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Figure 4
Crystal-packing implications for pilus assembly. (a) Crystal packing, showing pilus-like end-to-end stacking, with chain A shown in dark shades and chain B in light shades. The unit cell is indicated by a black box and a single asymmetric unit is shown in green. (b) A single pilus-like chain of molecules with domains coloured as per Fig. 1[link]. Directionality is indicated along with the order of incorporation of pilin subunits. (c) Close-up of the interface between monomers. The C-terminal residue of the preceding monomer (Gln453, the last visible residue of molecule B in the crystal) is shown in orange, located at the entrance to the D1 groove, and would be followed in full-length SpaD by eight more residues, of which the last four belong to the LPMTG sortase-recognition motif. These missing residues and their predicted path are indicated. The intermolecular isopeptide bond-forming lysine is located at the base of this groove, in position to bond to the Thr of the sortase motif, and is coloured green. The β1–β2 loop (magenta) forms one side of this groove and covers the lysine residue. (d) Overlay of SpaD chain A (blue) and chain B (red) and SpaA (green) aligned based on D2 and D3 showing the varying orientations of D1. Domains D2 and D3 are shown as a light grey surface with D1 and the first strand of D2 as a smoothed cartoon. Arrows indicate the relative orientation of each D1, with the rotation angle of each domain around the hinge region (N-terminus of the first strand of D2) calculated by DynDom (Hayward & Berendsen, 1998BB12).

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ISSN: 2059-7983
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