F-specific filamentous phages, elongated particles with
circular
single-stranded DNA encased in a symmetric protein capsid, undergo
an intermediate step, where thousands of homodimers of a non-structural
protein, gVp, bind to newly synthesized strands of DNA, preventing
further DNA replication and preparing the circular genome in an elongated
conformation for assembly of a new virion structure at the membrane.
While the structure of the free homodimer is known, the ssDNA-bound
conformation has yet to be determined. We report an atomic-resolution
structure of the gVp monomer bound to ssDNA of fd phage in the nucleoprotein
complex elucidated via magic-angle spinning solid-state NMR. The model
presents significant conformational changes with respect to the free
form. These modifications facilitate the binding mechanism and possibly
promote cooperative binding in the assembly of the gVp–ssDNA
complex.