Fig. 4. Bending of the tail tube is mediated by flexible hinge regions.

a Model of a bent SPP1 tail tube with a curvature radius of 655 Å (as indicated by the arrow). The model is based on the structure of straight tubes and 2D class averages of bent tubes. Most structural changes are found on the outside of the curve (red) which implies that the bending process is mediated by stretching. b Regions that act as hinges during bending of the tube are colored in pink. c Variances in the cryo-EM map (pink) match the hinge regions. d Also, hinge regions are associated with highest ¹⁵N R₁ (color key) and R_1ρ (thickness of wire) relaxation rates. White coloring represents missing values. e Decaying relaxation dispersion profiles indicate the presence of slow motions. f Relaxation dispersion profiles of the inner β-barrel can be fitted in a correlated manner to a two-state exchange process. Smallest chemical shift changes correlate with middle regions of the β-barrel which are furthest away from the hinge regions (color key). The direction of the tail structure is baseplate upwards. Source data are provided as a Source Data file.