Carotenogenesis in cyanobacteria: CruA/CruP-type and CrtL-type lycopene cyclases

Abstract

Cyanobacteria are oxygenic photoautotrophic prokaryotes containing chlorophylls and carotenoids, and the latter play important roles in light-harvesting, protection of excess light, assembly of pigmentprotein complexes, and stabilization of lipid membranes. Cyanobacteria produce many kinds of carotenoids, such as β-carotene, zeaxanthin, echinenone, and myxol glycosides, which have a cyclic structure at one or both end(s). Cyclization of lycopene is a branch point in carotenoid biosynthesis to β-carotene and γ-carotene. Two types of lycopene cyclases, CruA/CruP-type and CrtL-type, are functionally confirmed in only five species, while homologous genes are found in the genomes of most cyanobacteria. This review summarizes the carotenogenesis pathways and the functional enzymes along with genes, focusing particularly on the cyclization of lycopene by distinct types of lycopene cyclases in cyanobacteria.

Introduction of the Carotenoid Biosynthesis α-Branch Into Synechocystis sp. PCC 6803 for Lutein Production

“…Thus, these data provide further evidence that cruA (sll0147) encodes the lycopene β-cyclase in Synechocystis. In contrast, for the paralog CruP no β-cyclase activity could be proven (Figure 1A; Sugiyama et al, 2017;Sugiyama and Takaichi, 2020). Rather, CruP seems to be involved in ROS scavenging processes (Bradbury et al, 2012).…”

“…The mevalonate (MEV) pathway takes place in the cytosol of plant cells, while the methyl-erythritol phosphate (MEP) pathway is localized in plastids ( Lichtenthaler et al, 1997 ). The first step in the carotenoid pathway per se is the synthesis of phytoene, which is then converted via several desaturation steps into lycopene, the branch-point for the generation of all other carotenoids ( Figure 1A ; Domonkos et al, 2013 ; Sugiyama and Takaichi, 2020 ). In principle, plants and cyanobacteria share the same lycopene synthesis pathway, but they differ in the subsequent cyclization steps ( Paniagua-Michel et al, 2012 ; Breitenbach et al, 2013 ).…”

Carotenoids from Cyanobacteria: Biotechnological Potential and Optimization Strategies

“…Cyanobacteria are able to synthesize a wide variety of terpenoids due to a complex but well-described biosynthetic pathway known as carotenogenesis ( Figure 1 ). The production of these compounds originates from geranylgeranyl pyrophosphate precursor [ 9 , 10 ]. A series of genes encode synthases, desaturases, cyclases, and hydroxylases responsible for the synthesis of carotenoids.…”

“…From lycopene, the major primary carotenoids are formed, α- and β-carotene. α-carotene is formed in a direct conversion by lycopene cyclase (CrtL or CruA), while β-carotene is derived from a γ-carotene in a two-step process performed by a lycopene cyclase (CrtL or CruA) [ 9 , 10 ]. From the three carotenoids, several xanthophylls can be formed as follows.…”

“…From zeaxanthin, both antheraxanthin and violaxanthin can be formed through a revertible activity of epoxidase and de-epoxidase in a process called the violaxanthin cycle. From zeaxanthin, it is also possible to form nostoxanthin by a hydroxylase (CrtG), while from violaxanthin, it is possible to form neoxanthin by a neoxanthin synthase (NSY) [ 9 , 10 ]. Moreover, astaxanthin can be produced using engineered cyanobacteria by the inclusion of a CrtR or a CrtW gene.…”