A novel periplasmic protein (Slr0280) tunes photomixotrophic growth of the cyanobacterium, Synechocystis sp. PCC 6803

• We report a slr0280-deleted mutant of Synechocystis, whose growth is moderately defective in the presence of glucose.
• Slr0280 is characterized as a novel periplasmic protein.
• DUF2233 domain of Slr0280 interacts with the several proteins that are relevant to carbohydrate metabolism.
• Slr0280 has a positive regulation on sugar catabolism and Calvin cycle.

Cyanobacteria are among the main contributors to global photosynthesis and show a high degree of metabolic plasticity. Synechocystis sp. PCC 6803 can grow under photoautotrophic, photomixotrophic or photoheterotrophic conditions. We have characterized a novel periplasmic protein (Slr0280) that tunes the photomixotrophic growth of Synechocystis sp. PCC 6803. Slr0280 is a multi-domain protein consisting mainly of β-sheets. Several proteins that interact with Slr0280 were identified via bacterial two-hybrid screening. Slr0280 may interact through its DUF2233 domain with partners that participate in sugar metabolism, thereby coordinating the respective regulations. When slr0280 was deleted, the mutant grew more slowly than wild-type in the presence of glucose, which is ascribed to the down-regulation of glycolysis, glycogen catabolism, oxidative pentose phosphate pathway, Calvin cycle and glucose utilization. A positive regulation of Slr0280 on these sugar catabolic enzymes was confirmed by transcript (qPCR) analyses. Based on these findings, we proposed a speculative model that Slr0280 plays a coordinating regulatory role in sugar metabolism.