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Canino, Giusy (2006): Characterisation and functional analysis of a lumenal proline isomerase from photosynthetic membranes of higher plants and cyanobacteria. Dissertation, LMU München: Fakultät für Biologie



TLP40 is the first complex immunophilin which was described from plant chloroplasts (Fulgosi et al., 1998). For this protein a role in regulation of PSII protein phosphorylation has been suggested (Fulgosi et al., 1998; Vener et al., 1999; Rokka et al., 2000). Homologous proteins were found in Arabidopsis thaliana and in Synechocystis. In Synechocystis, different from higher plants, the relevant PSII proteins are not phosphorylated. The main topic of this work was therefore to characterise the homologous protein of TLP40 in Synechocystis (named cTLP40, cyanobacterial TLP40). The investigation shows: • cTLP40 contains the major structural domains of TLP40 both at the N- and at the C-termini. A higher homology is found in the immunophilin domain located at the C-terminal end. • As in chloroplasts, cTLP40 is also located in the thylakoid lumen where it is present in free form or associated to the membrane. • A Synechocystis strain lacking cTLP40 ( ∆sll0408) could grow photoautotrophycally under normal grown conditions in a way comparable to wild-type. However, after adaptation to strong light the mutant strain showed higher photosensibility. Under these conditions, there was a decrease in oxygen evolution. • The total amount of PSII dimer was reduced in the mutant under high light. The lower amount of PSII can be attributed to a slower assembly rate of the complex and/or to higher degradation rate. Protein synthesis was not impaired under any of the tested conditions. • The PPIAse activity of cTLP40 was tested in vitro on synthetic prolinecontaining peptides of PSII proteins which are exposed to the lumenal face in thylakoids. The in vitro assays showed that cTLP40 possesses PPIAse activity on control peptides but can not efficiently isomerise the specific synthetic peptides.