Figure 2.
Four-helix bundle backbone after backbone construction, top view (A); and introduction of loops, side view (B). The interhelical distances depend on the position of the helices with respect to the porphyrin macrocycle: helices on one side of the PZn unit (cis-porphyrin) are closer than helices on opposite sides (trans-porphyrin). That is, the cis-porphyrin distance CD in panel A is smaller than the trans-porphyrin distance DE.