Function of the IsiA pigment–protein complex in vivo

Schoffman, Hanan; Keren, Nir

doi:10.1007/s11120-019-00638-5

Cited by 20 publications

(19 citation statements)

References 75 publications

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“…1D). This increased 682 nm fluorescence can be attributed to the induction of the IsiA pigment‐protein complex, which is typically associated with iron deficiency in cyanobacteria (Bibby et al ., 2001; Boekema et al ., 2001; Schoffman and Keren, 2019). The blue shift in the red absorption peak of chlorophyll in whole cell absorption spectra of slr1908 KD is also consistent with the induction of IsiA (Fig.…”

Section: Resultsmentioning

confidence: 99%

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A unique porin meditates iron‐selective transport through cyanobacterial outer membranes

Qiu

Jiang

Lis

et al. 2020

Environmental Microbiology

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Summary Cyanobacteria are globally important primary producers and nitrogen fixers with high iron demands. Low ambient dissolved iron concentrations in many aquatic environments mean that these organisms must maintain sufficient and selective transport of iron into the cell. However, the nature of iron transport pathways through the cyanobacterial outer membrane remains obscure. Here we present multiple lines of experimental evidence that collectively support the existence of a novel class of substrate‐selective iron porin, Slr1908, in the outer membrane of the cyanobacterium Synechocystis sp. PCC 6803. Elemental composition analysis and short‐term iron uptake assays with mutants in Slr1908 reveal that this protein is primarily involved in inorganic iron uptake and contributes less to the accumulation of other metals. Homologues of Slr1908 are widely distributed in both freshwater and marine cyanobacteria, most notably in unicellular marine diazotrophs. Complementary experiments with a homologue of Slr1908 in Synechococcus sp. PCC 7002 restored the phenotype of Synechocystis knockdown mutants, showing that this siderophore producing species also possesses a porin with a similar function in Fe transport. The involvement of a substrate‐selective porins in iron uptake may allow cyanobacteria to tightly control iron flux into the cell, particularly in environments where iron concentrations fluctuate.

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Section: Resultsmentioning

confidence: 99%

“…It has been well established that PSI is one of largest iron sinks in cyanobacteria and is degraded during Fe limitation (Raven et al ., 1999; Ma et al ., 2017; Schoffman and Keren, 2019). In line with the response characteristic of iron limitation, slr1908 KD exhibited decreased PSI content under Fe‐replete conditions (Fig.…”

Section: Resultsmentioning

confidence: 99%

A unique porin meditates iron‐selective transport through cyanobacterial outer membranes

Qiu

Jiang

Lis

et al. 2020

Environmental Microbiology

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“…The exact function of IsiA in cyanobacteria has remained obscure. There are three prevalent hypotheses for IsiA functions: (1) store the majority of chlorophylls to compensate for the loss of photosystems 17,64 ; (2) serve as an accessory antenna for PSI to increase the light cross-section of PSI 6,7,12,14,33,65 ; (3) dissipate excess excitation energy for photoprotection 9,16,66 . Our spectroscopic results indicated that IsiA could function as an alternative light-harvesting antenna funnelling energy to PSI under stress conditions (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…PSI can also be surrounded by two IsiA rings, 18 IsiA monomers in the first ring and 25 in the second ring, forming a larger IsiA−PSI supercomplex 15 . Other proposed roles of IsiA are an energy dissipator for photoprotection 9,16 and Chl storage 17 . Additionally, cyanobacterial thylakoid membranes also accommodate components of the respiratory electron transport chains, comprising type-I NAD(P)H dehydrogenase (NDH-1), succinate dehydrogenase, and terminal oxidases 2,3 .…”

Section: Introductionmentioning

confidence: 99%

Structural variability, coordination and adaptation of a native photosynthetic machinery

et al. 2020

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Cyanobacterial thylakoid membranes represent the active sites for both photosynthetic and respiratory electron transport. We used high-resolution atomic force microscopy to visualise the native organisation and interactions of photosynthetic complexes within the thylakoid membranes from the model cyanobacterium Synechococcus elongatus PCC 7942. The thylakoid membranes are heterogeneous and assemble photosynthetic complexes into functional domains to enhance their coordination and regulation. Under high light, the chlorophyll-binding proteins IsiA are strongly expressed and associates with Photosystem I (PSI) forming highly variable IsiA−PSI supercomplexes to increase the absorption cross-section of PSI. There are also tight interactions of PSI with Photosystem II (PSII), cytochrome b 6 f, ATP synthase, and NAD(P)H dehydrogenase complexes. The organisational variability of these photosynthetic supercomplexes permits efficient linear and cyclic electron transport and bioenergetic regulation. Understanding the organisational landscape and environmental adaptation of cyanobacterial thylakoid membranes may help inform strategies for engineering efficient photosynthetic systems and photo-biofactories.

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“…Second, IsiA plays a significant role in dissipating excess light energy and thus acts as a cellular photoprotectant (12,(25)(26)(27)(28)42). Third, under stress conditions, IsiA acts as a Chl reservoir and becomes an immediate source of chlorophylls when such stress is relieved and new photosystem complexes are formed (43)(44)(45)(46). In any case, the IsiA-only pigment protein complex needs to have an energy dissipation system to avoid deleterious effects of overexcitation and harmful radical formation.…”

Section: Discussionmentioning

confidence: 99%

A Novel Mode of Photoprotection Mediated by a Cysteine Residue in the Chlorophyll Protein IsiA

Chen

Niedzwiedzki

Bandyopadhyay

et al. 2021

mBio

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Oxygenic photosynthetic organisms have evolved a multitude of mechanisms for protection against high-light stress. IsiA, a chlorophyll a-binding cyanobacterial protein, serves as an accessory antenna complex for photosystem I. Intriguingly, IsiA can also function as an independent pigment protein complex in the thylakoid membrane and facilitate the dissipation of excess energy, providing photoprotection. The molecular basis of the IsiA-mediated excitation quenching mechanism remains poorly understood. In this study, we demonstrate that IsiA uses a novel cysteine-mediated process to quench excitation energy. The single cysteine in IsiA in the cyanobacterium Synechocystis sp. strain PCC 6803 was converted to a valine. Ultrafast fluorescence spectroscopic analysis showed that this single change abolishes the excitation energy quenching ability of IsiA, thus providing direct evidence of the crucial role of this cysteine residue in energy dissipation from excited chlorophylls. Under stress conditions, the mutant cells exhibited enhanced light sensitivity, indicating that the cysteine-mediated quenching process is critically important for photoprotection. IMPORTANCE Cyanobacteria, oxygenic photosynthetic microbes, constantly experience varying light regimes. Light intensities higher than those that saturate the photosynthetic capacity of the organism often lead to redox damage to the photosynthetic apparatus and often cell death. To meet this challenge, cyanobacteria have developed a number of strategies to modulate light absorption and dissipation to ensure maximal photosynthetic productivity and minimal photodamage to cells under extreme light conditions. In this communication, we have determined the critical role of a novel cysteine-mediated mechanism for light energy dissipation in the chlorophyll protein IsiA.

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Function of the IsiA pigment–protein complex in vivo

Cited by 20 publications

References 75 publications

A unique porin meditates iron‐selective transport through cyanobacterial outer membranes

A unique porin meditates iron‐selective transport through cyanobacterial outer membranes

Structural variability, coordination and adaptation of a native photosynthetic machinery

A Novel Mode of Photoprotection Mediated by a Cysteine Residue in the Chlorophyll Protein IsiA

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