An AbrB‐like protein might be involved in the regulation of cylindrospermopsin production by Aphanizomenon ovalisporum

Abstract

Certain filamentous cyanobacteria, including Aphanizomenon ovalisporum, are potentially toxic owing to the formation of the hepatotoxin cylindrospermopsin. We previously identified a gene cluster in A. ovalisporum likely to be involved in cylindrospermopsin biosynthesis, including amidinotransferase (aoaA) and polyketide-synthase (aoaC), transcribed on the reverse strands. Analysis of the genomic region between aoaA and aoaC identified two transcription start points for each of these genes, differentially expressed under nitrogen and light stress conditions. The transcript abundances of these genes and the cylindrospermopsin level were both affected by nitrogen availability and light intensity. Gel shift assays and DNA affinity columns isolated a protein that specifically binds to a 150 bp DNA fragment from the region between aoaA and aoaC, and MS/MS analyses identified similarity to AbrB in other cyanobacteria and in Bacillus sp. Comparison of the native AbrB isolated from A. ovalisporum with that obtained after cloning and overexpression of abrB in Escherichia coli identified specific post-translational modifications in the native cyanobacterial protein. These modifications, which are missing in the protein expressed in E. coli, include N-acetylation and methylation of specific residues. We discuss the possible role of these modifications in the regulation of cylindrospermopsin production in Aphanizomenon.

Novel Insights into the Regulation of LexA in the Cyanobacterium Synechocystis sp. Strain PCC 6803

“…(40). It was suggested by the authors of that work that the posttranslational modifications may affect the structural organization of the protein and thus its affinity for DNA (40). In this work, we also provide evidence of differences between the LexA protein isolated from Synechocystis sp.…”

“…The identities of some of the peptides are given on the right. (40). It was suggested by the authors of that work that the posttranslational modifications may affect the structural organization of the protein and thus its affinity for DNA (40).…”

“…Instead, we identified different isoelectric forms of the protein. Other cyanobacterial transcription factors and signaling proteins have been shown to be modified after translation, as well, such as PII (phosphorylation) (10), the KaiC protein (phosphorylation) (49), and the AbrB-like protein in Aphanizomenon ovalisporum (N-acetylation and methylation) (40). Particularly in the last example, Shalev-Malul and coworkers identified differences between the native AbrB-like protein isolated from the cyanobacterium and the recombinant protein FIG.…”

CalA, a cyAbrB protein, binds to the upstream region of ftsZ and is down-regulated in heterocysts in Anabaena sp. PCC 7120

“…The identification of the cyAbrBs was all based on the use of DNA-binding chromatography. Similarly, a cyAbrB that may regulate the production of cylindrospermopsin has been identified in Aphanizomenon ovalisporum (Shalev-Malul et al 2008). Agervald et al (2010) showed that CalA can bind to the regulatory regions of hypC and alr0946(calA)-alr0947.…”

Proteomic analysis of post translational modifications in cyanobacteria

“…In cyanobacteria, only a few protein N-terminal acetylation events have been reported, for example, N-terminal acetylation of several proteins such as the Rieske iron-sulfur protein (PetC), Cytochrome b559 subunit beta (psbF) and Photosystem II reaction center protein J (psbJ) [39,74]. N-terminal acetylation of some cyanobacterial peptides [75] or toxins were also reported [76,77].…”