Penn State Biology and Molecular Biology Home Page. Includes image map to PSU Home, BMB Home, and Eberly College of Science Home.

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

*Biological Substitution of Phylloquinone with Foreign Quinones*
We have approached this problem by constructing three different sets of mutations.
The only known function of phylloquinone (2-methyl-3-phytyl-1,4-naphthoquinone) in cyanobacteria and plants is to function as an electron transfer cofactor in Photosytem I. We determined that phylloquinone synthesis proceeds from from isochorismate and involves products of the menD, menC, menE, menB, ORF241, menA, and menG genes (Figure 2.1.4.). When menG is interrupted, demethylphylloquinone rather than plastoquinone-9 occupies the A1 site, and it functions as well as phylloquinone in forward electron transfer. However, when the menA, menB, menD or menE genes are interrupted, plastoquinone-9 occupies the A1 site and functions less well in forward electron transfer. What makes this so unusual is that phylloquinone in Photosystem I operates at a redox potential of ca. –800 mV, whereas plastoquinone-9 in Photosystem II operates at a midpoint potential of –150 mV. However, when plastoquinone-9 occupies the A1 site of Photosystem I, its redox potential becomes ca. –665 mV.
	Figure 2.1.4. Biosynthetic pathway of phylloquinone in Synechocystis sp. PCC 6803. The genes responsible for the biosynthesis of menaquinone were initially described in E. coli. Their homologs were identified in the genome of Synechocystis sp. PCC 6803 and the presence of menA, menB, menD, menE, and menG were confirmed by experiment.
Quite obviously, it is the protein environment of the quinone, and not the identity of the quinone, that is important for conferring the redox potential. Plastoquinone-9 is not the ideal quinone to occupy the A1 site, and as a consequence, it is easily displaced by substituted naphthoquinones, including those without long phytyl tails. This makes it possible to introduce isotopically-labeled quinones in the A1 site for spectroscopic study of structure/function relationships. What is remarkable is that the menG, menA, menB, menD and menE mutants are able to grow on light alone without supplementing their energy needs with a reduced carbon source.
References:
Johnson, T. W., Shen, G., Zybailov, B., Kolling, D., Reategui, R., Beauparlant, S., Vassiliev, I. R., Bryant, D. A., Jones, A. D., Golbeck, J. H., and Chitnis, P. R. (2000) Recruitment of a foreign quinone into the A1 site of photosystem I. I. Genetic and physiological characterization of phylloquinone biosynthetic pathway mutants in Synechocystis sp. PCC 6803, J Biol Chem, 275, 8523.Read PDF Zybailov, B., van der Est, A., Zech, S. G., Teutloff, C., Johnson, T. W., Shen, G., Bittl, R., Stehlik, D., Chitnis, P. R., and Golbeck, J. H. (2000) Recruitment of a foreign quinone into the A1 site of photosystem I. II. Structural and functional characterization of phylloquinone biosynthetic pathway mutants by electron paramagnetic resonance and electron-nuclear double resonance spectroscopy, J Biol Chem, 275, 8531.Read PDF Semenov, A. Y., Vassiliev, I. R., van der Est, A., Mamedov, M. D., Zybailov, B., Shen, G., Stehlik, D., Diner, B. A., Chitnis, P. R., and Golbeck, J. H. (2000) Recruitment of a foreign quinone into the A1 site of Photosystem I. Altered kinetics of electron transfer in phylloquinone biosynthetic pathway mutants studied by time-resolved optical, EPR and electrometric techniques, J Biol Chem, 275, 23429.Read PDF Johnson, T. W., Zybailov, B., Jones, A. D., Bittl, R., Zech, S., Stehlik, D., Golbeck, J. H., and Chitnis, P. R. (2001) Recruitment of a foreign quinone into the A1 site of Photosystem I. In vivo replacement of plastoquinone-9 by media-supplemented naphthoquinones in phylloquinone biosynthetic pathway mutants of Synechocystis sp. PCC 6803, J Biol Chem, 276, 39512.Read PDF Sakuragi, Y., Zybailov, B., Shen, G., Jones, A. D., Chitnis, P. R., van der Est, A., Bittl, R., Zech, S., Stehlik, D., Golbeck, J. H., and Bryant, D. A. (2002) Insertional inactivation of the menG gene, encoding 2-phytyl-1,4-naphthoquinone methyltransferase of Synechocystis sp. PCC 6803, results in the incorporation of 2-phytyl-1,4-naphthoquinone into the A1 site and alteration of the equilibrium constant between A1 and FX in Photosystem I, Biochem. 41, 394.Read PDF Johnson, T. W., and Golbeck, J. (2003) ‘Biological Incorporation of Alternative Quinones into Photosystem I’ in CRC Handbook of Organic Photochemistry and Photobiology (Lenci, F., Ed.), CRC Press, Boca Raton, FL.