Biology:Bam A
| OMP insertion (BamComplex) porin | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | BamA | ||||||||
| Pfam | PF01103 | ||||||||
| InterPro | IPR023707 | ||||||||
| TCDB | 1.B.33 | ||||||||
| OPM superfamily | 179 | ||||||||
| OPM protein | 5ayw | ||||||||
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BamA is a β-barrel, outer membrane protein found in Gram-negative bacteria and it is the main and vital component of the β-barrel assembly machinery (BAM) complex in those bacteria.[1] BAM Complex consists of five components; BamB, BamC, BamD, BamE (all are lipoproteins) and BamA (Outer membrane protein).[2][3][4][5] This complex is responsible in catalyzing folding and insertion of β-barrel proteins into the outer membrane of Gram-negative bacteria.[6][7]
β-barrel membrane proteins can only be found in the outer membrane of Gram-negative bacteria and in organelles such as mitochondria and chloroplasts which were evolved from bacteria.[8][9] In Gram-negative bacteria, outer membrane proteins are synthesized in the cytoplasm and then exported into the periplasm by Sec translocon machinery.[10] Then they are escorted to the inner surface of the outer membrane by molecular chaperons. Finally those nascent proteins interact with BAM Complex and insert into the outer membrane as β-barrel proteins.[11]
Structure and function
According to the fully resolved BamA structure of N. gonorrhoeae, BamA has a large periplasmic domain connected to a transmembrane β-barrel domain which is made of 16 antiparallel β strands.[12] There are five polypeptide translocation-associated (POTRA) domains extending from the barrel at the periplasmic domain of BamA. Current studies suggest that the four lipoproteins in the BAM Complex (BamB, BamC, BamD, BamE ) assemble on to the POTRA domains of BamA, making it the vital component of BAM Complex. The first and the last or 16th β-strands associate in closing the barrel. Extracellular loops (eL) eL4, eL6 and eL7 of the barrel forms a dome over the barrel by isolating the interior of the barrel from the extracellular space and interior of the BamA barrel is completely empty.
The external rim of the β-barrel has a narrow, reduced hydrophobic surface and it reduces lipid order and thickness of the membrane around the barrel. Transient separation of 1st and 16th β-strands which are associated in closing the barrel causes lateral opening of the barrel making a route from interior cavity of the BamA into the outer membrane. POTRA 5 domain of BamA sits close to the β–barrel and interacts with periplasmic loops (pL) pL3, pL4, pL5, pL7 and stabilize the closed conformation of the barrel. Swing movements of POTRA 5 domain and having no interactions with pLs make the opening of the barrel. Thus POTRA domains act as a gate to regulate the access into the interior of β–barrel. Hence there are three structural features associate with BamA that regulates the entry of β-barrel proteins into the outer membrane. First, open and closed conformation of BamA β-barrel. Second, the narrow and reduced hydrophobic rim on the surface of the β –barrel causes local destabilization of the outer membrane. Third, ability to undergo lateral opening of the barrel by transient separation of 1st and 16th β–barrel strands.
References
- ↑ "Biogenesis of beta-barrel membrane proteins in bacteria and eukaryotes: evolutionary conservation and divergence". Cellular and Molecular Life Sciences 66 (17): 2789–804. September 2009. doi:10.1007/s00018-009-0029-z. PMID 19399587.
- ↑ "The N-terminal domain of Tob55 has a receptor-like function in the biogenesis of mitochondrial beta-barrel proteins". The Journal of Cell Biology 176 (1): 77–88. January 2007. doi:10.1083/jcb.200602050. PMID 17190789.
- ↑ "Membrane protein architects: the role of the BAM complex in outer membrane protein assembly". Nature Reviews. Microbiology 7 (3): 206–14. March 2009. doi:10.1038/nrmicro2069. PMID 19182809.
- ↑ "β-Barrel membrane protein assembly by the Bam complex". Annual Review of Biochemistry 80: 189–210. 2011. doi:10.1146/annurev-biochem-061408-144611. PMID 21370981.
- ↑ "Making a beta-barrel: assembly of outer membrane proteins in Gram-negative bacteria". Current Opinion in Microbiology 15 (2): 189–93. April 2012. doi:10.1016/j.mib.2011.12.007. PMID 22221898.
- ↑ "From evolution to pathogenesis: the link between β-barrel assembly machineries in the outer membrane of mitochondria and gram-negative bacteria". International Journal of Molecular Sciences 13 (7): 8038–50. 2012. doi:10.3390/ijms13078038. PMID 22942688.
- ↑ "Assembly of outer-membrane proteins in bacteria and mitochondria". Microbiology (Reading, England) 156 (Pt 9): 2587–2596. September 2010. doi:10.1099/mic.0.042689-0. PMID 20616105.
- ↑ "Importing mitochondrial proteins: machineries and mechanisms". Cell 138 (4): 628–44. August 2009. doi:10.1016/j.cell.2009.08.005. PMID 19703392.
- ↑ "Evolution of the β-barrel assembly machinery". Trends in Microbiology 20 (12): 612–20. December 2012. doi:10.1016/j.tim.2012.08.006. PMID 22959613.
- ↑ "A new bioinformatics analysis tools framework at EMBL-EBI". Nucleic Acids Research 38 (Web Server issue): W695–9. July 2010. doi:10.1093/nar/gkq313. PMID 20439314.
- ↑ "Identification of a multicomponent complex required for outer membrane biogenesis in Escherichia coli". Cell 121 (2): 235–45. April 2005. doi:10.1016/j.cell.2005.02.015. PMID 15851030.
- ↑ "Structural insight into the biogenesis of β-barrel membrane proteins". Nature 501 (7467): 385–90. September 2013. doi:10.1038/nature12521. PMID 23995689.
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