Force-dependent polymorphism in type IV pili reveals hidden epitopes

Abstract

Through evolution, nature has produced exquisite nanometric structures, with features unrealized in the most advanced manmade devices. Type IV pili (Tfp) represent such a structure: 6-nmwide retractable filamentous appendages found in many bacteria, including human pathogens. Whereas the structure of Neisseria gonorrhoeae Tfp has been defined by conventional structural techniques, it remains difficult to explain the wide spectrum of functions associated with Tfp. Here we uncover a previously undescribed force-induced quaternary structure of the N. gonorrhoeae Tfp. By using a combination of optical and magnetic tweezers, atomic force microscopy, and molecular combing to apply forces on purified Tfp, we demonstrate that Tfp subjected to approximately 100 pN of force will transition into a new conformation. The new structure is roughly 3 times longer and 40% narrower than the original structure. Upon release of the force, the Tfp fiber regains its original form, indicating a reversible transition. Equally important, we show that the force-induced conformation exposes hidden epitopes previously buried in the Tfp fiber. We postulate that this transition provides a means for N. gonorrhoeae to maintain attachment to its host while withstanding intermittent forces encountered in the environment. Our findings demonstrate the need to reassess our understanding of Tfp dynamics and functions. They could also explain the structural diversity of other helical polymers while presenting a unique mechanism for polymer elongation and exemplifying the extreme structural plasticity of biological polymers.force polymorphism | alternate immunogenic properties

The Structure of the CS1 Pilus of Enterotoxigenic Escherichia coli Reveals Structural Polymorphism

“…Yet Vibrio cholerae type IV pili are heterogeneous even without being subjected to mechanical shearing (44), and Neisseria gonorrhoeae type IV pili are not polymorphic although they were prepared by shearing (45). Interestingly, the N. gonorrhoeae type IV pili were shown to undergo a conformational change that exposed new epitopes when force was applied (46). Filament polymorphism implies structural plasticity, which would allow the pili to maintain adherence to the host epithelium when subjected to high flow forces.…”

Type IV pili mechanochemically regulate virulence factors in Pseudomonas aeruginosa

“…In Neisseria gonorrhea, TFP exhibit conformational changes upon stretching (28) and stretching reduces TFP width. Interestingly, these changes expose hidden PilA epitopes, indicating that PilA itself may change conformation upon tension.…”

Type IV Pilin Proteins: Versatile Molecular Modules

“…In some cases, the deformations occur in localized regions, implying that there are multiple types of interactions that can occur between pilin subunits in a single intact fiber. The ability to stretch without breaking was suggested to provide a buffer against force fluctuations along the length of a fiber, preventing detachment during transient increases in shear forces (46). The ability to undergo deformation was recently linked to the presence of the Neisseria-specific minor pilin, PilX (63).…”

“…Interestingly, Biais and colleagues (46) demonstrated that the T4a pili of N. gonorrhoeae can undergo dramatic and reversible conformational changes upon application of threshold levels of force, stretching in their longer dimension to become ϳ40% narrower than unstretched pili, with a concomitant reduction of ϳ2/3 of the mass per unit length (Fig. 6).…”