Structural Research of Omp85-TpsB Outer Membrane Transporter Superfamily
The Omp85/TPS superfamily is a β-barrel protein found only in Gram-negative bacteria, chloroplasts, and mitochondrial outer membrane (OM). These proteins are called Toc75 in chloroplasts and Sam50 or Tob55 in mitochondria. These proteins catalyze beta-barrel protein insertion into the membrane and transmembrane translocation of the protein. Omp85/TPS family members play an important role in energy-dependent transport, protein secretion and input, protein automatic transport, lipid transport, and other physiological activities.
Progress in structural studies of the Omp85/TPS superfamily
Omp85/TPS proteins contain an amphiphilic β-folding layer, which forms a closed β-barrel structure and serves as a transmembrane structural domain. β-Barrels are 8-36 β-strands. The N-terminal part of the Omp85 superfamily consists of 1-7 repeats of soluble polypeptide transporter-associated (POTRA) structural domains with two α-helices and three β-folds. The C-terminus has a 16-stranded β-barrel pore that is highly conserved.
Action mechanism of the Omp85 protein BamA in bacteria
BamA is a highly conserved Omp85 protein in bacteria. It is an important component of the barrel assembly mechanism (BAM) that promotes the integration of beta-barrel proteins into OM. BamA secretes the exogenous protein TpsA. The TpsA protein is a virulence factor that folds into an extended beta-helix and is encoded in the same manipulator as its homologous TpsB transporter.
Figure 1. Structure of Omp85 protein superfamily members. (Doyle MT, et al., 2022)
| Protein | Organism | Method | Resolution | PDB Entry ID |
| BamA | Neisseria gonorrhoeae FA 1090 | X-ray diffraction | 3.2 Å | 4K3B |
| Outer membrane protein insertase BamA with one POTRA domain. | Escherichia coli | X-ray diffraction | 3 Å | 4C4V |
| BamA lacking POTRA domains 1-3 | [Haemophilus] ducreyi | X-ray diffraction | 2.913 Å | 4K3C |
| BamA-mediate Outer Membrane Protein Biogenesis | Escherichia coli K-12 | X-ray diffraction | 2.604 Å | 4N75 |
| BamB and BamA P3-5 complex | Escherichia coli K-12 | X-ray diffraction | 2.15 Å | 4XGA |
| A membrane complex | Escherichia coli K-12 | X-ray diffraction | 3.555 Å | 5AYW |
| BamABCDE complex, outer membrane beta-barrel assembly machinery entire complex | Escherichia coli | X-ray diffraction | 2.9 Å | 5D0O |
| BamACDE complex, outer membrane beta-barrel assembly machinery (BAM) complex | Escherichia coli | X-ray diffraction | 3.5 Å | 5D0Q |
| BamACDE subcomplex | Escherichia coli | X-ray diffraction | 3.392 Å | 5EKQ |
| BamA | Salmonella enterica subsp. enterica serovar Typhimurium str. LT2 | X-ray diffraction | 2.92 Å | 5OR1 |
| BamA beta-barrel with a C-terminal extension | Escherichia coli O157:H7 | X-ray diffraction | 2.6 Å | 6FSU |
| BamA POTRA4 | Haemophilus influenzae | X-ray diffraction | 2.03 Å | 6IZS |
| BamA POTRA3-5 | Haemophilus influenzae | X-ray diffraction | 2.03 Å | 6IZT |
| BamA POTRA1-4 | Haemophilus influenzae | X-ray diffraction | 3 Å | 6J09 |
| BAM complex | Escherichia coli K-12 | X-ray diffraction | 3.19 Å | 6LYQ |
| BAM complex | Escherichia coli K-12 | X-ray diffraction | 3.28 Å | 6LYR |
| BAM complex | Escherichia coli K-12 | X-ray diffraction | 3.05 Å | 6LYS |
| BAM complex | Escherichia coli K-12 | X-ray diffraction | 4.2 Å | 6LYU |
| BamA beta-barrel in complex with nanobody E6 | Escherichia coli O157:H7 | X-ray diffraction | 1.938 Å | 6QGW |
| BamABCDE in MSP1D1 nanodisc | Escherichia coli | Cryo-EM single particle analysis | 6.65 Å | 6SMX |
| BamABCDE in MSP1D1 nanodisc ensemble 0-1 | Escherichia coli | Cryo-EM single particle analysis | 10.8 Å | 6SN0 |
| BamABCDE in MSP1D1 nanodisc ensemble 0-2 | Escherichia coli | Cryo-EM single particle analysis | 9.5 Å | 6SN2 |
| BamABCDE in MSP1D1 nanodisc ensemble 1-2 | Escherichia coli | Cryo-EM single particle analysis | 10.5 Å | 6SO7 |
| R450A mutant of the membrane protein FhaC | Bordetella pertussis | X-ray diffraction | 3.5 Å | 3NJT |
| Membrane Transporter FhaC | Bordetella pertussis Tohama I | X-ray diffraction | 2.9 Å | 4QKY |
Table 1. Structural research of mp85-TpsB outer membrane transporter superfamily.
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References
- Doyle MT, et al. Function of the Omp85 Superfamily of Outer Membrane Protein Assembly Factors and Polypeptide Transporters. Annu Rev Microbiol. 2022. 76:259-279.
- Simmerman RF, et al. Structure and function of POTRA domains of Omp85/TPS superfamily. Int Rev Cell Mol Biol. 2014. 308:1-34.
