engleski

TROL protein is necessary for efficient photosynthetic linear flow and energy supply to entire cell

In linear photosynthetic energy flow final electron transfer from ferredoxin to NADP+ is accomplished by a flavoenzyme ferredoxin:NADP+ oxidoreductase (FNR). Recently identified integral thylakoid membrane protein TROL (thylakoid rhodanase-like) docks FNR and ensures efficient linear electron transfer (Plant J 2009, 60: 783). TROL interacts with FNR via the C-terminal ITEP domain similar to the repeats found in Tic62 protein family. Yeast-two-hybrid analysis indicates very strong ITEP-FNR interaction which exceeds Tic62-FNR interaction by more than 8 fold. ITEP domain is attached to the rest of the protein through a proline-valine rich region (PVP hinge) which probably provides a flexible joint between ITEP and the membrane anchor. The region likely allows free movement of the tethered FNR. A centrally positioned rhodanese-like domain might be responsible for binding of plastoquinone (PQ). This interaction could link PQ redox state with the redox state of the stroma. Absence of TROL-FNR interaction causes decrease in linear electron transfer rate with concomitant increase in non-photochemical quenching, which leads to a distinctive high-light phenotype of Trol knock-out plants. Initial evidence points towards a dynamic, light-dependent, association of FNR with TROL. TROL-FNR complex is established in dark while in light FNR is being released. In the absence of TROL, plants suffer a severe deficiency in leaf pyridine nucleotide pool which indicates that interaction of FNR with thylakoid membranes exerts a more general impact on cellular energetics. Furthermore, lack of this interaction leads to changes in the redox poise of the entire cell, the NADP(H) pool is shifted towards more reduced state. We propose that TROL serves as an inducible switch for binding and release of FNR and maintenance of chloroplast and cellular redox poise.

ferredoxin-NADP+:oxidoreductase (FNR); TROL; linnear electron flow

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