Large-Scale Structural Dynamics in the Tail Fiber Modulate the Infective Transition of the T7 Bacteriophage.

Bacteriophages are gaining interest due to their potential use against multidrug-resistant bacteria. Here, we investigated the structural dynamics of T7 bacteriophage tail fibers. The T7 virion comprises an icosahedral protein shell and a tail-fiber complex, which is involved in bacterial target recognition and viral DNA injection. The virus has six L-shaped, ∼40-nm-long fibers connected to the tail-tube, which are thought to be essential for initial host recognition and, possibly, for surface exploration. By using high-speed atomic force microscopy (HS-AFM) and molecular dynamics (MD) simulations combined with small angle X-ray scattering (SAXS), we analyzed the molecular structure and movements of isolated tail fibers and tail-fiber complexes. We found that the kink region separating the proximal and distal sections of the fiber acts as a molecular hinge, which allows large-scale dynamic bending. Furthermore, partial unwinding-rewinding in the triple-helical coiled-coil structure of the proximal section permits gross fiber rotation and twisting. The two dynamic regions allow for large-scale, rapid fiber flexing and extension, thus enabling an efficient topological search for anchorage sites by the phage on the host surface. Since the fiber-assisted topological search is likely a universal mechanism of host recognition, modulating it could be used for fine-tuning the phage-bacterium infection process.