Directed mutagenesis indicates that the donor to P 680+ in photosystem II is tyrosine-161 of the D1 polypeptide

• Published in: Biochemistry (Easton) Vol. 27; no. 26; pp. 9071 - 9074
• Main Authors: Debus, R. J, Barry, B. A, Sithole, I, Babcock, Gerald T, McIntosh, L
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 27.12.1988
• Subjects: Chlorophyll - genetics; Chlorophyll - metabolism; Cyanobacteria - genetics; Cyanobacteria - metabolism; DNA Mutational Analysis; Free Radicals; Light-Harvesting Protein Complexes; Oxidation-Reduction; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex; Plant Proteins - genetics; Plant Proteins - metabolism; Tyrosine - metabolism
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00426a001

Photosystem II contains two redox-active tyrosines. One of these, YZ, reduces the reaction center chlorophyll, P680, and transfers the oxidizing equivalent to the oxygen-evolving complex. The second, YD, has a long-lived free radical state of unknown function. We recently established that YD is Tyr-160 of the D2 polypeptide by site-directed mutagenesis of a psbD gene in the unicellular cyanobacterium Synechocystis 6803 [Debus, R. J., Barry, B. A., Babcock, G. T., & McIntosh, L. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 427-430]. YZ is most likely the symmetry-related Tyr-161 of the D1 polypeptide. To test this hypothesis, we have changed Tyr-161 to phenylalanine by site-directed mutagenesis of a psbA gene in Synechocystis. The resulting mutant assembles PSII, as judged by its ability to produce the stable Y+D radical, but is unable to grow photosynthetically and exhibits altered fluorescence properties. The nature of the fluorescence change indicates that forward electron transfer to P+680 is disrupted in the mutant. These results provide strong support for our identification of Tyr-161 in the D1 polypeptide with YZ.