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Figure 2
(a) Cartoon representations of the TtX183A (left) and TtX183B (right) domain structures. The haem cofactor is shown in stick form, coloured by atom type, with carbons shown in green or cyan. The cysteines that covalently link to the haem moiety are also shown as sticks together with the axial me­thio­nine and histidine that coordinate the central iron atom. The positions of cysteines that form disulfide bonds are also shown as sticks and are highlighted by arrows. (b) Representative electron-density maps for TtX183A (left, with green carbon atoms) and TtX183B (right, with cyan carbon atoms). The 2Fobs − Fcalc map for each structure is shown in blue contoured at 1σ, and the Fobs − Fcalc map shows positive density in green and negative density in red contoured at 4σ. (c) The superposition of TtX183A (yellow) and TtX183B (orange) with SoxA (PDB ID 4v2k) in which the catalytic domain has been coloured grey and the electron-transfer domain has been coloured blue. The superpositions demonstrate how the haem propionates may be buried within a larger protein to facilitate electron transfer to or from a catalytic site.

IUCrJ
Volume 11| Part 2| March 2024| Pages 260-274
ISSN: 2052-2525
https://doi.org/10.1107/S2052252524001386