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bioRxiv · 10.1101/2025.11.13.688228

The ABCs of Cyanobacterial Glycogen: In Vitro Modelling of Glycogen Synthesis and Functional Divergence of Glycogen Synthases in Synechocystis sp. PCC 6803

Lee, K.·Bekiari, D.·Doello, S.·Forchhammer, K.
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Abstract

Glycogen is the principal carbon reserve in Synechocystis sp. PCC 6803. We reconstituted its biosynthetic pathway in vitro--GlgC (Glucose-1-phosphate adenylyltransferase), two glycogen synthase isoenzymes (GlgA1, GlgA2) and the branching enzyme GlgB--to define how supply, polymerisation and branching set flux and product structure. GlgA2 shows higher specific activity and cooperates with GlgB-generated branched primers, whereas GlgA1 has higher substrate affinity and responds more to primer concentration. Product profiling links mechanism to architecture: GlgA1 produces more-branched glycogen, while GlgA2 yields longer, less-branched polymers, with GlgB biasing utilisation towards GlgA2. The complementary behaviours of GlgA1 and GlgA2 provide capacity for rapid accumulation versus steady-state maintenance and offer dynamic metabolic levers to tune glycogen content and architecture in cyanobacteria.

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Lee, K., Bekiari, D., Doello, S., Forchhammer, K.. 2025-11-13. The ABCs of Cyanobacterial Glycogen: In Vitro Modelling of Glycogen Synthesis and Functional Divergence of Glycogen Synthases in Synechocystis sp. PCC 6803. https://doi.org/10.1101/2025.11.13.688228

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