Polyprenols Are Synthesized by a Plastidial cis-Prenyltransferase and Influence Photosynthetic Performance

Abstract

Plants accumulate a family of hydrophobic polymers known as polyprenols, yet how they are synthesized, where they reside in the cell, and what role they serve is largely unknown. Using Arabidopsis thaliana as a model, we present evidence for the involvement of a plastidial cis-prenyltransferase (AtCPT7) in polyprenol synthesis. Gene inactivation and RNAi-mediated knockdown of AtCPT7 eliminated leaf polyprenols, while its overexpression increased their content. Complementation tests in the polyprenol-deficient yeast Δrer2 mutant and enzyme assays with recombinant AtCPT7 confirmed that the enzyme synthesizes polyprenols of ;55 carbons in length using geranylgeranyl diphosphate (GGPP) and isopentenyl diphosphate as substrates. Immunodetection and in vivo localization of AtCPT7 fluorescent protein fusions showed that AtCPT7 resides in the stroma of mesophyll chloroplasts. The enzymatic products of AtCPT7 accumulate in thylakoid membranes, and in their absence, thylakoids adopt an increasingly "fluid membrane" state. Chlorophyll fluorescence measurements from the leaves of polyprenol-deficient plants revealed impaired photosystem II operating efficiency, and their thylakoids exhibited a decreased rate of electron transport. These results establish that (1) plastidial AtCPT7 extends the length of GGPP to ;55 carbons, which then accumulate in thylakoid membranes; and (2) these polyprenols influence photosynthetic performance through their modulation of thylakoid membrane dynamics.

Structural elucidation of the heterodimericcis-prenyltransferase NgBR/DHDDS complex reveals novel insights in regulation of protein glycosylation

“…Our crystallographic analysis of the core catalytic domain reveals a unique N-terminal structure within DHDDS that is absent in bacterial UPPS. The N-terminal segment consists of a random coil (residues 1-10) and a short -helix (0; residues [11][12][13][14][15][16][17][18][19][20][21]. The coil starts from the gap between 2 and 3.…”

Metabolomics profiling reveals new aspects of dolichol biosynthesis inPlasmodium falciparum

“…These lipids are present in all membrane systems 15,16 but their biological functions besides protein glycosylation in the ER remains largely unknown. Recently, cis-polyisoprenoids gained special attention due to several breakthroughs in the field including improvements in the analytical techniques for their analysis 17,18 , partial identification of their enzymatic machinery 19 , and the discovery of new biological functions beyond glycosylation 20,21 . Among some of these biological functions are the regulation of the membrane fluidity 21 , stimulation of spore wall formation in yeast 20 , and scavenging free radicals in cell membranes [22][23][24] .…”

“…Recently, cis-polyisoprenoids gained special attention due to several breakthroughs in the field including improvements in the analytical techniques for their analysis 17,18 , partial identification of their enzymatic machinery 19 , and the discovery of new biological functions beyond glycosylation 20,21 . Among some of these biological functions are the regulation of the membrane fluidity 21 , stimulation of spore wall formation in yeast 20 , and scavenging free radicals in cell membranes [22][23][24] . Interestingly, in cancer cells 25 and P. falciparum 26 , protein dolichylation occurs as a post-translational event, but functions of such derivatives and enzymes involved in this posttranslational protein lipid modification remain unknown.…”

“…This step is called elongation and in animals occurs in the endoplasmic reticulum (ER) where its downstream products dolichyl phosphates (Dol-Ps) serve as lipid oligosaccharide carrier for protein N-glycosylation, C-and O-mannosylation and glycosylphosphatidylinositol (GPI) synthesis (reviewed in 28 ). In other organisms, cis-polyisoprenoid synthesis also occurs in peroxisomes (rat 29 , yeast 30 ), lipid droplets (yeast 20,31 ) and chloroplasts (plants, cyanobacteria 21,32 ). The postulated final steps of cis-polyisoprenoid biosynthesis involve dephosphorylation of PDP to polyprenol followed by reduction of the a-isoprene unit by polyprenol reductase (PPRD), also called SRD5A3 or DFG10 in mammals and yeast, respectively ( Fig.…”

The Who, What, and Where of Plant Polyprenol Biosynthesis Point to Thylakoid Membranes and Photosynthetic Performance

“…) being essential in N-glycosylation, the functions of plastid-localized polyprenols are less clear (reviewed in Surmacz and Swiezewska, 2011). New work from Akhtar et al (2017) exploring the biosynthesis of polyprenols in plants indicates that they could be important in thylakoid membrane dynamics.…”