A giant chlorophyll–protein complex induced by iron deficiency in cyanobacteria

Abstract

Cyanobacteria are abundant throughout most of the world's water bodies and contribute significantly to global primary productivity through oxygenic photosynthesis. This reaction is catalysed by two membrane-bound protein complexes, photosystem I (PSI) and photosystem II (PSII), which both contain chlorophyll-binding subunits functioning as an internal antenna. In addition, phycobilisomes act as peripheral antenna systems, but no additional light-harvesting systems have been found under normal growth conditions. Iron deficiency, which is often the limiting factor for cyanobacterial growth in aquatic ecosystems, leads to the induction of additional proteins such as IsiA (ref. 3). Although IsiA has been implicated in chlorophyll storage, energy absorption and protection against excessive light, its precise molecular function and association to other proteins is unknown. Here we report the purification of a specific PSI-IsiA supercomplex, which is abundant under conditions of iron limitation. Electron microscopy shows that this supercomplex consists of trimeric PSI surrounded by a closed ring of 18 IsiA proteins binding around 180 chlorophyll molecules. We provide a structural characterization of an additional chlorophyll-containing, membrane-integral antenna in a cyanobacterial photosystem.

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“…Furthermore, a group of genes encoding polypeptides related to the early light-inducible proteins (ELIP) and LHCs of higher plants, the one-helix high-light-inducible proteins [HLIP, for reviews see Green and Durnford (1996); Montané and Kloppstech (2000)] has been found in cyanobacteria (Funk and Vermaas 1999). The results presented here, however, constitute the first evidence on protein level for membrane intrinsic light harvesting proteins in cyanobacteria besides the most recently found IsiA ring (Boekema et al 2001).…”

“…This would imply the necessity for one or more additional chlorophyll bearing polypeptides on which the superfluous Chl molecules could be organised. One attractive hypothesis would be that Gloeobacter contains additional membraneintegral light-harvesting proteins resembling the LHC proteins found in chloroplasts or the recently found CP43 (Riethman and Sherman 1988;Park et al 1999) or IsiA (Boekema et al 2001;Bibby et al 2001) in cyanobacteria. Such a hypothesis would support the assumption that Gloeobacter is the predecessor of chloroplasts.…”

“…Furthermore, chloroplast PS I is associated with membrane integral light-harvesting complexes (LHC I), which were so far assumed to be absent in cyanobacteria. Only recently, PS I from Synechococcus and Synechocystis has been shown to associate with a membrane intrinsic antenna when grown under iron limitation (Boekema et al 2001;Bibby et al 2001). Because of their sequence homology to CP43 these polypeptides had been originally attributed to PS II (Riethman and Sherman 1988;Park et al 1999).…”

Transmission Electron Microscopy as a Tool for the Characterization of Soft Materials: Application and Interpretation

“…It allows imaging of a large range of objects, from biological systems, e.g. cells7 or proteins,8, 9 to materials,10 aggregating of surfactants11, 12 and other self‐organising molecules into structures such as gels13 and vesicles 14. It is widely applied in both biology and organic and polymer chemistry.…”

Cross‐species Transcriptional Network Analysis Reveals Conservation and Variation in Response to Metal Stress in Cyanobacteria

“…At the same time, the up-regulation of "homologous recombination" might result in an increase of DNA mismatch repair and recombination [39]. Detailed analysis of genes with the same change trends (up-or downregulated) in both PMM and PMT under iron depletion condition suggested the mechanism that cyanobacteria employ to iron deficiency could be: firstly transporters were activated to obtain more iron from the environment [25], and photosynthesis and chlorophyll metabolism was inhibited due to the limited supply of iron [40][41][42], and then oxidative stress was enhanced and may cause RNA degradation, protein translation inhibition and other cellular metabolic changes. All these further resulted in inhibition of DNA replication and cell cycle block, and eventually growth cease.…”