FabG can function as PhaB for poly-3-hydroxybutyrate biosynthesis in photosynthetic cyanobacteria Synechocystis sp. PCC 6803

Abstract

The production of poly-3-hydroxybutyrate (PHB) by photosynthetic cyanobacteria is a potentially sustainable production method for the biodegradable plastics industry. β-Ketoacyl-ACP reductase (FabG), from the photosynthetic cyanobacterium Synechocystis sp. PCC 6803 (SpFabG), is the first NADPH-dependent reductase in the fatty acid biosynthesis pathway. Its structure is similar to that of acetoacetyl-CoA reductase (SpPhaB), which is critical for PHB synthesis and can replace SpPhaB for acetoacetyl-CoA reduction in vitro. However, the specific function of SpFabG in fatty acid synthesis and whether SpFabG could participate in PHB synthesis in vivo were not yet clear. In this study, the role of SpFabG in fatty acid synthesis was first verified in vivo by knocking down and overexpressing of fabG. It was shown that SpFabG was essential yet not rate-limiting for fatty acid biosynthesis. The biochemical characterization of SpFabG using acetoacetyl-CoA as the substrate showed that the optimum temperature, optimum pH, K and k were 30°C, 7, 2.30 mM, and 19.85 s, respectively, which exemplified the ability of SpFabG to reduce acetoacetyl-CoA with a relatively low affinity and weak catalytic efficiency. Functional analysis of SpFabG in vivo indicated that SpFabG was able to partially complement SpPhaB under nitrogen-deprived conditions, and overexpression of fabG led to the diversion of partial carbon flux from fatty acid toward PHB synthesis.

Adaptation Strategies to High Hydrostatic Pressures in Pseudothermotoga species Revealed by Transcriptional Analyses

“…In addition, FabG often substitutes other dehydrogenases to produce secondary metabolites that may play a role in membrane permeability. It is also involved in polyhydroxyalkanoate (PHA) production, a form of carbon and energy storage under stress conditions [ 56 ]. In view of these putative functions, the differential expression of the fabG paralogs may explain the slight modification of the FA membrane composition in response to increasing hydrostatic pressure and/or the microscopy observations of the chain morphotype that was previously reported at the highest hydrostatic pressure [ 22 ].…”

Harnessing Algal Peroxisomes for Efficient Poly Hydroxybutyrate Production

“…The PHB analysis was performed by gas chromatography coupled to mass spectrometry (GC−MS) as we described previously. 59 The cells at the late logarithmic phase (day 5 after initial cultivation) were harvested, and the freeze-dried samples (20 mg) were esterified with 1 mL of H 2 SO 4 −methanol (1:4, v/v) and 1 mL of chloroform at 100 °C for 5 h during which the PHB was converted to methyl 3-hydrobutyrate. After the samples cooled down to room temperature, 0.5 mL of distilled water was added and mixed for 1 min.…”

Polyhydroxybutyrate: A Useful Product of Chlorotic Cyanobacteria

“…The fatty acid and PHA pathways are further interconnected by enzymes, which catalyze reactions in both pathways. For ex-ample, the enzyme FabG, which is actually part of the fatty acid biosynthesis, can also catalyze the same function as PhaB, but with lower catalytic efficiency [Zhang et al, 2017]. An overview of the most important pathways involved in the PHA metabolism is shown in Figure 3 (except the PHA depolymerization).…”