One of the NAD kinases, sll1415, is required for the glucose metabolism of Synechocystis sp. PCC 6803

Abstract

Pyridine nucleotides (NAD(P)(H)) are electron carriers that are the driving forces in various metabolic pathways. Phosphorylation of NAD(H) to NADP(H) is performed by the enzyme NAD kinase (NADK). Synechocystis sp. PCC 6803 harbors two genes (sll1415 and slr0400) that encode proteins with NADK homology. When genetic mutants for sll1415 and slr0400 (D1415 and D0400, respectively) were cultured under photoheterotrophic growth conditions only the D1415 cells showed a growth defect. In wild-type cells, the sll1415 transcript accumulated after the cells were transferred to photoheterotrophic conditions. Furthermore, NAD (P)(H) measurements demonstrated that a dynamic metabolic conversion was implemented during the adaptation from photoautotrophic to photoheterotrophic conditions. Electron microscopy observation and biochemistry quantification demonstrated the accumulation of glycogen in the D1415 cells under photoheterotrophic conditions at 96 h. Quantitative real-time reverse transcription PCR (qRT-PCR) demonstrated the accumulation of mRNAs that encoded glycogen biosynthesis-related enzymes in photoheterotrophic D1415 cells. At 96 h, enzyme activity measurement in the photoheterotrophic D1415 cells demonstrated that the activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were decreased, but the activities of glucose dehydrogenase were increased. Furthermore, metabolomics analysis demonstrated that the D1415 cells showed increased glucose-6-phosphate and 6-phosphogluconate content at 96 h. Therefore, sll1415 has a significant function in the oxidative pentose phosphate (OPP) pathway for catabolism of glucose under photoheterotrophic conditions. Additionally, it is presumed that the slr0400 had a different role in glucose catabolism during growth. These results suggest that the two Synechocystis sp. PCC 6803 NADKs (Sll1415 and Slr0400) have distinct functions in photoheterotrophic cyanobacterial metabolism.

Physiological Significance of NAD Kinases in Cyanobacteria

“…On the other hands, there was no apparent difference between the pntAB -deficient mutant and WT under the mixotrophic condition (20 μE/m 2 /s). Interestingly, sll1415 -deficient mutant, one of the NADK -deficient mutants in Synechocystis , and pntAB -deficient mutant showed the similar phenotype under the day-night rhythm in the presence of glucose and the mixotrophic condition (20 μE/m 2 /s) (Ishikawa et al, 2016, 2019; Kamarainen et al, 2017). Therefore, pntAB may maintain the NADPH pool with sll1415 by unknown coordination system.…”

“…Those authors reported that a sll1415 null mutation affected the strain’s NADK activity and NADP(H) levels more severely than did a slr0400 null mutation. Furthermore, we reported that the sll1415 -deficient mutant showed a growth-impaired phenotype under growth conditions that would typically yield photomixotrophy (with 12-h light/12-h dark cycling), and under light-activated heterotrophic condition (LAHG) conditions (in which cells are maintained in darkness but exposed to light for 15 min every 24 h) (Ishikawa et al, 2019). Moreover, we showed that WT cells exhibited approximately 2.2- and 1.8-fold increases in the levels of NADP + and NADPH (respectively; compared to 0 h) at 96 h after transfer from autotrophic to photoheterotrophic conditions.…”

“…Furthermore, analysis of sll1415 and slr0400 mRNA levels in WT during the acclimation to photoheterotrophic conditions suggested dynamic changes in NADP + biosynthesis. Based on detailed molecular analysis, we showed that Sll1415 appears to have a specific role in the oxidative pentose phosphate pathway, sustaining cell growth under photoheterotrophic conditions (Ishikawa et al, 2019).…”

“…When the slr0400 mutant was grown under photoautotrophic conditions, the amount of glycogen was decreased compared to that in WT. Additionally, the levels of the agp transcript (encoding ADP-glucose pyrophosphorylase) decreased in Δ0400 grown under photoautotrophic conditions (Ishikawa et al, 2019). Furthermore, the metabolomic profile of Δ0400 was different from those of WT and Δ1415 when grown under photoheterotrophic conditions (Ishikawa et al, 2016; Ishikawa et al, 2019).…”

“…Additionally, the levels of the agp transcript (encoding ADP-glucose pyrophosphorylase) decreased in Δ0400 grown under photoautotrophic conditions (Ishikawa et al, 2019). Furthermore, the metabolomic profile of Δ0400 was different from those of WT and Δ1415 when grown under photoheterotrophic conditions (Ishikawa et al, 2016; Ishikawa et al, 2019). Notably, the intracellular levels of major metabolites (such as fructose-6-phosphate and 6-phosphogluconate) were decreased in Δ0400 (Ishikawa et al, 2016).…”