PARENT SESSION
Posters P8B Supermolecular organization of the photosynthetic apparatus. Abstracts (592-611)

Putative photosynthesome from Anacystis nidulans: A supermolecular organization of the photosynthetic apparatus. Diksha Dani^*,1, Jayashree Sainis¹, ¹ Molecular Biology Division, Mumbai, MS, India

ABSTRACT- A putative photosynthesome has been isolated from cell free extracts of A. nidulans. This thylakoid membrane fraction sedimenting at 150000 x g has all the components of electron transport chain, ATP synthase but no ferredoxin. Besides, it is associated with soluble proteins such as phycobilisomes, FNR and five sequential enzymes of Calvin cycle viz phosphoriboisomerase, phosphoribulokinase, Rubisco, 3-phosphoglycerate kinase and glyceraldehyde-3-phosphate dehydrogenase. This fraction was different in protein composition when compared with heavier thylakoid fraction sedimenting at 40000 x g. CP12, a non-enzymatic peptide required for oligomerization of phosphoribulokinase and glyceraldehyde-3-phosphate dehydrogenase was shown to be associated with thylakoid membranes. In vitro studies on the putative photosynthesome showed photophosphorylation and subsequent use of ATP for Calvin cycle, thus representing a functional photosynthetic module. Most of the components of photosynthesome remained associated even on sucrose density gradient centrifugation. Preincubation of cells in dark affected the functional efficiency of photosynthesome and decreased association of phycobilisomes with this module, indicating dynamic nature of the interactions. Preliminary experiments on de novo protein synthesis revealed highest rate of incorporation of labeled proteins in the photosynthesome on chlorophyll basis, when compared with the heavier fraction of thylakoid membranes. A supermolecular organization of the photosynthetic apparatus for synchronization of light and dark reactions is envisaged in the context of water-limited atmosphere in stroma where several soluble enzymes and pigment protein complexes have to function in consonance with each other. The new tools in proteomics and system biology will be useful in investigating the significance of modular organization for regulation of photosynthesis, thylakoid membrane biogenesis, assembly and repair.

KEY WORDS: Thylakoid membranes, Photosynthesis apparatus, Supermolecular organization, Calvin cycle