Untersuchungen zur Integration des D1-Proteins in die Thylakoidmembran von Synechocystis sp. PCC 6803

Abstract

Investigating the D1 protein integration process into the thylakoid membrane within the cyanobacterium Synechocystis sp. PCC 6803 was the scope of this thesis. Based on previous results it can be concluded that the Oxa1/Alb3/YidC homologue SynOxa1p is involved in the membrane integration of D1 as well as in its assembly into PSII in Synechocystis.The results of this thesis can be summarized as follows: Using the Split-Ubiquitin System (1) a direct interaction of SynOxa1p with the full-lenght D1 could be demonstrated. (2) D1 protein areas interacting with SynOxa1p have been localized in the N-terminal fragment of D1. The first transmembrane helix and a fragment of the first luminal loop (aa 81-110) of D1 are interacting with SynOxa1p. (3) Slr1531p - whose homologue cpSRP54 is involved in the membrane integration of D1 in higher plants - has been identified as an interaction partner of SynOxa1p. In contrast, no interaction between Slr1531p and D1 could be demonstrated. (4) The interaction sites of SynOxa1p with D1 and with Slr1531 have been determined. SynOxa1p is interacting via the N-terminal transmembrane helices 1 to 3 exclusively with Slr1531p, whereas the C-terminal helices 4 and 5 of SynOxa1p are showing affinity towards N-terminal fragments of D1. By studies of Synechocystis-polysomes an association of SynOxa1p with polysomes could be demonstrated and interactions between SynOxa1p and nascent chains of D1 have been identified. For the first time a co-translational interaction of SynOxa1p with D1 could be proven. Hence, SynOxa1p is involved already co-translationally in the D1 integration. The light-sensitive mutant slr1471-gfp has been analyzed in this thesis in which a C-terminal GFP-fusion of SynOxa1p leads to an impaired membrane integration and assembly of D1 into PSII. The results give evidence that despite the GFP-fusion SynOxa1-GFP is able to associate with polysomes and to interact co-translationally with translation intermediates of D1.