PilT as the rod like motor protein sits at the bottom of TFP filament. In order to move, it may be required to bind to other components of TFP, such as PilQ, or to its own C-ring in the periplasmic space (Additional file 1: Figure 1A). This likely happens in the early stages of TFP assembly during retractions, when PilT is free to move. However, as TFP growth progresses, both PilQ and the C-ring have been incorporated into the TFP, and so do PilT and the motor. The binding of PilT to components of TFP may increase its activity or its stability. PilT interaction with PilQ may enhance the interaction between the C-ring and the periplasmic surface of the PB while interaction with the C-ring may increase the pilus extension rate. Based on our observations on the apoptosis inhibitory activity of the PB, we speculate that the interaction of PilT with PilQ or the C-ring may enhance the TFP extension force. We propose that during the retraction process, the force generated by the pilus motor can be transmitted to the periplasmic surface of the PB as a result of the binding of PilT to the pilus components. This may weaken the interaction of the C-ring and the periplasmic surface of the PB, which may activate the apoptosis signal pathway once the binding force approaches a certain level. Our model study provides valuable insights into the PilT motor activity in TFP and may help to design novel drug targets to prevent unwanted TFP filament formation.
We speculate that the macromolecules or macromolecular complexes formed within the periplasm can provide more effective drug screening platforms. Our earlier study suggested that part of the pilus extension force is a result of the reaction forces between the periplasm and the pilus in situ polymerized within the periplasm . Thus, we speculate that the formation of a specific complex with the pilus assembly site may enhance the drug screening platforms and minimize the drug specificity and toxicity. This may provide an alternative drug screening system via a host of macromolecular complexes formed in the periplasm. d2c66b5586