ER Translocon complex.[2] Many protein complexes are involved in protein synthesis. The actual production takes place in the ribosomes (grey and light blue). Through the ER translocon (green: Sec61, blue: TRAP complex, and red: oligosaccharyl transferase complex) the newly synthesized protein is transported across the membrane (gray) into the interior of the ER. Sec61 is the protein-conducting channel and the OST adds sugar moieties to the nascent protein.
OST is a component of the translocon in the endoplasmic reticulum (ER) membrane. A lipid-linked core-oligosaccharide is assembled at the membrane of the endoplasmic reticulum and transferred to selected asparagine residues of nascent polypeptide chains by the oligosaccharyl transferase complex.[3] The active site of OST is located about 4 nm from the lumenal face of the ER membrane.[4]
It usually acts during translation as the nascent protein is entering the ER, but this cotranslational glycosylation is nevertheless called a posttranslational modification. A few examples have been found of OST activity after translation is complete.[5][6] Current opinion is that post-translational activity may occur if the protein is poorly folded or folds slowly.[6]
Structure and functionedit
Yeast OST is composed of eight different membrane-spanning proteins in three subcomplexes (one of them is OST4).[7][8] These octomers do not form higher order oligomers, and three of the eight proteins are glycosylated themselves.[7] OST in mammals is known to have a similar composition.[9][10]
OST is thought to require many subunits because it must:[11]
Position itself near the translocon pore.
Recognize and bind oligosaccharyldolichol.
Scan the nascent protein in order to recognize and bind sequons.
Move these two large substrates into their proper locations and conformations.
Activate the Asnamidenitrogen atom for the actual transfer of oligosaccharide.
Release its substrates.
The catalytically active subunit of the OST is called STT3. Two paralogs exist in eukaryotes, termed STT3A and STT3B. STT3A is primarily responsible for cotranslational glycosylation of the nascent polypeptide as it enters the lumen of the endoplasmic reticulum whereas STT3B can also mediate posttranslational glycosylation.[12] The structure of PglB, the prokaryotic homolog of STT3 has been solved.[13] The high sequence similarity between the prokaryotic and the eukaryotic STT3 suggests that their structures are similar.
Clinical significanceedit
CDG syndromes are genetic disorders of the glycosylation pathway. They are labelled "Type I" if the defective gene is for an enzyme involved in the assembly or transfer of the Glc3Man9GlcNAc2-dolichol precursor. They are labelled "Type II" if the defective step occurs after the action of OST in the N-linked glycosylation pathway or involves O-linked glycosylation.[14]
^Wild R, Kowal J, Eyring J, Ngwa EM, Aebi M, Locher KP (2018). "Structure of the yeast oligosaccharyltransferase complex gives insight into eukaryotic N-glycosylation". Science. 359 (6375): 545–550. Bibcode:2018Sci...359..545W. doi:10.1126/science.aar5140. hdl:20.500.11850/228327. PMID 29301962.
^Pfeffer S, Dudek J, Gogala M, Schorr S, Linxweiler J, Lang S, Becker T, Beckmann R, Zimmermann R, Förster F (2014). "Structure of the mammalian oligosaccharyl-transferase complex in the native ER protein translocon". Nat. Commun. 5 (5): 3072. Bibcode:2014NatCo...5.3072P. doi:10.1038/ncomms4072. PMID 24407213.
^Zufferey R, Knauer R, Burda P, Stagljar I, te Heesen S, Lehle L, Aebi M (October 1995). "STT3, a highly conserved protein required for yeast oligosaccharyl transferase activity in vivo". EMBO J. 14 (20): 4949–60. doi:10.1002/j.1460-2075.1995.tb00178.x. PMC394598. PMID 7588624.
^Nilsson IM, von Heijne G (March 1993). "Determination of the distance between the oligosaccharyltransferase active site and the endoplasmic reticulum membrane". J. Biol. Chem. 268 (8): 5798–801. doi:10.1016/S0021-9258(18)53389-5. PMID 8449946.
^Pless DD, Lennarz WJ; Lennarz (January 1977). "Enzymatic conversion of proteins to glycoproteins". Proc. Natl. Acad. Sci. U.S.A. 74 (1): 134–8. Bibcode:1977PNAS...74..134P. doi:10.1073/pnas.74.1.134. PMC393212. PMID 264667.
^ abDuvet S, Op De Beeck A, Cocquerel L, Wychowski C, Cacan R, Dubuisson J (February 2002). "Glycosylation of the hepatitis C virus envelope protein E1 occurs posttranslationally in a mannosylphosphoryldolichol-deficient CHO mutant cell line". Glycobiology. 12 (2): 95–101. doi:10.1093/glycob/12.2.95. PMID 11886842.
^ abKnauer R, Lehle L (January 1999). "The oligosaccharyltransferase complex from yeast". Biochim. Biophys. Acta. 1426 (2): 259–73. doi:10.1016/S0304-4165(98)00128-7. PMID 9878773.
^Dempski RE, Imperiali B (December 2002). "Oligosaccharyl transferase: gatekeeper to the secretory pathway". Curr Opin Chem Biol. 6 (6): 844–50. doi:10.1016/S1367-5931(02)00390-3. PMID 12470740.
^Nilsson I, Kelleher DJ, Miao Y, Shao Y, Kreibich G, Gilmore R, von Heijne G, Johnson AE (May 2003). "Photocross-linking of nascent chains to the STT3 subunit of the oligosaccharyltransferase complex". J. Cell Biol. 161 (4): 715–25. doi:10.1083/jcb.200301043. PMC2199356. PMID 12756234.
^Karaoglu D, Kelleher DJ, Gilmore R (October 2001). "Allosteric regulation provides a molecular mechanism for preferential utilization of the fully assembled dolichol-linked oligosaccharide by the yeast oligosaccharyltransferase". Biochemistry. 40 (40): 12193–206. doi:10.1021/bi0111911. PMID 11580295.
^Imperiali B (November 1997). "Protein Glycosylation: The Clash of the Titans". Accounts of Chemical Research. 30 (11): 452–459. doi:10.1021/ar950226k.
^Ruiz-Canada C, Kelleher DJ, Gilmore R (January 2009). "Cotranslational and posttranslational N-glycosylation of polypeptides by distinct mammalian OST isoforms". Cell. 136 (2): 272–83. doi:10.1016/j.cell.2008.11.047. PMC2859625. PMID 19167329.
^Lizak C, Gerber S, Numao S, Aebi M, Locher KP (June 2011). "X-ray structure of a bacterial oligosaccharyltransferase". Nature. 474 (7351): 350–5. doi:10.1038/nature10151. PMID 21677752. S2CID 205225231.
^Marquardt T, Denecke J (June 2003). "Congenital disorders of glycosylation: review of their molecular bases, clinical presentations and specific therapies". Eur. J. Pediatr. 162 (6): 359–79. doi:10.1007/s00431-002-1136-0. PMID 12756558. S2CID 3196550.
External linksedit
oligosaccharyltransferase at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
oligosaccharyltransferase, membrane, protein, complex, that, transfers, sugar, oligosaccharide, from, dolichol, nascent, protein, type, glycosyltransferase, sugar, glc3man9glcnac2, where, glucose, mannose, glcnac, acetylglucosamine, attached, asparagine, resid. Oligosaccharyltransferase or OST EC 2 4 1 119 is a membrane protein complex that transfers a 14 sugar oligosaccharide from dolichol to nascent protein It is a type of glycosyltransferase The sugar Glc3Man9GlcNAc2 where Glc Glucose Man Mannose and GlcNAc N acetylglucosamine is attached to an asparagine Asn residue in the sequence Asn X Ser or Asn X Thr where X is any amino acid except proline This sequence is called a glycosylation sequon The reaction catalyzed by OST is the central step in the N linked glycosylation pathway STT3Structure of yeast OST 1 IdentifiersSymbolSTT3PfamPF02516Pfam clanCL0111InterProIPR003674OPM superfamily242OPM protein3rceCAZyGT66Membranome275Available protein structures Pfam structures ECOD PDBRCSB PDB PDBe PDBjPDBsumstructure summary Contents 1 Location 2 Structure and function 3 Clinical significance 4 See also 5 References 6 External linksLocation edit nbsp ER Translocon complex 2 Many protein complexes are involved in protein synthesis The actual production takes place in the ribosomes grey and light blue Through the ER translocon green Sec61 blue TRAP complex and red oligosaccharyl transferase complex the newly synthesized protein is transported across the membrane gray into the interior of the ER Sec61 is the protein conducting channel and the OST adds sugar moieties to the nascent protein OST is a component of the translocon in the endoplasmic reticulum ER membrane A lipid linked core oligosaccharide is assembled at the membrane of the endoplasmic reticulum and transferred to selected asparagine residues of nascent polypeptide chains by the oligosaccharyl transferase complex 3 The active site of OST is located about 4 nm from the lumenal face of the ER membrane 4 It usually acts during translation as the nascent protein is entering the ER but this cotranslational glycosylation is nevertheless called a posttranslational modification A few examples have been found of OST activity after translation is complete 5 6 Current opinion is that post translational activity may occur if the protein is poorly folded or folds slowly 6 Structure and function editYeast OST is composed of eight different membrane spanning proteins in three subcomplexes one of them is OST4 7 8 These octomers do not form higher order oligomers and three of the eight proteins are glycosylated themselves 7 OST in mammals is known to have a similar composition 9 10 OST is thought to require many subunits because it must 11 Position itself near the translocon pore Recognize and bind oligosaccharyldolichol Scan the nascent protein in order to recognize and bind sequons Move these two large substrates into their proper locations and conformations Activate the Asn amide nitrogen atom for the actual transfer of oligosaccharide Release its substrates The catalytically active subunit of the OST is called STT3 Two paralogs exist in eukaryotes termed STT3A and STT3B STT3A is primarily responsible for cotranslational glycosylation of the nascent polypeptide as it enters the lumen of the endoplasmic reticulum whereas STT3B can also mediate posttranslational glycosylation 12 The structure of PglB the prokaryotic homolog of STT3 has been solved 13 The high sequence similarity between the prokaryotic and the eukaryotic STT3 suggests that their structures are similar Clinical significance editCDG syndromes are genetic disorders of the glycosylation pathway They are labelled Type I if the defective gene is for an enzyme involved in the assembly or transfer of the Glc3Man9GlcNAc2 dolichol precursor They are labelled Type II if the defective step occurs after the action of OST in the N linked glycosylation pathway or involves O linked glycosylation 14 See also editSTT3A STT3BReferences edit Wild R Kowal J Eyring J Ngwa EM Aebi M Locher KP 2018 Structure of the yeast oligosaccharyltransferase complex gives insight into eukaryotic N glycosylation Science 359 6375 545 550 Bibcode 2018Sci 359 545W doi 10 1126 science aar5140 hdl 20 500 11850 228327 PMID 29301962 Pfeffer S Dudek J Gogala M Schorr S Linxweiler J Lang S Becker T Beckmann R Zimmermann R Forster F 2014 Structure of the mammalian oligosaccharyl transferase complex in the native ER protein translocon Nat Commun 5 5 3072 Bibcode 2014NatCo 5 3072P doi 10 1038 ncomms4072 PMID 24407213 Zufferey R Knauer R Burda P Stagljar I te Heesen S Lehle L Aebi M October 1995 STT3 a highly conserved protein required for yeast oligosaccharyl transferase activity in vivo EMBO J 14 20 4949 60 doi 10 1002 j 1460 2075 1995 tb00178 x PMC 394598 PMID 7588624 Nilsson IM von Heijne G March 1993 Determination of the distance between the oligosaccharyltransferase active site and the endoplasmic reticulum membrane J Biol Chem 268 8 5798 801 doi 10 1016 S0021 9258 18 53389 5 PMID 8449946 Pless DD Lennarz WJ Lennarz January 1977 Enzymatic conversion of proteins to glycoproteins Proc Natl Acad Sci U S A 74 1 134 8 Bibcode 1977PNAS 74 134P doi 10 1073 pnas 74 1 134 PMC 393212 PMID 264667 a b Duvet S Op De Beeck A Cocquerel L Wychowski C Cacan R Dubuisson J February 2002 Glycosylation of the hepatitis C virus envelope protein E1 occurs posttranslationally in a mannosylphosphoryldolichol deficient CHO mutant cell line Glycobiology 12 2 95 101 doi 10 1093 glycob 12 2 95 PMID 11886842 a b Knauer R Lehle L January 1999 The oligosaccharyltransferase complex from yeast Biochim Biophys Acta 1426 2 259 73 doi 10 1016 S0304 4165 98 00128 7 PMID 9878773 Dempski RE Imperiali B December 2002 Oligosaccharyl transferase gatekeeper to the secretory pathway Curr Opin Chem Biol 6 6 844 50 doi 10 1016 S1367 5931 02 00390 3 PMID 12470740 Nilsson I Kelleher DJ Miao Y Shao Y Kreibich G Gilmore R von Heijne G Johnson AE May 2003 Photocross linking of nascent chains to the STT3 subunit of the oligosaccharyltransferase complex J Cell Biol 161 4 715 25 doi 10 1083 jcb 200301043 PMC 2199356 PMID 12756234 Karaoglu D Kelleher DJ Gilmore R October 2001 Allosteric regulation provides a molecular mechanism for preferential utilization of the fully assembled dolichol linked oligosaccharide by the yeast oligosaccharyltransferase Biochemistry 40 40 12193 206 doi 10 1021 bi0111911 PMID 11580295 Imperiali B November 1997 Protein Glycosylation The Clash of the Titans Accounts of Chemical Research 30 11 452 459 doi 10 1021 ar950226k Ruiz Canada C Kelleher DJ Gilmore R January 2009 Cotranslational and posttranslational N glycosylation of polypeptides by distinct mammalian OST isoforms Cell 136 2 272 83 doi 10 1016 j cell 2008 11 047 PMC 2859625 PMID 19167329 Lizak C Gerber S Numao S Aebi M Locher KP June 2011 X ray structure of a bacterial oligosaccharyltransferase Nature 474 7351 350 5 doi 10 1038 nature10151 PMID 21677752 S2CID 205225231 Marquardt T Denecke J June 2003 Congenital disorders of glycosylation review of their molecular bases clinical presentations and specific therapies Eur J Pediatr 162 6 359 79 doi 10 1007 s00431 002 1136 0 PMID 12756558 S2CID 3196550 External links editoligosaccharyltransferase at the U S National Library of Medicine Medical Subject Headings MeSH Portal nbsp Biology Retrieved from https en wikipedia org w index php title Oligosaccharyltransferase amp oldid 1198290105, wikipedia, wiki, book, books, library,
