Figure 6.

Helical wheels of EsxB and its alternative packing. (A) Helical wheel diagrams for the α1 and α2 helices of EsxB. The label α1N on the left side helix indicates the orientation of the α1 helix with its N-terminus pointing to the reader. The label α2C on the right side helix indicates the orientation of the α2 helix with its C-terminus pointing to the reader. (B) Packing of the AP dimer as observed in WT-EsxB and P67A mutant. Both α1 and α2 helices use their a and d positions for the helical bundle packing. One of two pairs of Q28-Y65 hydrogen bonds within the core of the dimer is highlighted. (C) Packing of the BU dimer as observed in WT-EsxB-His₆ and Y65F mutant. The α1 helix uses its a and e positions instead of a and d positions for helical packing. One of two Q28 residues and one of Y65 residues from the dimer were highlighted for their new positions in the WT-EsxB-His₆ BU dimer. In Y65F, Y65 is replaced by a phenylalanine.