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Figure 12
Final cryo-EM map of worm haemoglobin (scale bars indicate 50 Å). (a) Slice through the cryo-EM three-dimensional reconstruction perpendicular to the main sixfold symmetry axis, with the yellow arrow pointing at a haem group sandwiched between two α-helices; the proximal histidine contacting the iron in the haem group is visible. (b) Surface rendering of the top view (along the sixfold axis); the asymmetric unit (1/12th of the D6 reconstruction; see Supplementary Movie S1) is marked in yellow. (c) The asymmetric unit (`protomer' or `1/12th unit') with arrows pointing at the globin fold shown in (d) and the α-helix shown in (e). (d) View of one the better resolved haem groups: both the proximal and the distal histidine (b globin chain: His96 and His64) are well embedded in density. (e) View of one α-helix (L1 linker chain; Arg9–Leu38) in the triple coiled-coil region: the side chains fit nicely into the three-dimensional reconstruction. The atomic model was deposited as PDB entry 5m3l.

IUCrJ
Volume 4| Part 5| September 2017| Pages 678-694
ISSN: 2052-2525
https://doi.org/10.1107/S2052252517010922