A Highly Dynamic Loop of the Pseudomonas aeruginosa PA14 Type IV Pilin Is Essential for Pilus Assembly

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Type IVa pili (T4aP) are essential surface structures in bacteria like Pseudomonas aeruginosa, mediating critical functions including attachment and virulence.
• Pseudomonas aeruginosa is an opportunistic pathogen, and its T4aP are significant virulence factors, contributing to hospital-acquired infections.

Purpose of the Study:

• To determine the backbone resonance assignment of the C-terminal domain of group III PilA from the highly virulent Pseudomonas aeruginosa strain PA14.
• To investigate the structural dynamics and their role in pilus assembly and stability.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy for backbone resonance assignment.
• Analysis of chemical shifts to predict secondary structure probabilities.
• Homology modeling using a group V pilin structural template.

Main Results:

• The C-terminal domain of group III PilA from P. aeruginosa PA14 was assigned.
• High microsecond-millisecond dynamics were observed in the distal segment of the αβ loop.
• Internal deletion in this segment impaired pilus assembly, indicating a dominant negative effect.

Conclusions:

• The observed dynamics in the αβ loop suggest a critical role in pilin polymerization and T4aP assembly.
• Specific pilin conformations balancing hydrophobic core interactions and hydrophilic surface loops are likely necessary for stable filament formation.