Isoprenoid biosynthesis in plant chloroplasts via the MEP pathway: Direct thylakoid/ferredoxin‐dependent photoreduction of GcpE/IspG

Abstract

In the methylerythritol phosphate pathway for isoprenoid biosynthesis, the GcpE/IspG enzyme catalyzes the conversion of 2-C-methyl-D D-erythritol 2,4-cyclodiphosphate into (E)-4-hydroxy-3-methylbut-2-enyl diphosphate. This reaction requires a double one-electron transfer involving a [4Fe-4S] cluster. A thylakoid preparation from spinach chloroplasts was capable in the presence of light to act as sole electron donor for the plant GcpE Arabidopsis thaliana in the absence of any pyridine nucleotide. This is in sharp contrast with the bacterial Escherichia coli GcpE, which requires flavodoxin/flavodoxin reductase and NADPH as reducing system and represents the first proof that the electron flow from photosynthesis can directly act in phototrophic organisms as reducer in the 2-C-methyl-D Derythritol 4-phosphate pathway, most probably via ferredoxin, in the absence of any reducing cofactor. In the dark, the plant GcpE catalysis requires in addition of ferredoxin NADP + /ferredoxin oxido-reductase and NADPH as electron shuttle.

Bisphosphonate Inhibitors Reveal a Large Elasticity of Plastidic Isoprenoid Synthesis Pathway in Isoprene-Emitting Hybrid Aspen

“…Furthermore, both HDS and HDR directly accept electrons from Fd in light (Eisenreich et al, 2001;Seemann et al, 2006;Li and Sharkey, 2013a). Thus, not only are the overall chloroplastic energetic and reductive levels decreased, but bisphosphonates likely also directly block the conversion of phosphorylated DXP/MEP pathway intermediates upstream of HMBDP, explaining a buildup of such huge pools in conditions in which DXP synthase runs faster than the reactions consuming the pathway end products (Fig.…”

“…However, there is evidence that diphosphate and its analogs are inhibitors of any ferredoxin (Fd)-dependent reaction (Forti and Meyer, 1969;Bojko and Wiȩckowski, 1999). This could be potentially relevant given that DXP/MEP pathwayreducing steps, at the level of 4-hydroxy-3-methyl-2-(E)-butenyl diphosphate (HMBDP) synthase (HDS) and reductase (HDR), directly accept electrons from Fd in light (Eisenreich et al, 2001;Seemann et al, 2006;Li and Sharkey, 2013a). In addition to the DXP/MEP pathway, inhibition at the level of Fd could also affect photosynthetic reactions and thereby alter energy supply for the DXP/MEP pathway.…”

Bioenergetics of Monoterpenoid Essential Oil Biosynthesis in Nonphotosynthetic Glandular Trichomes

“…4). The electron transfer reactions of reductive steps of the MEP pathway, catalyzed by 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate synthase (HDS) and 1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate reductase (HDR), employ Fd and FNR (Seemann et al, 2006;Rekittke et al, 2013). This cofactor requirement is in accordance with our modeling prediction that Fd recycling is essential for monoterpene biosynthesis (Table I).…”

Consequences of C4 Differentiation for Chloroplast Membrane Proteomes in Maize Mesophyll and Bundle Sheath Cells

“…Finally a number of stromal metabolic enzymes may functionally interact with the thylakoid, e.g. to transfer reducing equivalents to metabolic pathways, such as GcpE/IspG in the methylerythritol phosphate pathways (31). Thus, it is highly likely that numerous thylakoid (-associated) proteins with non-photosynthetic functions accumulate to different levels in the two cell types and may contribute to BS/M chloroplast differentiation; their quantification will help to better understand cell specific differentiation.…”