Interaction of the Nitrogen Regulatory Protein GlnB (PII) with Biotin Carboxyl Carrier Protein (BCCP) Controls Acetyl-CoA Levels in the Cyanobacterium Synechocystis sp. PCC 6803

Abstract

The family of PII signal transduction proteins (members GlnB, GlnK, NifI) plays key roles in various cellular processes related to nitrogen metabolism at different functional levels. Recent studies implied that PII proteins may also be involved in the regulation of fatty acid metabolism, since GlnB proteins from Proteobacteria and from Arabidopsis thaliana were shown to interact with biotin carboxyl carrier protein (BCCP) of acetyl-CoA carboxylase (ACC). In case of Escherichia coli ACCase, this interaction reduces the kcat of acetyl-CoA carboxylation, which should have a marked impact on the acetyl-CoA metabolism. In this study we show that the PII protein of a unicellular cyanobacterium inhibits the biosynthetic activity of E. coli ACC and also interacts with cyanobacterial BCCP in an ATP and 2-oxoglutarate dependent manner. In a PII mutant strain of Synechocystis strain PCC 6803, the lacking control leads to reduced acetyl-CoA levels, slightly increased levels of fatty acids and formation of lipid bodies as well as an altered fatty acid composition.

Transcriptional regulation of acetyl CoA and lipid synthesis by PII protein in Synechococcus PCC 7942

“…Enhanced production of lipid in the P II mutant strain seems to be the results of high production of acetyl CoA and enhanced activity of acetyl CoA carboxylase. Production of high amount of lipid in P II mutant of Synechococcus sp.PCC 7942 has already been reported . However, no detectable alteration in total carbohydrate content and a prominent reduction in the protein content of the P II mutant strain, as compared to the wild type, could also be a reason of enhanced lipid synthesis.…”

“…The reduction in acetyl CoA content, even after the surplus production of pyruvate dehydrogenase transcript, may be because of its rapid conversion to malonyl CoA due to the high activity of ACCase enzyme. P II deficiency induced curtailment of acetyl CoA content has recently been reported in Synechocystis PCC 6803 [19].…”

“…This regulation is mainly based on the protein–protein interaction and the interaction essentially requires the presence of 2‐oxogluterate and ATP. In Synechococcus PCC 7942, ACCase activity is also regulated by P II protein . In the present investigation, we examined the effects of P II deficiency on the transcript levels of genes essentially required for fatty acid synthesis in Synechococcus sp.…”

“…In Synechococcus PCC 7942, ACCase activity is also regulated by P II protein [19]. In the present investigation, we examined the effects of P II deficiency on the transcript levels of genes essentially required for fatty acid synthesis in Synechococcus sp.…”

The nitrogen regulator PipX acts in cis to prevent operon polarity

“…The PII trimer has three binding sites for ATP/ADP (in some species AMP) and 2-OG (Fokina et al, 2010;Palanca et al, 2014). PII binds to N-acetyl-Lglutamate kinase (NAGK), stimulating its activity and promoting nitrogen storage as arginine in cyanobacteria and plants (Burillo et al, 2004;Heinrich et al, 2004;Llacer et al, 2007), and to the biotin carboxyl carrier protein (BCCP) of acetyl-CoA carboxylase (ACCase), inhibiting its activity to control acetyl-CoA levels in organisms encoding PII (Feria Bourrellier et al, 2010;Gerhardt et al, 2015;Hauf et al, 2016). PII-dependent inhibition of nitrate transport is known to occur after addition of ammonium to nitrate-containing cultures (Lee et al, 1998), a function that, although poorly characterized at the molecular level, depends on the NrtC subunit of the nitrate transporter (NRT) (Kobayashi et al, 1997).…”