Structure comparison between oxidized and reduced plastocyanin from a fern, Dryopteris crassirhizoma.

The X-ray crystal structures of oxidized and reduced plastocyanin obtained from the fern Dryopteris crassirhizoma have been determined at 1.7 and 1.8 A resolution, respectively. The fern plastocyanin is unique in the longer main chain composed of 102 amino acid residues and in the unusual pH dependence due to the pi-pi stacking interaction around the copper site [Kohzuma, T., et al. (1999) J. Biol. Chem. 274, 11817-11823]. Here we report the structural comparison between the fern plastocyanin and other plastocyanins from cyanobacteria, green algae, and other higher plants, together with the structural changes of fern plastocyanin upon reduction. Glu59 hydrogen bonds to the OH of Tyr83, which is thought to be a possible conduit for electrons, in the oxidized state. However, it moves away from Tyr83 upon reduction like poplar plastocyanin.