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

ABSTRACT 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.