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.
Highlights
De novo fatty acid biosynthesis is an essential metabolic step for microbial growth as it provides fatty acids for phospholipid biosynthesis, which is crucial for the integrity of the cell membrane
Previous work has demonstrated that the PII protein GlnB from A. thaliana, as well as bacterial GlnB proteins from Azospirillum brasilense and E. coli interact with biotin carboxyl carrier protein (BCCP) (Rodrigues et al, 2014)
The interaction of BCCP with GlnB could be confirmed for unicellular cyanobacteria, and for the first time, an implication of PII signaling on acetyl-CoA metabolism could be demonstrated
Summary
De novo fatty acid biosynthesis is an essential metabolic step for microbial growth as it provides fatty acids for phospholipid biosynthesis, which is crucial for the integrity of the cell membrane. The first and committed step in fatty acid biosynthesis is catalyzed by the enzyme acetyl-CoA carboxylase (ACC). The ACC enzyme complex consists of three functional units: i) the biotin carboxyl carrier protein (BCCP, accB) is covalently modified at a conserved lysine residue with biotin; ii) biotin carboxylase (BC, accC) carboxylates the biotin residue during the catalytic cycle in an ATP-dependent manner and iii) carboxyl transferase (CT, accA and accD) translocates the “activated” CO2 in the active site from biotin to acetyl-CoA forming malonyl-CoA, the substrate for fatty acid elongation (Cronan and Waldrop, 2002). The enzyme is feedback inhibited by acyl-ACP (Jiang and Cronan, 1994) and the catalytic activity of CT is decreased by its own transcript when acetyl-CoA levels are low.
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