The repair of photosystem II is a key mechanism that keeps the light reactions of oxygenic photosynthesis functional. During this process, the PSII central subunit D1 is replaced with a newly synthesized copy while the neighbouring CP43 antenna with adjacent small subunits (CP43 module) is transiently detached. When the D2 protein is also damaged, it is degraded together with D1 leaving both the CP43 module and the second PSII antenna module CP47 unassembled. In the cyanobacterium Synechocystis sp. PCC 6803, the released CP43 and CP47 modules have been recently suggested to form a so-called no reaction centre complex (NRC). However, the data supporting the presence of NRC can also be interpreted as a co-migration of CP43 and CP47 modules during electrophoresis and ultracentrifugation without forming a mutual complex. To address the existence of NRC, we analysed Synechocystis PSII mutants accumulating one or both unassembled antenna modules as well as Synechocystis wild-type cells stressed with high light. The obtained results were not compatible with the existence of a stable NRC since each unassembled module was present as a separate protein complex with a mutually similar electrophoretic mobility regardless of the presence of the second module. The non-existence of NRC was further supported by isolation of the His-tagged CP43 and CP47 modules from strains lacking either D1 or D2 and their migration patterns on native gels.

• Klíčová slova
• CP43, CP47, No reaction centre complex, Photosynthesis, Photosystem II,
• MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• fotosystém II (proteinový komplex) metabolismus   MeSH
• kyslík metabolismus   MeSH
• Synechocystis * genetika   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriální proteiny MeSH
• fotosystém II (proteinový komplex) MeSH
• kyslík MeSH

Photosystem II (PSII) is a large enzyme complex embedded in the thylakoid membrane of oxygenic phototrophs. The biogenesis of PSII requires the assembly of more than 30 subunits, with the assistance of a number of auxiliary proteins. In plants and cyanobacteria, the photosynthesis-affected mutant 68 (Pam68) is important for PSII assembly. However, its mechanisms of action remain unknown. Using a Synechocystis PCC 6803 strain expressing Flag-tagged Pam68, we purified a large protein complex containing ribosomes, SecY translocase, and the chlorophyll-binding PSII inner antenna CP47. Using 2D gel electrophoresis, we identified a pigmented Pam68-CP47 subcomplex and found Pam68 bound to ribosomes. Our results show that Pam68 binds to ribosomes even in the absence of CP47 translation. Furthermore, Pam68 associates with CP47 at an early phase of its biogenesis and promotes the synthesis of this chlorophyll-binding polypeptide until the attachment of the small PSII subunit PsbH. Deletion of both Pam68 and PsbH nearly abolishes the synthesis of CP47, which can be restored by enhancing chlorophyll biosynthesis. These results strongly suggest that ribosome-bound Pam68 stabilizes membrane segments of CP47 and facilitates the insertion of chlorophyll molecules into the translated CP47 polypeptide chain.

• MeSH
• 2D gelová elektroforéza MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• buněčná membrána metabolismus   MeSH
• chlorofyl metabolismus   MeSH
• fosfoproteiny genetika   metabolismus   MeSH
• fotosystém II (proteinový komplex) genetika   metabolismus   MeSH
• mutace MeSH
• ribozomy metabolismus   MeSH
• světlosběrné proteinové komplexy genetika   metabolismus   MeSH
• Synechocystis genetika   metabolismus   MeSH
• vazba proteinů MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• chlorofyl MeSH
• fosfoproteiny MeSH
• fotosystém II (proteinový komplex) MeSH
• photosystem II, chlorophyll-binding protein, CP-47 MeSH Prohlížeč
• photosystem II, psbH subunit MeSH Prohlížeč
• světlosběrné proteinové komplexy MeSH

We present proteomic, spectroscopic, and phylogenetic analysis of light-harvesting protein (Lhc) function in oleaginous Nannochloropsis oceanica (Eustigmatophyta, Stramenopila). N. oceanica utilizes Lhcs of multiple classes: Lhcr-type proteins (related to red algae LHCI), Lhcv (VCP) proteins (violaxanthin-containing Lhcs related to Lhcf/FCP proteins of diatoms), Lhcx proteins (related to Lhcx/LhcSR of diatoms and green algae), and Lhc proteins related to Red-CLH of Chromera velia. Altogether, 17 Lhc-type proteins of the 21 known from genomic data were found in our proteomic analyses. Besides Lhcr-type antennas, a RedCAP protein and a member of the Lhcx protein subfamily were found in association with Photosystem I. The free antenna fraction is formed by trimers of a mixture of Lhcs of varied origins (Lhcv, Lhcr, Lhcx, and relatives of Red-CLH). Despite possessing several proteins of the Red-CLH-type Lhc clade, N. oceanica is not capable of chromatic adaptation under the same conditions as the diatom Phaeodactylum tricornutum or C. velia. In addition, a naming scheme of Nannochloropsis Lhcs is proposed to facilitate further work.

• Klíčová slova
• Light harvesting, Thylakoid membrane, Vaucheriaxanthin, Violaxanthin–chlorophyll protein,
• MeSH
• fotosystém I (proteinový komplex) metabolismus   MeSH
• fylogeneze MeSH
• Heterokontophyta genetika   metabolismus   MeSH
• spektrofotometrie ultrafialová MeSH
• světlosběrné proteinové komplexy chemie   genetika   metabolismus   MeSH
• tandemová hmotnostní spektrometrie MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• fotosystém I (proteinový komplex) MeSH
• světlosběrné proteinové komplexy MeSH