Light-sensitive phosphorylation regulates enzyme activity and filament assembly of human IMPDH1 retinal splice variants.

GTP biosynthesis. The vertebrate retina expresses two IMPDH1 splice variants that are critical for maintaining nucleotide levels required for phototransduction. Here, we show that filament assembly by these variants is itself controlled by phosphorylation at a single residue, adding further complexity to the tight regulation of nucleotide metabolism in the retina. Phosphorylation and other posttranslational modifications are likely to be a general regulatory mechanism controlling filament assembly by enzymes in many different metabolic pathways.