engleski

A novel multi-functional chloroplast protein: identification of a 40 kDa immunophilin-like protein located in the thylakod lumen

We describe the identification of the first immunophilin associated with the photosynthetic membrane of chloroplasts. This complex 40 kDa immunophilin, designated TLP40 (Thylakoid lumen PPIase), located in the lumen of the thylakoids, was found to play a dual role in photosynthesis involving both biogenesis and intraorganelle signalling. It originates in the single-copy nuclear gene, is made as a precursor of 49.2 kDa with a bipartite lumenal targeting transit peptide, and is characterized by structure including a cyclophiline-like C-terminal segment of 20 kDa, a predicted N-terminal leucine zipper and potential phosphatase-binding domain. It can exist in different oligomeric conformations and attach to the inner membrane surface. It is confined predominantly to the nonappressed thylakoid regions, the site of protein integration into the photosynthetic membrane. The isolated protein possesses peptidyl-prolyl cis-trans isomerase protein folding activity characteristic of immunophilins, but it not inhibited by cyclosporin A. TLP40 also exerts an effect on dephosphorylation of several key protein of photosystem II, probably as a continuitet of a transmembrane signal transduction chain.This first evidence for a direct role of immunophilins in a photoautotrophic process suggests that light-mediated protein phosphorylation in photosynthetic membranes and the role of the thylakoid lumen are substantionally more complex than anticipated.

cyclophilin; PPIase; protein folding; thylakoid lumen; thylakoid protein phosphatase

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