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J. Biol. Chem., Vol. 278, Issue 45, 44222-44229, November 7, 2003

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Specific Isotopic Labeling and Photooxidation-linked Structural Changes in the Manganese-stabilizing Subunit of Photosystem II^*

Roseann K. Sachs¶, Kelly M. Halverson||, and Bridgette A. Barry**

From the Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, St. Paul, Minnesota 55108 and the Department of Chemistry, Colorado College, Colorado Springs, Colorado 80903

Photosystem II (PSII) oxidizes water to molecular oxygen; the catalytic site is a cluster of four manganese ions. The catalytic site undergoes four sequential light-driven oxidation steps to form oxygen; these sequentially oxidized states are referred to as the S_n states, where n refers to the number of oxidizing equivalents stored. The extrinsic manganese stabilizing protein (MSP) of PSII influences the efficiency and stability of the manganese cluster, as well as the rates of the S state transitions. To understand how MSP influences photosynthetic water oxidation, we have employed isotope editing and difference Fourier transform infrared spectroscopy. MSP was expressed in Escherichia coli under conditions in which MSP aspartic and glutamic acid residues label at yields of 65 and 41%, respectively. Asparagine and glutamine were also labeled by this approach. GC/MS analysis was consistent with minimal scrambling of label into other amino acid residues and with no significant scrambling into the peptide bond. Selectively labeled MSP was then reconstituted to PSII, which had been stripped of native MSP. Difference Fourier transform infrared spectroscopy was used to probe the S₁Q_A to transition at 200 K, as well as the S₁Q_B to transition at 277 K. These experiments show that aspargine, glutamine, and glutamate residues in MSP are perturbed by photooxidation of manganese during the S₁ to S₂ transition.

Received for publication, July 3, 2003 , and in revised form, August 19, 2003.

^* This work was supported by National Science Foundation Grants MCB 99-73324 (to R. K. S.) and MCB 01-34968 (to B. A. B.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^¶ Permanent address: Dept. of Chemistry and Biochemistry, Messiah College, One College Ave., Grantham, PA 17027.

^|| Present address: Bacteriology Division, United States Army Medical Research Inst. of Infectious Diseases, 1425 Porter St., Ft. Detrick, MD 21702.

^** To whom correspondence should be addressed: School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332. E-mail: barry{at}cbs.umn.edu.

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