Structural characterization of T7 tail machinery reveals a conserved tubular structure among other Podoviridae family members and suggests a common mechanism for DNA delivery

Bacteriophage tail complexes play an essential role in host recognition and DNA delivery during virus infection. These molecular machines are composed of a tubular structure surrounded by fibers, with a central channel that acts as a conduit for DNA ejection. The T7 tail complex is formed by four proteins: connector (gp8), gatekeeper (gp11), nozzle (gp12), and fibers (gp17). Previous biochemical and structural studies allowed definition of the stoichiometry and order of assembly of these proteins. Here we compared the tail complex from other Podoviridae phages that infect bacteria with Gram− type envelopes (K1E, P-SSP7, and ε15), and found strong similarities with the T7 nozzle; this was supported by sequence alignment and secondary structure prediction studies. These similarities were not observed in the new reconstruction of protein p9 presented here, which builds the hexameric nozzle of ϕ29, a virus that infects Gram+ bacteria. The results suggest that the Podoviridae nozzle has evolved to adapt to membrane composition of the infected host.