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The Outer Membrane Protein Insertion Porin (OmpIP/Omp85) Family [Function: Biogenesis/Secretion] Seed alignment | Full alignment in OMPdb | |
Transmembrane β-barrels are synthesized in the cytoplasm and transferred through the inner membrane using the Sec system. In the periplasmic space, chaperones such as SurA and Skp, bind these proteins and target them to the outer membrane. It is believed that the highly conserved Omp85 acts in vivo in a way that facilitates the correct folding and the insertion of other β-barrels in the outer membrane. The conserved domain in Omp85 is also sometimes referred to as Bacterial Surface Antigen D15 and homologs are also found in mitochondria (Sam50/Tob55) and chloroplasts (OEP75). The transmembrane domain (composed of 16 beta-strands), is located in the C-terminus whereas, in the N-terminus, Omp85 possesses 5 conserved POTRA (Polypeptide Transport) domains. These domains are believed to interact with the transferred β-barrel and the final insertion into the outer membrane is performed with lateral diffusion. Conserved motifs that are believed to be parts of the pore-forming region are also found in all members of this family. The SAM complex plays a vital role in the integration of beta barrel proteins into the outer membrane. It consists of SAM50 and two peripheral proteins, SAM35 and SAM37. SAM50 features a single non-membrane polypeptide-transport-associated (POTRA) domain that is not crucial for cell viability and, also, a conserved loop six, which promotes beta-signal binding of the pre-proteins to the lateral gate and insertion of next hairpins into the outer membrane. Biochemical studies revealed that SAM50 has a conserved beta barrel domain -all the way from bacteria to humans. SAM50 forms a 16-strands beta barrel in the mitochondrial outer membrane, which has a N-terminal POTRA domain exposed into the intermembrane space, whereas the bacterial counterparts are known to possess a 16-stranded barrel, information that is experimentally verified since four members of the OmpIP/Omp85 family have experimentally determined 3D. 16 beta strands were also predicted by PRED-TMBB2. | |
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Literature references | |
Biogenesis of the Gram-negative bacterial outer membrane Curr Opin Microbiol. 2004 Dec;7(6):610-6. doi: 10.1016/j.mib.2004.10.011. PMID: 15556033 | |
Omp85, an evolutionarily conserved bacterial protein involved in outer-membrane-protein assembly Res Microbiol. 2004 Apr;155(3):129-35. doi: 10.1016/j.resmic.2003.11.007. PMID: 15143770 | |
The Omp85 family of proteins is essential for outer membrane biogenesis in mitochondria and bacteria J Cell Biol. 2004 Jan 5;164(1):19-24. doi: 10.1083/jcb.200310092. Epub 2003 Dec 29. PMID: 14699090 | |
Evolutionary conservation of biogenesis of beta-barrel membrane proteins Nature. 2003 Dec 18;426(6968):862-6. doi: 10.1038/nature02208. PMID: 14685243 | |
Conserved pore-forming regions in polypeptide-transporting proteins FEBS J. 2005 Mar;272(6):1367-78. doi: 10.1111/j.1742-4658.2005.04569.x. PMID: 15752354 | |
Structure and function of an essential component of the outer membrane protein assembly machine Science. 2007 Aug 17;317(5840):961-4. doi: 10.1126/science.1143993. PMID: 17702946 | |
High-resolution structure of a new crystal form of BamA POTRA4-5 from Escherichia coli Acta Crystallogr Sect F Struct Biol Cryst Commun. 2011 Jul 1;67(Pt 7):734-8. doi: 10.1107/S1744309111014254. Epub 2011 Jun 23. PMID: 21795783 | |
Structure of BamA, an essential factor in outer membrane protein biogenesis Acta Crystallogr D Biol Crystallogr. 2014 Jun;70(Pt 6):1779-89. doi: 10.1107/S1399004714007482. Epub 2014 May 30. PMID: 24914988 | |
The structural basis of autotransporter translocation by TamA Nat Struct Mol Biol. 2013 Nov;20(11):1318-20. doi: 10.1038/nsmb.2689. Epub 2013 Sep 22. PMID: 24056943 | |
The N-terminal domain of Tob55 has a receptor-like function in the biogenesis of mitochondrial beta-barrel proteins J Cell Biol. 2007 Jan 1;176(1):77-88. doi: 10.1083/jcb.200602050. Epub 2006 Dec 26. PMID: 17190789 | |
Membrane protein insertion through a mitochondrial ?-barrel gate Science. 2018 Jan 19;359(6373):eaah6834. doi: 10.1126/science.aah6834. PMID: 29348211 | |
Characterization of the insertase for ?-barrel proteins of the outer mitochondrial membrane J Cell Biol. 2012 Nov 12;199(4):599-611. doi: 10.1083/jcb.201207161. Epub 2012 Nov 5. PMID: 23128244 | |
An essential role of Sam50 in the protein sorting and assembly machinery of the mitochondrial outer membrane J Biol Chem. 2003 Dec 5;278(49):48520-3. doi: 10.1074/jbc.C300442200. Epub 2003 Oct 21. PMID: 14570913 | |
Dissecting membrane insertion of mitochondrial beta-barrel proteins Cell. 2008 Mar 21;132(6):1011-24. doi: 10.1016/j.cell.2008.01.028. PMID: 18358813 | |
The peripheral membrane subunits of the SAM complex function codependently in mitochondrial outer membrane biogenesis Mol Biol Cell. 2008 Jan;19(1):126-36. doi: 10.1091/mbc.e07-08-0796. Epub 2007 Oct 31. PMID: 17978093 | |
Structural insight into the biogenesis of ?-barrel membrane proteins Nature. 2013 Sep 19;501(7467):385-90. doi: 10.1038/nature12521. Epub 2013 Sep 1. PMID: 23995689 | |
Mitochondrial-bacterial hybrids of BamA/Tob55 suggest variable requirements for the membrane integration of ?-barrel proteins Sci Rep. 2016 Dec 16;6:39053. doi: 10.1038/srep39053. PMID: 27982054 | |
POTRA: a conserved domain in the FtsQ family and a class of beta-barrel outer membrane proteins Trends Biochem Sci. 2003 Oct;28(10):523-6. doi: 10.1016/j.tibs.2003.08.003. PMID: 14559180 | |
Structure and evolution of mitochondrial outer membrane proteins of beta-barrel topology Biochim Biophys Acta. 2010 Jun-Jul;1797(6-7):1292-9. doi: 10.1016/j.bbabio.2010.04.019. Epub 2010 May 5. PMID: 20450883 | |
Proteins in this family with 3D-structure | |
Q5F5W8 | |
Q93PM2 | |
P0A940 | |
P0A942 | |
Q8ZRP0 | |
G2QFF9 |
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