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The Outer Membrane Protein Insertion Porin (OmpIP/Omp85) Family [Function: Biogenesis/Secretion] Seed alignment | Full alignment | Pfam Wiki page | TC-DB page

Transmembrane ß-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 &ß-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 ß-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 &ß-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 ß 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 ß-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 ß barrel domain -all the way from bacteria to humans. SAM50 forms a 16-strands ß 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 ß strands were also predicted by PRED-TMBB2.

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Literature references

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SAM50, a side door to the mitochondria: The case of cytotoxic proteases
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The gain-of-function allele bamA (E470K) bypasses the essential requirement for BamD in ß-barrel outer membrane protein assembly
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Crystallization and X-ray analysis of Borrelia burgdorferi ß-barrel assembly machinery A
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Characterization of BamA reconstituted into a solid-supported lipid bilayer as a platform for measuring dynamics during substrate protein assembly into the membrane
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Membrane protein insertion through a mitochondrial ß-barrel gate
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Identification of new channels by systematic analysis of the mitochondrial outer membrane
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Granzyme B enters the mitochondria in a Sam50-, Tim22- and mtHsp70-dependent manner to induce apoptosis
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Mitochondrial-bacterial hybrids of BamA/Tob55 suggest variable requirements for the membrane integration of ß-barrel proteins
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Structural insight into the biogenesis of ß-barrel membrane proteins
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Characterization of the insertase for ß-barrel proteins of the outer mitochondrial membrane
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High-resolution structure of a new crystal form of BamA POTRA4-5 from Escherichia coli
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Structure and evolution of mitochondrial outer membrane proteins of beta-barrel topology
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The peripheral membrane subunits of the SAM complex function codependently in mitochondrial outer membrane biogenesis
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The N-terminal domain of Tob55 has a receptor-like function in the biogenesis of mitochondrial beta-barrel proteins
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Conserved pore-forming regions in polypeptide-transporting proteins
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Biogenesis of the Gram-negative bacterial outer membrane
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Omp85, an evolutionarily conserved bacterial protein involved in outer-membrane-protein assembly
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The Omp85 family of proteins is essential for outer membrane biogenesis in mitochondria and bacteria
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Evolutionary conservation of biogenesis of beta-barrel membrane proteins
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An essential role of Sam50 in the protein sorting and assembly machinery of the mitochondrial outer membrane
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POTRA: a conserved domain in the FtsQ family and a class of beta-barrel outer membrane proteins
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Proteins in this family with 3D-structure
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