PBS linker protein ApcG binding site, conservation, and domain structure. A) Overview of Synechocystis PBS (left) and zoomed in view of ApcG binding site at the bottom cylinder (right). B) Primary structure of Synechocystis ApcG. Phosphorylation sites are highlighted in red, while PBS-binding region is in purple. C) Sequence conservation logo of 347 cyanobacterial ApcG homologs. The N-terminal conserved region is highlighted in yellow, positively charged region in blue, and C-terminal PBS-binding region in purple. The conserved FxxM motif is highlighted with a dashed box. D) AlphaFold predicted structure (colored according to prediction confidence) of residues 1 to 121 of ApcG (not present in the cryo-EM structure) of the combined model of the PBS interaction domain from the cryo-EM structure (purple). Phosphorylation sites are shown as red spheres.