engleski

Membrane topology and dual localization of a protein switch directing photosynthetic electrons

At the end of the photosynthetic electron chain, at the stromal side of photosystem I, ferredoxin (Fd) hands over electrons to ferredoxin:NADPH oxydoreductase (FNR) or other stromal acceptors, depending on the organelle needs. This final electron transfer is regulated by the membrane-incorporated protein TROL (thylakoid rhodanase-like) that dynamically interacts with FNR and therefore influences the destination of photosynthetically-derived electrons. In the absence of TROL the distribution of high-energy electrons is directed towards the ROS detoxification pathways rather than to the NADP+ reduction. Trol plants show increased stress resistance along with significantly enhanced ROS detoxification. Also, the absence of TROL leads to the complete loss of the dynamicity of the FNR-binding and release to/from the thylakoid membranes. Recently, the topology of TROL has been investigated in order to define localization and orientations of its domains. TROL spans the thylakoid membranes by two segments, one at the N-terminus of the protein and the other close to its C-terminal part. C-terminal flexible PEPE domain and FNR-interacting ITEP domain protrude to the chloroplast stroma, while inactive, probably regulatory, RHO (rhodanase) domain resides in the thylakoid lumen. TROL is one of the few so far known dually localized chloroplast proteins. It is located in the inner envelope membrane of chloroplasts as a precursor of 70 kDa, and in the thylakoid membranes as 66 kDa mature form. Its role in the inner envelope has not been researched yet. By engineering the presequence processing site, a single amino acid exchange of Ala67 to Ile67 has been introduced to TROL, leading to inhibited processing and resulting protein incorporation at the single membrane location: in the inner envelope membrane. Constructing the Arabidopsis mutant plants, containing TROL protein just in the inner envelope, might further reveal its roles in regulation of photosynthesis and its yet unknown function in the envelope membrane.

Photosynthesis ; TROL ; FNR ; dinamicity ; dual localization ; topology

nije evidentirano