Abstract
Cyanobacteria are photosynthetic prokaryotes that perform oxygenic photosynthesis. Due to their ability to use the photon energy of sunlight to fix carbon dioxide into biomass, cyanobacteria are promising hosts for the sustainable production of terpenoids, also known as isoprenoids, a diverse class of natural products with potential as advanced biofuels and high-value chemicals. However, the cyanobacterial enzymes involved in the biosynthesis of the terpene precursors needed to make more complicated terpenoids are poorly characterized. Here we show that the predicted type II prenyltransferase CrtE encoded by the model cyanobacterium Synechococcus sp. PCC 7002 is homodimeric and able to synthesize C20-geranylgeranyl pyrophosphate (GGPP) from C5-isopentenyl pyrophosphate (IPP) and C5-dimethylallyl pyrophosphate (DMAPP). The crystal structure of CrtE solved to a resolution of 2.7 Å revealed a strong structural similarity to the large subunit of the heterodimeric geranylgeranyl pyrophosphate synthase 1 from Arabidopsis thaliana with each subunit containing 14 helices. Using mutagenesis, we confirmed that the fourth and fifth amino acids (Met-87 and Ser-88) before the first conserved aspartate-rich motif (FARM) play important roles in controlling chain elongation. While the WT enzyme specifically produced GGPP, variants M87F and S88Y could only generate C15-farnesyl pyrophosphate (FPP), indicating that residues with large side chains obstruct product elongation. In contrast, replacement of M87 with the smaller Ala residue allowed the formation of the longer C25-geranylfarnesyl pyrophosphate (GFPP) product. Overall, our results provide new structural and functional information on the cyanobacterial CrtE enzyme that could lead to the development of improved cyanobacterial platforms for terpenoid production.
Highlights
Cyanobacteria are a group of gram-negative photosynthetic prokaryotes that perform oxygenic photosynthesis using sunlight to drive the conversion of CO2 into a variety of carbon-based compounds
For Syn7002, three hypothesized prenyltransferases genes have been annotated in the genome sequence in UniProt: crtE (SYNPCC7002_A1085), sdsA (SYNPCC7002_A0580), and uppS (SYNPCC7002_A0099), which are considered to function as geranylgeranyl pyrophosphate synthase (GGPPS), solanesyl pyrophosphate synthase (SPPS) and undecaprenyl pyrophosphate synthase (UPPS) enzymes, respectively
We have demonstrated that the crystal structure of GGPPS (CrtE) enzyme encoded by the model cyanobacterium Syn7002 codes for a Type-II GGPPS
Summary
Cyanobacteria are a group of gram-negative photosynthetic prokaryotes that perform oxygenic photosynthesis using sunlight to drive the conversion of CO2 into a variety of carbon-based compounds. Cyanobacteria are widely considered as promising hosts for the sustainable production of biofuels and commodity and high-value chemicals. Crystal Structure of Cyanobacterial CrtE of secondary metabolites with over 70,000 compounds identified (Vickers et al, 2014) including carotenoids, sterols, steroids, saponins, and hormones, which are widely used in a range of applications, including pharmaceuticals, pesticides, fragrances, flavors, and advanced biofuels (Rabinovitch-Deere et al, 2013). All terpenoids are synthesized from two isomeric C5 building blocks: isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), both produced via the 2-C-methylD-erythritol-4-phosphate (MEP) pathway in cyanobacteria (Figure 1). A diverse range of polyprenyl pyrophosphate products (>C25) can be further synthesized through addition of different numbers of IPP to the FPP allylic substrate (Wallrapp et al, 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
