Interplay of SpkG kinase and the Slr0151 protein in the phosphorylation of ferredoxin 5 in Synechocystis sp. strain PCC 6803.

In Synechocystis 6803, the ferredoxin 5 (Fd5) phosphoprotein and the S/T protein kinase SpkG are encoded by the slr0148 and slr0152 genes, respectively, which belong to the slr0144-slr0152 cluster. Using a targeted proteomic approach, we showed that SpkG is responsible for the phosphorylation of Fd5 on residues T18 and T72. Sequence alignments and Fd5 structure modelling suggest that these phosphorylation events modulate protein-protein interaction. Furthermore, Fd5 phosphorylation is affected by the Slr0151 protein encoded by the gene preceding spkG in the gene cluster. We propose that Slr0151 functions as an auxiliary protein in the regulation of the ratio between phosphorylated and nonphosphorylated forms of Fd5.