Functional Characterization of Lycopene Cyclases Illustrates the Metabolic Pathway toward Lutein in Red Algal Seaweeds

Abstract

Carotenoids are essential phytonutrients synthesized by all photosynthetic organisms. Acyclic lycopene is the first branching point for carotenoid biosynthesis. Lycopene βand ε-cyclases (LCYB and LCYE, respectively) catalyze the cyclization of its open ends and direct the metabolic flux into different downstream branches. Carotenoids of the β,β-branch (e.g., β-carotene) are found in all photosynthetic organisms, but those of the β,ε-branch (e.g., lutein) are generally absent in cyanobacteria, heterokonts, and some red algae. Although both LCYBs and LCYEs have been characterized from land plants, there are only a few reports on LCYs from cyanobacteria and algae. Here, we cloned four LCY genes from Porphyra umbilicalis and Pyropia yezoensis (susabi-nori) of Bangiales, the most primitive red algal order that synthesizes lutein. Our functional characterization in both Escherichia coli and Arabidopsis thaliana demonstrated that each species has a pair of LCYB and LCYE. Similar to LCYs from higher plants, red algal LCYBs cyclize both ends of lycopene, and their LCYEs only cyclize a single end. The characterization of LCYEs from red algae resolved the first bifurcation step toward β-carotene and lutein biosynthesis. Our phylogenetic analysis suggests that LCYEs of the green lineage and the red algae originated separately during evolution.

Biosynthesis and extraction of high-value carotenoid from algae

“…Macrophytic red algae have both LCYB and LCYE enzymes while microphytic algae have only the enzyme LCYB [52]. Some other studies also suggested that, synthesis of δ-carotene, α-carotene and lutein are absent in some groups of algae-like Bacillariophyceae, Chrysophyceae, Phaeophyceae, Xanthophyceae, and some red algae, while the β-carotene occurs in majority groups of algae and other photosynthetic organisms [18,58]. Liang et al [79] reported that the amino acid sequences of LCYB and LCYE are significantly similar.…”

“…In the case of red algae, Lohr et al [55] reported that both MVA and MEP pathways participate in the biosynthesis of IPP molecules. On the other hand, Deng et al [58] suggested that bioinformatics analyses are not able to characterize the genes for MVA pathway enzymes in red algae. Based on the existing ESTs, genome data, and phylogeny clustering analysis, Du et al [59] also reported that green algae and red algae received their plastid by primary endosymbiotic events with cyanobacteria, while brown algae obtained their plastid via secondary endosymbiotic event with red algae.…”

“…Lao et al [67] reported that, GGPPS of an alga Haematococcus pluvialis (HpGGPPS) have tri-functional catalytic activities, which catalyzes all three steps of GGPP biosynthesis. Deng et al [58] cloned and characterize the bfGGPPS from the red alga Bangia fuscopurpurea. They also report that GGPP is the only product of this enzyme and it also interacts with psy gene, which is the rate-limiting enzyme of the carotenoid biosynthesis pathway.…”

“…They also report that GGPP is the only product of this enzyme and it also interacts with psy gene, which is the rate-limiting enzyme of the carotenoid biosynthesis pathway. Deng et al [58] also performed the phylogeny analysis and suggest that the red algal and diatoms share a common ancestor for GGPPS but green algae and higher plants show an early divergence of GGPPS during evolution. It has been reported that, the supply of GGPP and its precursors decides the rate and subsequent flux of carotenoid biosynthesis in algae [68].…”

“…Similarly, β-carotene is also synthesized in two sequential steps, but here, both steps are catalyzes by the same enzyme LCYB. In the first step lycopene converted to γ-carotene and in the next step this γcarotene is converted to β-carotene [58].…”