Fig. 5: The muzzle assembly.
a, Top, two opposing subunits of the muzzle protein shown as ribbons (red). Bottom, a hexamer of the muzzle viewed along the central axis with cargo protein in purple. Circled numbers denote the blades of the β-propeller. b, A single subunit of the muzzle protein (right chain in a rotated by 90° around the central tunnel axis), with the ring-joining domain in orange, the β-propeller domain in green, the immunoglobulin-like domain 1 (IG1) in pink, IG2 in cyan and the crass domain polypeptide segments in light blue and yellow. c, Topology diagram of the muzzle protein with domains coloured as in b. The dotted line in the crass domain indicates the β-barrel strands. d, Schematic of the muzzle protein with individual domains coloured as in b,c, with domain boundary residue numbers indicated. β, β-propeller domain. R, ring-joining domain.
