Figure 4.

Schematic diagrams of a type IV pilus (T4P), with and without the application of a stretching force. In (a), the relaxed form of the T4P (PDB entry 2HIL, rendered using MacPyMol (Delano Scientific, San Carlos, CA)) (left) and, for simplicity, is also shown as three continuous, close-packed, intertwined helical strands (right). In (b), the application of a pulling force F to the ends of the T4P results in stretching of the three-helix molecule. In (c), a large value of F has resulted in the (hypothesized) release of two of the three strands such that a single strand carries the stretching force. To see this figure in color, go online.