Molecule of the Month: Pilus Machine
A molecular machine with a rotary motor builds a long protein filament involved in bacterial motility and attachment.
Cells in Motion
Exploring the Structure
Type IV Pilus
The pilin subunit has a distinctive structure. It has a globular head that is covered with charged, water-soluble amino acids (shown here in magenta), and a long alpha-helical tail that is mostly hydrophobic (shown in white). The hydrophobic tail plays two roles: it embeds the individual pilin subunits into the bacterial membrane, and it forms a tight bundle with other pilin subunits to stabilize the filament. To explore of pilin and the filament (PDB entry 2hil) in more detail, click on the image for an interactive JSmol.
Topics for Further Discussion
- A structural model was also obtained for an empty form of the machine, before it starts construction of the pilus. You can view it in PDB entry 3jc9.
- Structures for many other types of pili are available in the PDB archive—try searching for “pilus” to find them.
Related PDB-101 Resources
- Browse Molecular Motors
- Browse Molecular Infrastructure
- Browse Integrative/Hybrid Methods
- Browse Infectious Disease
- MK Hospenthal, TRD Costa & G Waksman (2017) A comprehensive guide to pilus biogenesis in gram-negative bacteria. Nature Reviews Microbiology 15, 365-379.
- M McCallum, S Tammam, A Khan, LL Burrows & PL Howell (2017) The molecular mechanism of the type IVa pilus motors. Nature Communications 8, 15091.
- 3jc8: YW Chang, LA Rettberg, A Treuner-Lange, J Iwasa, L Sogaard-Andersen & GJ Jensen (2016) Architecture of the type IVa pilus machine. Science 351, aad2001.
- 2hil: L Craig, N Volkmann, AS Arvai, ME Pique, M Yeager, EH Egelman & JA Tainer (2006) Type IV pilus structure by cryo-electron microscopy and crystallography: implications for pilus assembly and functions. Molecular Cell 23, 651-662.
July 2017, David Goodselldoi:10.2210/rcsb_pdb/mom_2017_7