High-Resolution Cryo-EM Structure of the Pseudomonas aeruginosa PAO1 Type IV Pilus Reveals Insights into Its Assembly and Architecture

Core Concepts

The cryo-EM structure of the Pseudomonas aeruginosa PAO1 Type IV pilus provides detailed insights into the molecular architecture and assembly of this important bacterial surface appendage involved in adhesion, motility, and biofilm formation.

Abstract

The study presents the high-resolution cryo-EM structure of the Type IV pilus (T4P) from the important human pathogen Pseudomonas aeruginosa PAO1 strain. T4Ps are filamentous surface structures that play crucial roles in bacterial adhesion, motility, and biofilm formation.
Key highlights:

The T4P exhibits a tubular architecture assembled from repeated PilA subunits, with an overall helical rise of 10.17 Å and a twist of 87.39° per subunit.
The PilA subunit adopts a classical pilin fold, featuring an extended N-terminal α-helix that forms the core of the pilus, and a C-terminal globular domain that coats the outer surface.
Hydrophobic interactions between the N-terminal α-helices and the globular domains stabilize the pilus structure.
Comparison with T4P structures from other bacterial species reveals both conserved architectural principles and distinct features, such as the relatively small diameter and lack of flexible surface loops in the P. aeruginosa T4P.
The structure provides a framework for understanding the molecular mechanisms underlying T4P-mediated surface sensing, adhesion, and biofilm formation in this major human pathogen.

Stats

The P. aeruginosa PAO1 T4P has a helical rise of 10.17 Å and a helical twist of 87.39° per subunit, resulting in an overall helical pitch of 41.89 Å.
The T4P has a diameter of approximately 51 Å.

Quotes

"The N-terminal helices constitute the pilus core where they stabilise the tubular assembly via hydrophobic interactions."
"The globular C-terminal pilin domain contains a β-sheet consisting of four β-strands that face the exterior of the T4P and are thus exposed to the solvent."
"The comparatively small diameter is remarkable when combined with the observation that the P. aeruginosa T4P does not present flexible loops on the outer surface of the pilus, which are observed prominently in the structures of other pili."

Key Insights Distilled From

Structure of the Pseudomonas aeruginosa PAO1 Type IV pilus

by Ochner,H., B... at www.biorxiv.org 04-09-2024

https://www.biorxiv.org/content/10.1101/2024.04.09.588664v1

Deeper Inquiries

How do the structural features of the P. aeruginosa T4P, such as its small diameter and lack of flexible surface loops, contribute to its functional roles in adhesion, motility, and biofilm formation?

The structural features of the P. aeruginosa T4P play a crucial role in its functional roles in adhesion, motility, and biofilm formation. The small diameter of the T4P, which is the smallest among the compared structures, contributes to its unique properties. The compact nature of the pilus allows for tight packing of the N-terminal α-helices in the core of the pilus, providing stability and strength to the structure. This tight packing is essential for the pilus to withstand mechanical forces during processes like twitching motility, where the pilus extends and retracts to facilitate movement on surfaces.
Additionally, the lack of flexible surface loops on the outer surface of the P. aeruginosa T4P is significant for its function in adhesion and biofilm formation. Flexible loops on the surface of pili are often targets for extracellular proteases, which can degrade the pilus and compromise its function. By lacking these flexible loops, the P. aeruginosa T4P is more resistant to proteolysis, making it more robust and durable in various environmental conditions. This resistance to degradation enhances the pilus's ability to mediate adhesion to surfaces and form stable biofilms, which are critical for bacterial colonization and persistence.
In summary, the small diameter and lack of flexible surface loops in the P. aeruginosa T4P contribute to its structural integrity, mechanical strength, and resistance to proteolysis, enabling its essential functions in adhesion, motility, and biofilm formation.

What are the potential implications of the T4P structure for the development of strategies to combat antibiotic-resistant P. aeruginosa infections?

The detailed structural insights provided by the T4P structure of P. aeruginosa have significant implications for the development of strategies to combat antibiotic-resistant infections caused by this pathogen. Understanding the molecular architecture of the T4P can guide the design of novel therapeutic approaches that target specific components of the pilus assembly and function.
One potential implication is the development of inhibitors that disrupt the assembly or stability of the T4P. By targeting key interactions within the pilus structure, such inhibitors could prevent the formation of functional pili, thereby compromising the pathogen's ability to adhere to surfaces, form biofilms, and establish infections. This approach could be particularly effective in combating antibiotic-resistant strains of P. aeruginosa that rely heavily on T4P-mediated mechanisms for virulence and persistence.
Furthermore, the structural information on the T4P could inspire the design of vaccines or immunotherapies that target specific epitopes on the pilus surface. By eliciting an immune response against the pilus, these strategies could prevent bacterial attachment, colonization, and biofilm formation, ultimately reducing the severity and spread of P. aeruginosa infections.
Overall, the T4P structure provides a foundation for the development of innovative therapeutic interventions that specifically target the virulence factors of P. aeruginosa, offering new avenues for combating antibiotic resistance and improving treatment outcomes for infections caused by this pathogen.

What other cellular components, such as the Type IV secretion system, interact with the T4P and how do these interactions influence the assembly and function of the pilus?

The Type IV secretion system (T4SS) is a critical cellular component that interacts with the T4P in P. aeruginosa, influencing the assembly and function of the pilus. The T4SS is responsible for the secretion of proteins, DNA, and other molecules across the bacterial cell envelope, playing a key role in virulence, genetic exchange, and intercellular communication.
In the context of T4P, the T4SS is involved in the biogenesis and regulation of the pilus assembly. The T4SS machinery in the periplasm of P. aeruginosa interacts with the base of the T4P filament, facilitating the secretion and assembly of pilin subunits into the growing pilus structure. This interaction is essential for the proper formation and stability of the pilus, ensuring that it can perform its functions in adhesion, motility, and biofilm formation effectively.
Moreover, the T4SS may also play a role in the delivery of effector molecules or virulence factors through the T4P during interactions with host cells or other bacteria. By coordinating the activities of the T4P and T4SS, P. aeruginosa can modulate its surface sensing, adhesion, and pathogenicity mechanisms, enhancing its ability to colonize host tissues and evade immune responses.
Overall, the interaction between the T4P and the T4SS in P. aeruginosa is a coordinated process that influences the assembly, function, and virulence of the bacterium. Understanding these interactions at a molecular level is crucial for deciphering the complex mechanisms underlying P. aeruginosa pathogenicity and for developing targeted strategies to disrupt these processes for therapeutic purposes.