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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







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