Recombinant Geobacter sulfurreducens 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase (ispD)

Introduction to Recombinant Geobacter sulfurreducens 2-C-Methyl-D-Erythritol 4-Phosphate Cytidylyltransferase (IspD)

Geobacter sulfurreducens is a bacterium known for its ability to transfer electrons extracellularly, making it useful in bioremediation and microbial fuel cells . Recombinant Geobacter sulfurreducens 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase (IspD) is an enzyme that plays a crucial role in the MEP (methylerythritol phosphate) pathway, which is essential for isoprenoid biosynthesis in bacteria and plants . Specifically, IspD catalyzes the reaction between 2-C-methyl-D-erythritol 4-phosphate (MEP) and CTP (cytidine triphosphate) to form 4-(cytidine 5'-diphospho)-2-C-methyl-D-erythritol (CDP-ME) .

Function and Importance of IspD

IspD is essential for synthesizing isoprenoids, which are involved in various cellular functions, including synthesizing quinones, sterols, and carotenoids . The MEP pathway, in which IspD functions, is vital for bacteria and plants because it is the sole route for isoprenoid biosynthesis in most bacteria and plants, but not in humans, making it a target for developing new antibacterial agents .

Role in Metabolic Engineering

Metabolic engineering of Geobacter sulfurreducens has shown that manipulating ATP demand can increase respiration rates by affecting the TCA cycle and NADPH oxidation . Overexpressing certain proteins, such as the hydrolytic portion of the ATP synthase complex, can create an ATP drain, leading to increased respiration rates and altered gene expression . These changes include increased expression of genes involved in energy metabolism and decreased expression of genes for amino acid biosynthesis and cell growth .

IspD in Geobacter sulfurreducens

IspD is present in organisms that also have dxs and dxr genes, which are part of the MEP pathway . The enzyme catalyzes the formation of 4-diphosphocytidyl-2C-methyl-D-erythritol from 2C-methyl-D-erythritol 4-phosphate and CTP .

Research Findings and Applications

• Increased Respiration Rates: Genetic engineering can increase respiration rates in G. sulfurreducens by increasing cellular ATP demand . This leads to higher fluxes through the TCA cycle and alters the expression of genes involved in energy metabolism and biosynthesis .

• Global Transcriptional Analysis: Studies on G. sulfurreducens have identified transcriptional regulators, such as GSU1771, that control extracellular electron transfer and exopolysaccharide synthesis, which are crucial for bioelectricity generation and bioremediation .

• Secondary Metabolites Discovery: Fungal co-culture strategies have been used to discover new secondary metabolites with various biological activities, such as α-glucosidase inhibition and antimicrobial properties .