PARENT SESSION
Posters P5C Biosynthesis and assembly: Pigments. Abstracts (643-659)

PSII assembly in CP47 mutant of Synechocystis sp. PCC 6803 is dependent on the level of chlorophyll precursors regulated by ferrochelatase. Roman Sobotka^{*,1, 2}, Josef Komenda^{1, 2}, Martin Tichy^{1, 2}, ¹ Institute of Physical Biology, Nove Hrady, Czech Republic² Institute of Microbiology, Trebon, Czech Republic

ABSTRACT- Chlorophyll, heme and other tetrapyrroles that are indispensable for photosynthesis are produced by the tetrapyrrole biosynthetic pathway. Besides their function as pigments and cofactors, it appears that they can also serve as signalling molecules. Although their involvement in regulatory network is only starting to be understood, it is evident that changes in tetrapyrrole metabolism effects broad spectrum of seemingly unrelated processes in the cell. We have characterized in detail non-photosynthetic PSII mutant carrying mutation in the CP47 chlorophyll-binding protein and its autotrophic pseudorevertant. This psedorevertant has secondary mutation in ferrochelatase, enzyme catalyzing insertion of ferrous iron into protoporphyrin IX. Unexpectedly, activity of this enzyme was almost four times increased in the original CP47 mutant. This increase was correlated with ten-fold decrease in the level of protoporphyrin IX, last common intermediate of both chlorophyll and heme biosynthesis, and four-fold decrease of Mg-protoporphyrins IX, early precursors of chlorophyll. In the pseudorevertant, where ferrochelatase activity was decreased to 10% of wild type level due to point mutation, levels of these porphyrins significantly increased to or above wild type levels. Decrease of ferrochelatase activity in the psedorevertant resulted in normal accumulation of mutated CP47 and its assembly into functional PSII. The same effect was achieved when the CP47 mutant was treated by specific inhibitor of ferrochelatase. We suggest that the CP47 mutation prevents proper chlorophyll binding to the CP47 apoprotein and stabilization of the holoprotein against proteolysis. Inhibition or inactivation of ferrochelatase in this mutant will lead to higher chlorophyll supply restoring chlorophyll binding and PSII assembly.

KEY WORDS: ferrochelatase, CP47 chlorophyll binding protein, tetrapyrrole biosynthesis, photosystem II