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John Golbeck

Professor of Biochemistry and Biophysics
Professor of Chemistry

310 South Frear Laboratory, University Park, PA 16802
Phone: (814) 865-1163
Fax: (814) 863-7024
E-mail: jhg5@psu.edu

B.S. in Chemistry from Valparaiso University
Ph.D. in Chemistry from Indiana University

Golbeck Lab Web Site

*Involvement of rubA in the Assembly of the FX Iron-Sulfur Cluster* (collaboration with Don Bryant)
Rubredoxins are typically very small (6 kDa), water-soluble, mononuclear non-heme iron proteins that occur most frequently in anaerobic eubacteria and archaea, but they are also found in a few aerobic bacteria, and more recently they have been identified in photosynthetic prokaryotes and eukaryotes. Synechocystis sp. PCC 6803 contains a single gene for a rubredoxin (rubA), which encodes a protein that contains a hydrophobic C-terminal domain that may serve to anchor it in the thylakoid membrane.We found that the FX cluster fails to assemble when the rubA gene is interrupted. Any proposed role for rubredoxin must therefore be consistent with the following. 1) The assembly of FX requires the presence of the rubA gene product; 2) The assembly of FX occurs at the last stage of PS I biogenesis, when charge separation is fully functional between P700 and A1; 3) The assembly of a [4Fe-4S] cluster is a highly coordinated process due to the toxicity of Fe2+ and S2-, and requires the participation of multiple gene products from either the isc or suf operons;
	Figure 2.2.3. Proposed role for the membrane-bound rubredoxin in the assembly of the FX iron-sulfur cluster. The protein is modeled based on known structures for soluble rubredoxin. The rubredoxin is proposed to accept electrons from A1 so as to allow the correct redox environment to exist as the Fe/S cluster is assembled into the FX site
4) The assembly of a [4Fe-4S] cluster involves highly controlled redox chemistry which ultimately results in two Fe2+ and two Fe3+ atom in the assembled cluster. Taking these considerations into account, it is clear that FX represents a special case because the assembly and insertion of the [4Fe-4S] cluster occurs within 10 to 12 Å of the electron acceptor A1-, one of the strongest reductants in biology (Em’ < –800 mV vs H2). We propose that the role of RubA is to provide a substitute electron acceptor from A1- during development so that a favorable redox environment exists for the assembly of the [4Fe-4S] cluster in the FX site (Figure 2.2.3.).
References:
Shen, G., Zhao, J., Reimer, S. K., Antonkine, M. L., Cai, Q., Weiland, S. M., Golbeck, J. H., and Bryant, D. A. (2002) Assembly of Photosystem I. I. Inactivation of the rubA gene encoding a membrane-associated rubredoxin in the cyanobacterium Synechococcus sp. PCC 7002 causes a loss of Photosystem I activity, J Biol Chem 277, 20343-54. Read PDF Shen, G., Antonkine, M. L., van der Est, A., Vassiliev, I. R., Brettel, K., Bittl, R., Zech, S. G., Zhao, J., Stehlik, D., Bryant, D. A., and Golbeck, J. H. (2002) Assembly of Photosystem I. II. Rubredoxin is required for the in vivo assembly of FX in Synechococcus sp. PCC 7002 as shown by optical and EPR spectroscopy, J Biol Chem 277, 20355-66. Read PDF