FIGURE 1. The C backbone trace, hydrophobic core distribution and structural information of F41.

a, Stereo diagram of the C backbone. The chain is colour coded from blue to red from the N to the C terminus. Prepared with MOLSCRIPT⁴⁴ and RASTER3D⁴⁵. b, Four distinct hydrophobic cores that define domains D1, D2a, D2b and D3. All the hydrophobic side-chain atoms are displayed with the C backbone. Side-chain atoms are colour coded: Ala, yellow; Leu, Ile or Val, orange; Phe and Tyr, purple (carbon atoms) and red (oxygen atoms). Prepared with RASMOL⁴⁶. c, Position and region of various structural features in the amino-acid sequence of flagellin. Shown are, from top to bottom: the F41 fragment in blue; three -folium folds in brown; the secondary structure distribution with -helix in yellow, -structure in green, and -turn in purple; tic mark at every 50th residue in blue; domains D0, D1, D2 and D3; the axial subunit contact region within the protofilament in cyan; the well-conserved amino-acid sequence in red and variable region in violet; point mutations in F41 that produce the filaments of different supercoils. Letters at the bottom indicate the morphology of mutant filaments: L (D107E, R124A, R124S, G426A), L-type straight; R (A449V), R-type straight; C (D313Y, A414V, A427V, N433D), curly³³.