SecY protein

{{Pfam_box

| Symbol = SecY

| Name = SecY protein/Sec61α

| image = PDB 1rh5 EBI.jpg

| width =

| caption = Structure of a protein-conducting channel.{{cite journal | vauthors = Van den Berg B, Clemons WM, Collinson I, Modis Y, Hartmann E, Harrison SC, Rapoport TA | title = X-ray structure of a protein-conducting channel | journal = Nature | volume = 427 | issue = 6969 | pages = 36–44 | date = January 2004 | pmid = 14661030 | doi = 10.1038/nature02218 | bibcode = 2004Natur.427...36B | s2cid = 4360143 }}

| Pfam= PF00344

| InterPro= IPR002208

| SMART=

| PROSITE = PDOC00612

| SCOP = 1rh5

| TCDB = 3.A.5

| OPM family= 19

| OPM protein= 1rh5

| PDB=

| Membranome superfamily = 165

}}

The SecY protein is the main transmembrane subunit of the bacterial Sec export pathway and of a protein-secreting ATPase complex, also known as a SecYEG translocon. Homologs of the SecYEG complex are found in eukaryotes and in archaea, where the subunit is known as Sec61α.{{cite journal | vauthors = Auer J, Spicker G, Böck A | title = Presence of a gene in the archaebacterium Methanococcus vannielii homologous to secY of eubacteria | journal = Biochimie | volume = 73 | issue = 6 | pages = 683–8 | date = June 1991 | pmid = 1764515 | doi = 10.1016/0300-9084(91)90048-6 }}

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.{{cite journal | vauthors = Bieker KL, Phillips GJ, Silhavy TJ | title = The sec and prl genes of Escherichia coli | journal = Journal of Bioenergetics and Biomembranes | volume = 22 | issue = 3 | pages = 291–310 | date = June 1990 | pmid = 2202721 | doi = 10.1007/BF00763169 | s2cid = 10694864 }} 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{{cite journal | vauthors = Driessen AJ | title = SecB, a molecular chaperone with two faces | journal = Trends in Microbiology | volume = 9 | issue = 5 | pages = 193–6 | date = May 2001 | pmid = 11336818 | doi = 10.1016/S0966-842X(01)01980-1 | url = https://pure.rug.nl/ws/files/3619679/2001TrendsMicrobiolDriessen.pdf | hdl = 11370/4e5ebfac-d58c-42db-b42e-01c22d469a82 | hdl-access = free }} 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.{{cite journal | vauthors = Müller JP | title = Effects of pre-protein overexpression on SecB synthesis in Escherichia coli | journal = FEMS Microbiology Letters | volume = 176 | issue = 1 | pages = 219–27 | date = July 1999 | pmid = 10418149 | doi = 10.1111/j.1574-6968.1999.tb13665.x }}

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.{{cite journal | vauthors = Suh JW, Boylan SA, Thomas SM, Dolan KM, Oliver DB, Price CW | title = Isolation of a secY homologue from Bacillus subtilis: evidence for a common protein export pathway in eubacteria | journal = Molecular Microbiology | volume = 4 | issue = 2 | pages = 305–14 | date = February 1990 | pmid = 2110998 | doi = 10.1111/j.1365-2958.1990.tb00597.x | s2cid = 27373166 }} 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.{{cite journal | vauthors = Douglas SE | title = A secY homologue is found in the plastid genome of Cryptomonas phi | journal = FEBS Letters | volume = 298 | issue = 1 | pages = 93–6 | date = February 1992 | pmid = 1544427 | doi = 10.1016/0014-5793(92)80029-G | s2cid = 22351990 | doi-access = free | bibcode = 1992FEBSL.298...93D }}