PARENT SESSION
Plenary Lectures 3
Wednesday September 1st, 2004 8:30 AM Room 210A

Structure and function of Photosystem I and II. Petra Fromme^*,, HongQi Yu¹, Ingo Grotjohann¹, Yana Bukhman¹, Craig Jolley¹, Devendra Chauhan¹, Alexander Melkozernov¹, ¹ Department of Chemistry and Biochemsitry, Tempe, Arizona, USA

ABSTRACT- Photosystem I of cyanobacteria consists of 12 protein subunits, to which more than 100 cofactors are non-covalently bound: one functional unit of Photosystem I contains 96 Chlorophyll a molecules, 22 carotenoids, 3 Fe4S4-clusters and 2 phylloquinones that perform the complex function of light harvesting and charge separation. The X-ray structure of photosystem I at a resolution of 2.5 Angstrom [1] showed the location of the individual subunits and cofactors and provided new information on the protein-cofactor interactions. Recently, the structural model of plant PS I was determined by BenShem at al [2] shining ligth into the similarities and differences between the plant and cyanobacterial Photosystem I. In the talk, biochemical data and results of biophysical investigations are discussed with respect to the X-ray crystallographic structures of PS I in order to discuss the following open problems in Photosystem I: a) Interaction of Photosystem I with the soluble electron carriers b) Function of the antenna system in Photosystem I c) Interaction of Photosystem I with its peripheral antenna systems. Increasing knowledge on the structure and function of Photosystem II based in the crystals structures that had been determined from Photosystem II in the recent 3 years [3,4,5,6] resolution. The structures will be compared and discussed in respect to the function of Photosystem II with special focus on the oxygen-evolving complex. In the last part of the talk, the structures of Photosystem I and II will be compared and discussed in respect to the evolution of the Photosynthetic reaction centers. Special attention will be put on the discussion of how nature has shifted the redox potential of P680 to 1.1 V and how the oxygen evolving complex may have been evolved. [1] Jordan,P., Fromme,P.., Witt,H.T., O. Klukas , Saenger,W. and Krauss,N. (2001) Nature 411, 909-917 [2] Ben-Shem A, Frolow F, Nelson N (2003) Nature 426: 630-635 [3] Zouni A, Witt HT, Kern J, Fromme P, Krauss N, Saenger W, Orth P (2001) Nature 409: 739-743 [4] Kamiya N, Shen JR (2003) Proc Natl Acad Sci U S A 100: 98-103 [5] Fromme P, Kern J, Loll B, Biesiadka J, Saenger W, Witt HT, Krauss N, Zouni A (2002) Philos Trans R Soc Lond B Biol Sci 357: 1337-1344; discussion 1344-1335, 1367 [6] Ferreira KN, Iverson TM, Maghlaoui K, Barber J, Iwata S (2004) Science 303: 1831-1838

KEY WORDS: Photosystem II, Photosystem I, X-ray structure analysis, electron transfer