Reflections on the function of IsiA, a cyanobacterial stress-inducible, Chl-binding protein

Abstract

The isiA gene encodes a protein that is similar to the Photosystem II chlorophyll-binding protein CP43, but lacks the entire large lumenal loop of over 100 amino acids. What is the function of this IsiA protein? Research on IsiA has traveled a long and interesting path since it was first discovered by its large accumulation during growth under iron-limited conditions. What appeared to be a simple on-off switch for isiA based on iron concentration has developed into a much richer and more intriguing set of possibilities that involve its expression and function. We provide an overview of isiA transcriptional regulation by many environmental factors and its proposed functions. We also describe the response to oxidative stress by cells that lack the IsiA protein. It is now clear that isiA expression can be de-repressed in the presence of normal iron levels and that the regulatory mechanisms can be linked to the inter-relationship between iron homeostasis and oxidative stress. The de facto transcriptional control of isiA expression has expanded to include regulation at both the transcriptional and post-transcriptional levels.

A Comprehensive Analysis of the Peroxiredoxin Reduction System in the Cyanobacterium Synechocystis sp. Strain PCC 6803 Reveals that All Five Peroxiredoxins Are Thioredoxin Dependent

“…6A and C). The expression of the isiA gene, which encodes an iron deficiency-related chlorophyll-binding protein (36), was monitored under the same conditions as a control, since expression of this gene is known to be induced by hydrogen peroxide (30,62). The isiA gene was found to respond with a pattern similar to that of trxQ, prxII, and prxQ1 (Fig.…”

The Dynamics of Photosynthesis

“…IsiA is a chl a binding protein similar to CP43, a core antenna protein of PSII. The IsiA that is synthesized during iron deprivation forms a ring, consisting of 18 IsiA polypeptides, surrounding the PSI cores (see 276). The original concept concerning changes in the photosynthetic apparatus upon Fe deprivation was that of a reduction in the number of PSI centers and that each center would associate with a larger, newly synthesized antenna (38,42).…”

The cyanobacterial homologue of the RNA chaperone Hfq is essential for motility of Synechocystis sp. PCC 6803

“…The Synechocystis sp. PCC 6803 antisense RNA IsrR proved to negatively control the expression of the accessory photosynthesis protein IsiA (iron-stress-induced protein A), which dramatically accumulates upon several environmental challenges including iron depletion (reviewed by Singh & Sherman, 2007).…”