Fig. 3: Tail terminator and tail sheath proteins in native and contracted tail.

A Comparison of intermolecular contacts between tail terminator and tail sheath proteins in the phage 812 virion. A tail terminator protein is shown as an orange cartoon, an adjacent tail sheath protein in light green (domains III and IV were omitted) and a tail sheath protein from the second disc in dark green. Domain I segments of the tail sheath proteins highlighted in blue (α-helix residues 490–513), red (α-helix residues 522–538), and violet (β-turn residues 551–563) interact with the C-terminus of the adjacent tail sheath or tail terminator protein. B Comparison of contacts between tail terminator and tail sheath proteins after tail contraction. Domains III and IV of tail sheath proteins were omitted for clarity. The coloring of the proteins is identical to (A). The C-terminal β-strand of the tail terminator protein, and violet and red segments of domain I of the adjacent tail sheath protein, retain the same position as in the native structure. However, residues 490–513 (in blue), which in the native tail form an α-helix, reorganize. In contrast, the homologous interface between two adjacent tail sheath proteins retains the same structure as in the native tail, but its position is shifted. C Cryo-EM image of the neck/tail junction of the phage after tail contraction, showing the disordered state of domains III and IV of tail sheath proteins from the neck-adjacent disc (red arrows).