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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