Figure 4. Turn of W377 upon electron transfer.

Shown is a rearrangement of the W377 residue in Arabidopsis thaliana cryptochrome, namely a turn of the side group that is coupled to W377 → W400^·+ electron transfer. The turn comes about in the quantum chemical geometry optimization calculations depicted in Fig. 3 and involves also the positive W400^·+ radical and the polar environment of the W377 residue made up of residues Q401, T404, and T406. A T404^OG1 …W377^HE1 hydrogen bond (right panel, magenta) is formed upon the turn of W377.