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User:Ke Xiao/Geobacter pilus models

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Scientific Reports an online, open access journal: nature.com/srep


Low energy atomic models suggesting a pilus structure that could account for electrical conductivity of Geobacter sulfurreducens pili.
Ke Xiao, Nikhil S. Malvankar, Chuanjun Shu, Eric Martz, Derek R. Lovley, and Xiao Sun.
Scientific Reports, March 2016: nature.com/articles/srep23385. (DOI: 10.1038/srep23385)

Molecular TourMolecular Tour

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Pilus Model

The theoretical Geobacter sulfurreducens pilus model shown here, called ARC-1[1] (), is representative of a cluster of 50 low-energy models with an arrangement of aromatic rings consistent with X-ray diffraction data[2]. Unlike the docking of crystallographic models into electron density from cryo-electron microscopy[3][4], these models have chemically realistic interactions between subunit chains. Energy minimization produced subunit interactions with shape complementarity, non-covalent bonds, and very few atomic clashes[5].

Monomer Chains

This ARC-1 model contains 21 chains of pilA[6] of Geobacter sulfurreducens. The 21 chains were restrained to have . Amino acids 3-50 are . Modeling was initiated with model 1 of NMR ensemble 2m7g of Geobacter sulfurreducens. The monomers in ARC-1 are only slightly different from the initial conformation:

  • : 2m7g model 1, ARC-1 chain K.
  • .

Stacked Aromatic Rings

The ARC-1 model (and others of its cluster) are the first chemically realistic pilus models that can account for the electrical conductivity of these pili in terms of a core of stacked aromatic rings. These models are consistent with multiple lines of experimental evidence including X-ray diffraction suggesting stacked aromatics[1][2].

Each pilA chain contains . In the pilus assembly, .

The aromatic . The core aromatic rings are .

Salt Bridges

80% of the 50 lowest-energy models have a salt bridge between Arg41 and Asp39 in different chains.

  • (Arg41:Asp39, sidechain nitrogens and oxygens).
  • .

Monomers Per Turn

The ARC-1 model has 6.4 monomer chains per turn (56.0 degrees rotation between monomers). This is more chains/turn than some previous type IV pilus models. Among the 50 models with lowest energy in the cluster including ARC-1, chains/turn ranged from 5.0 to 7.6.

To visualize chains/turn, we show (alpha carbon of Phe51). Then these chain-marking-atoms are , and the resulting helix is viewed from one end. When counting the chains/turn, bear in mind that the first and last (to complete one turn) count as 1/2 chain each.

Pilus

Chains/Turn (Angle)

Image

Geobacter sulfurreducens (type IVa, 61 amino acids, theoretical model ARC-1, 2016)[1]

6.4 (56.0°)

 

Pseudomonas aeruginosa (type IVa, 150 amino acids, fiber diffraction, 2004)[7]

4.0 (90°)

 

Vibrio cholerae (type IVb, 198 amino acids, cryo-EM, 2012)[8]

3.7 (96.8°)

 

Neisseria gonorrhoeae (type IVa, 165 amino acids, cryo-EM 2hil, 2006)[9]

3.6 (100.8°)

 


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Theoretical Model: The protein structure described on this page was determined theoretically, and hence should be interpreted with caution.


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Notes & ReferencesNotes & References

  1. ↑ 1.0 1.1 1.2 Xiao et al., Scientific Reports, March 2016: nature.com/articles/srep23385.
  2. ↑ 2.0 2.1 Malvankar NS, Vargas M, Nevin K, Tremblay PL, Evans-Lutterodt K, Nykypanchuk D, Martz E, Tuominen MT, Lovley DR. Structural basis for metallic-like conductivity in microbial nanowires. MBio. 2015 Mar 3;6(2):e00084. doi: 10.1128/mBio.00084-15. PMID:25736881 doi:http://dx.doi.org/10.1128/mBio.00084-15
  3. ↑ Craig L, Volkmann N, Arvai AS, Pique ME, Yeager M, Egelman EH, Tainer JA. Type IV pilus structure by cryo-electron microscopy and crystallography: implications for pilus assembly and functions. Mol Cell. 2006 Sep 1;23(5):651-62. PMID:16949362 doi:10.1016/j.molcel.2006.07.004
  4. ↑ Craig L, Taylor RK, Pique ME, Adair BD, Arvai AS, Singh M, Lloyd SJ, Shin DS, Getzoff ED, Yeager M, Forest KT, Tainer JA. Type IV pilin structure and assembly: X-ray and EM analyses of Vibrio cholerae toxin-coregulated pilus and Pseudomonas aeruginosa PAK pilin. Mol Cell. 2003 May;11(5):1139-50. PMID:12769840
  5. ↑ The chemical realism of these theoretical energy-minimized models contrasts with models where empirical monomer structures are docked into cryo-electron microscopic electron density maps. Those are unrealistic in details of subunit interactions, lacking shape complementarity and having many atomic clashes. See "Initial Model Outputs" in the publication for details.
  6. ↑ Each chain contains the 61 C-terminal amino acids of UniProt Q74D23.
  7. ↑ Craig L, Pique ME, Tainer JA. Type IV pilus structure and bacterial pathogenicity. Nat Rev Microbiol. 2004 May;2(5):363-78. PMID:15100690 doi:http://dx.doi.org/10.1038/nrmicro885
  8. ↑ Li J, Egelman EH, Craig L. Structure of the Vibrio cholerae Type IVb Pilus and stability comparison with the Neisseria gonorrhoeae type IVa pilus. J Mol Biol. 2012 Apr 20;418(1-2):47-64. doi: 10.1016/j.jmb.2012.02.017. Epub 2012, Feb 21. PMID:22361030 doi:http://dx.doi.org/10.1016/j.jmb.2012.02.017
  9. ↑ Craig L, Volkmann N, Arvai AS, Pique ME, Yeager M, Egelman EH, Tainer JA. Type IV pilus structure by cryo-electron microscopy and crystallography: implications for pilus assembly and functions. Mol Cell. 2006 Sep 1;23(5):651-62. PMID:16949362 doi:10.1016/j.molcel.2006.07.004
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