The novel P <sub>II</sub> -interactor PirC identifies phosphoglycerate mutase as key control point of carbon storage metabolism in cyanobacteria
Tim Orthwein, Jörg Scholl, Philipp Spät, Stefan Lucius, Moritz Koch, Boris Maček, Martin Hagemann, Karl Forchhammer
Abstract
Significance In this work, we identified the regulatory mechanism of the key control point of cyanobacterial carbon metabolism, the glycolytic phosphoglycerate mutase (PGAM) reaction, converting 3-PGA into 2-PGA and thereby exporting organic carbon from the photosynthetic Calvin cycle. We show that PGAM activity is controlled by a small modulator protein PirC (product of sll0944 ), which inhibits the enzyme through protein–protein interaction. The availability of PirC for PGAM inhibition is controlled by the pervasive carbon/nitrogen balance regulator P II , which sequesters PirC at low 2-oxoglutarate levels and releases it at high 2-oxoglutarate levels. PirC-mediated inhibition of PGAM triggers glycogen accumulation, and disrupting this regulation allows the redirection of carbon flux, a decisive requirement for transforming cyanobacteria into green factories.