title: Importance of the cyanobacterial Gun4 protein for chlorophyll metabolism and assembly of photosynthetic complexes.
abstract: Gun4 is a porphyrin-binding protein that activates magnesium chelatase, a multimeric enzyme catalyzing the first committed step in chlorophyll biosynthesis. In plants, GUN4 has been implicated in plastid-to-nucleus retrograde signaling processes that coordinate both photosystem II and photosystem I nuclear gene expression with chloroplast function. In this work we present the functional analysis of Gun4 from the cyanobacterium Synechocystis sp. PCC 6803. Affinity co-purification of the FLAG-tagged Gun4 with the ChlH subunit of the magnesium chelatase confirmed the association of Gun4 with the enzyme in cyanobacteria. Inactivation of the gun4 gene abolished photoautotrophic growth of the resulting gun4 mutant strain that exhibited a decreased activity of magnesium chelatase. Consequently, the cellular content of chlorophyll-binding proteins was highly inadequate, especially that of proteins of photosystem II. Immunoblot analyses, blue native polyacrylamide gel electrophoresis, and radiolabeling of the membrane protein complexes suggested that the availability of the photosystem II antenna protein CP47 is a limiting factor for the photosystem II assembly in the gun4 mutant.
authors.affiliation: Institute of Physical Biology, University of South Bohemia, 37333 Nove Hrady, Czech Republic.
authors.forename: Roman
authors.initials: R
authors.lastname: Sobotka
authors.forename: Ulf
authors.initials: U
authors.lastname: Dühring
authors.forename: Josef
authors.initials: J
authors.lastname: Komenda
authors.forename: Enrico
authors.initials: E
authors.lastname: Peter
authors.forename: Zdenko
authors.initials: Z
authors.lastname: Gardian
authors.forename: Martin
authors.initials: M
authors.lastname: Tichy
authors.forename: Bernhard
authors.initials: B
authors.lastname: Grimm
authors.forename: Annegret
authors.initials: A
authors.lastname: Wilde
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008190:Lyases / Q000737:chemistry; D008854:Microscopy, Electron; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D010641:Phenotype; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D011166:Porphyrins / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D011166:Porphyrins; C070970:photosystem II, chlorophyll-binding protein, CP-47; D002734:Chlorophyll; D008190:Lyases; C086788:magnesium chelatase