA (January 2004). "X-ray structure of a protein-conducting channel". Nature. 427 (6969): 36–44. doi:10.1038/nature02218. PMID 14661030.
- Bieker KL, Phillips GJ, Silhavy TJ (June 1990). "The sec and prl genes of Escherichia coli". Journal of Bioenergetics and Biomembranes. 22 (3): 291–310. doi:10.1007/BF00763169. PMID 2202721.
- Driessen AJ (May 2001). "SecB, a molecular chaperone with two faces". Trends in Microbiology. 9 (5): 193–6. doi:10.1016/S0966-842X(01)01980-1. PMID 11336818.
- Müller JP (July 1999). "Effects of pre-protein overexpression on SecB synthesis in Escherichia coli". FEMS Microbiology Letters. 176 (1): 219–27. doi:10.1016/s0378-1097(99)00239-6. PMID 10418149.
- Breyton C, Haase W, Rapoport TA, Kühlbrandt W, Collinson I (August 2002). "Three-dimensional structure of the bacterial protein-translocation complex SecYEG". Nature. 418 (6898): 662–5. doi:10.1038/nature00827. PMID 12167867.
- Ito K (September 1992). "SecY and integral membrane components of the Escherichia coli protein translocation system". Molecular Microbiology. 6 (17): 2423–8. doi:10.1111/j.1365-2958.1992.tb01417.x. PMID 1406280.
- Suh JW, Boylan SA, Thomas SM, Dolan KM, Oliver DB, Price CW (February 1990). "Isolation of a secY homologue from Bacillus subtilis: evidence for a common protein export pathway in eubacteria". Molecular Microbiology. 4 (2): 305–14. doi:10.1111/j.1365-2958.1990.tb00597.x. PMID 2110998.
- Auer J, Spicker G, Böck A (June 1991). "Presence of a gene in the archaebacterium Methanococcus vannielii homologous to secY of eubacteria". Biochimie. 73 (6): 683–8. doi:10.1016/0300-9084(91)90048-6. PMID 1764515.
- Douglas SE (February 1992). "A secY homologue is found in the plastid genome of Cryptomonas phi". FEBS Letters. 298 (1): 93–6. doi:10.1016/0014-5793(92)80029-G. PMID 1544427.