Biology subjects

Orthwein, T.

Publications and source records attributed to Orthwein, T..

3 recordsLinked to original sources

bioRxiv2026

Conversion of CO2 into valuable products: Engineering the PirC-PGAM switch in cyanobacteria to direct carbon flux into desired products

BackgroundIn response to rising CO2 emissions driving global warming, there is an urgent need for a transition toward a sustainable bioeconomy. Photo-biotechnological processes based on oxygenic photosynthesis hold high potential for achieving CO2 neutrality and in this regard, cyanobacteria have emerged as promising biocatalysts. Rational metabolic engineering of cyanobacteria depends on a thorough understanding of native regulatory mechanisms governing primary metabolism, which can limit metabolic flux through specific pathways and, consequently, the formation of target products. Recent insights have identified a key regulatory node at the 2,3-bisphosphogylcerate-independent phosphoglycerate mutase (PGAM) reaction, where the metabolic flux from newly fixed carbon is redirected from the Calvin-Benson-Bassham (CBB) cycle towards lower glycolysis. This metabolic valve is controlled by the small inhibitor protein PirC, whose binding to PGAM is determined by the central signal transduction protein PII. ResultsIn this study, we exploit the PirC-PGAM interaction as a novel target for regulatory metabolic engineering in the model cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis). Chassis strains with engineered control of PGAM, defined as PGAM-ON or PGAM-OFF states, were generated using two complementary approaches: tuning pgam gene expression and modulating PirC abundance to regulate PGAM activity. The effectiveness of this regulatory engineering strategy was demonstrated by redirecting carbon flux toward two representative, naturally occurring products: sucrose, produced via gluconeogenesis fueled by the Calvin-Benson-Bassham (CBB) cycle, and succinate, an intermediate of the tricarboxylic acid (TCA) cycle. Narrowing the PGAM valve resulted in a threefold increase in sucrose accumulation. In contrast, opening the PGAM valve by relieving PGAM inhibition through pirC deletion or separate pgam overexpression resulted in up to an 18-fold increase in succinate excretion. Furthermore, similar genetic configurations were applied to enhance production of a heterologous compound, isoprene, derived from pyruvate. ConclusionsThis study establishes the PGAM valve as a tunable control point for the rational re-direction of carbon flux in Synechocystis and highlights small regulatory proteins as powerful targets for metabolic engineering. Together, these findings provide proof of concept for an advanced level of molecular engineering in cyanobacteria and to fully harness their biocatalytic potential in future photosynthesis-driven biotechnological applications.

bioengineering↗

bioRxiv2024

Structural elements of cyanobacterial co-factor-independent phosphoglycerate mutase that mediate regulation by PirC

The 2,3-bisphosphoglycerate-independent phosphoglycerate mutase (iPGAM) has been identified as a crucial regulating key point in the carbon storage metabolism of cyanobacteria. Upon nitrogen starvation, the iPGAM is inhibited by the PII-interacting regulator PirC, released from its interaction partner PII due to elevated 2-oxoglutarate levels. In-silico analysis of 338 different iPGAMs revealed a deep-rooted distinctive evolution of iPGAMs in cyanobacteria. Remarkably, cyanobacterial iPGAMs possess a unique loop structure and an extended C-terminus. Our analysis suggests that iPGAM forms a complex with three individual PirC monomers. Complex affinity is affected by the unique loop and the C-terminal structural elements. A C-terminal truncated enzyme showed loss of control by PirC and two-fold increased enzymatic activity compared to the iPGAM-WT. By contrast, deleting the loop structure drastically reduced the activity of this variant. By replacing the WT iPGAM in Synechocystis with different iPGAM variants, in which these structural elements were deleted, it became apparent that deletion of the C-terminal element showed a similar overproduction of polyhydroxybutyrate as deletion of the iPGAM-regulator PirC. However, in contrast to the latter, these strains showed higher over-all biomass accumulation, making them a better chassis for a production strain for PHB or other valuable substances than the PirC-deficient mutant. These findings significantly contribute to our understanding of the metabolic pathways in cyanobacteria and open up new avenues for further research in this field, inspiring future investigations and discoveries. ImportanceThe primordial cyanobacteria were responsible for developing oxygenic photo-synthesis early in evolution. Through endosymbiosis, they further evolved into the chloroplasts found in the plant kingdom. Many metabolic pathways within chloroplasts originated from cyanobacteria. However, differences emerged during their long separate evolution, providing insights into the endosymbiotic process. In the metabolic pathways involving fixed CO2, the co-factor-independent phosphoglycerate mutase (iPGAM) plays a crucial role by directing the first CO2 fixation product, 3-phosphoglycerate, towards critical anabolic path-ways. Our findings reveal a distinct evolution of iPGAM within oxygenic photo-synthetic organisms. We have identified two specific segments in cyanobacterial iPGAMs that tightly control the cellular carbon/nitrogen state through a specific protein interactor (PiC). This understanding of iPGAM has allowed us to engineer cyanobacterial strains with altered carbon fluxes. Since cyanobacteria can directly convert CO2 into valuable products, our results demonstrate a novel approach for developing a chassis for biotechnical use.

microbiology↗

bioRxiv2020

The Novel PII-Interacting Regulator PirC (Sll0944) Identifies 3-Phosphoglycerate Mutase (PGAM) as Central Control Point of Carbon Storage Metabolism in Cyanobacteria

Nitrogen limitation imposes a major transition in the life-style of non-diazotrophic cyanobacteria, which is regulated via a complex interplay of regulatory factors, involving, the nitrogen-specific transcription factor NtcA and the pervasive signal processor PII. Immediately upon nitrogen-limitation, newly fixed carbon is re-directed towards glycogen synthesis. How the metabolic switch for distributing fixed carbon to either glycogen or cellular building blocks is operated was poorly understood. Here we identify from Synechocystis sp. PCC 6803 a novel PII interactor, PirC, (Sll0944) that controls 3-phosphoglycerate mutase (PGAM), the enzyme that deviates newly fixed CO2 towards lower glycolysis. PirC acts as competitive inhibitor of PGAM and this interaction is tuned by PII/2-oxoglutarate. High oxoglutarate release PirC from PII-complex to inhibit PGAM. Accordingly, PirC deficient mutant, as compared to the wild-type, shows strongly reduced glycogen levels upon nitrogen deprivation whereas polyhydroxybutyrate granules are over-accumulated. Metabolome analysis revealed an imbalance in 3-phosphoglycerate to pyruvate levels in the PirC mutant, conforming that PirC controls the carbon flux in cyanobacteria via mutually exclusive interaction with either PII or PGAM.

microbiology↗