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Figure 6
(a) Field of view of ice-embedded ΦCD508 particles showing how some tails have spontaneously contracted to eject part of the inner tube. In some contracted particles the capsid appears empty, whereas in others it appears to still contain DNA. Scale bar: ∼650 Å. (b) Comparison of surface models of urea-contracted ΦCD508 tail sheath (PDB ID 9gb6, mauve; Wilson et al., 2025View full citation) and spontaneously contracted sheath (green), showing three layers. The structures were aligned on one subunit in the lower of the three layers. (c) Superposition of sheath subunit from reprocessed urea contracted tail (grey) and naturally contracted tail (pale green). The bulk of the three domains behave as a rigid body but flexibility in the N-terminus is indicated by the arrow. (d) Comparison of three neighbouring sheath subunits from urea-contracted ΦCD508 tail (grey) with the equivalent subunits from the naturally contracted tail (coloured). Polypeptide chains have been aligned on the β-handshake domain where three chains meet around the C-terminus of the pale blue subunit and the N-terminus of the straw subunit (arrow). (e) Detail from (d) showing the region around the aligned β-handshake domain (arrow). The N-terminal linker (NTL) is partially unfolded in the urea-contracted tail (grey). This accommodates a shift in the X-loop (X) and thus a rigid-body movement of the subunit as a whole.

IUCrJ
Volume 13| Part 4| July 2026|
ISSN: 2052-2525
https://doi.org/10.1107/S2052252526005105