30
S. Takaichi
homology to CrtL. CrtL-b exhibits lycopene β-cyclase activity, while CrtL-e is a
bifunctional enzyme having both lycopene ε-cyclase and lycopene β-cyclase activities (Stickforth et al. 2003). The combination of these two cyclases allows the production of β-carotene, α-carotene, and ε-carotene. These enzymes may have originated
from the duplication of a single gene. The characteristics of this CrtL-e are somewhat
different from those in land plants (Cunningham and Gantt 2001). In addition, the
β-end groups of both β-carotene and α-carotene (left half) might be hydroxylated
by CrtR to zeaxanthin through β-cryptoxanthin and 3-hydroxy-α-carotene, respectively, in P. marinus. Acaryochloris marina MBIC 11017 produces (6S)-α-carotene,
which displays opposite chirality at C-6 to the usual (6R)-α-carotene, and contains
only one crtL-like gene from genome sequence (Takaichi et al. 2012).
The second family of lycopene cyclases contain a heterodimer (CrtYc and CrtYd)
from bacteria, a monomer (CrtYc-Yd) from bacteria and archaea, and fused and
bifunctional CrtYBs from fungi (Hemmi et al. 2003; Iniesta et al. 2008), but these
are not found in phototrophs.
At first, a new family of functional lycopene cyclase in the form of CruA was
identified in Chlorobaculum tepidum (green sulfur bacterium) (Maresca et al. 2005).
Homologous genes, cruA and cruP, have been found in the genome of Synechococcus
sp. PCC 7002, and their main products are γ -carotene in E. coli, which produces
lycopene (Maresca et al. 2007). On the other hand, Bradbury et al. (2012) have
reported that cruP of Synechococcus sp. PCC 7002 has not lycopene cyclase activity.
Recently, using lycopene producing E. coli, Sugiyama et al. (2017) reported that
CruA from Arthrospira platensis NIES-39 exhibits lycopene cyclase activity in E.
coli. Furthermore, Xiong et al. (2017) determined that CruA from Synechocystis
sp. PCC 6803 has lycopene cyclase activity requiring bound chlorophyll a in cruA
deletion mutant of Synechococcus sp. PCC 7002.
Homologous genes of cruA and cruP are widely distributed in the genome of some
cyanobacteria; however, information about the activities of these cruA- and cruP-like
genes are limited, as described above. Phylogenetic analysis of the functional CruA-,
CruP- and CrtL-type lycopene cyclases, and their homologs in cyanobacteria shows
that they form three individual clusters (Sugiyama and Takaichi 2020). Therefore,
further studies of distributions of functional lycopene cyclases (CrtL- and CruA-like,
or others) in cyanobacteria are required.
The distribution of α-carotene, CrtL-e, is limited in some algae classes (Table 2.1).
In some species of land plants, the characteristics of CrtL-e have been investigated
(Cunningham and Gantt 2001), and are shown to have sequence homology with
crtL-b. Lycopene is first converted to δ-carotene by CrtL-e, and then to α-carotene
by CrtL-b. γ -Carotene, produced by CrtL-b, is not a suitable substrate for CrtL-e
(Takaichi 2011).
S. Takaichi
homology to CrtL. CrtL-b exhibits lycopene β-cyclase activity, while CrtL-e is a
bifunctional enzyme having both lycopene ε-cyclase and lycopene β-cyclase activities (Stickforth et al. 2003). The combination of these two cyclases allows the production of β-carotene, α-carotene, and ε-carotene. These enzymes may have originated
from the duplication of a single gene. The characteristics of this CrtL-e are somewhat
different from those in land plants (Cunningham and Gantt 2001). In addition, the
β-end groups of both β-carotene and α-carotene (left half) might be hydroxylated
by CrtR to zeaxanthin through β-cryptoxanthin and 3-hydroxy-α-carotene, respectively, in P. marinus. Acaryochloris marina MBIC 11017 produces (6S)-α-carotene,
which displays opposite chirality at C-6 to the usual (6R)-α-carotene, and contains
only one crtL-like gene from genome sequence (Takaichi et al. 2012).
The second family of lycopene cyclases contain a heterodimer (CrtYc and CrtYd)
from bacteria, a monomer (CrtYc-Yd) from bacteria and archaea, and fused and
bifunctional CrtYBs from fungi (Hemmi et al. 2003; Iniesta et al. 2008), but these
are not found in phototrophs.
At first, a new family of functional lycopene cyclase in the form of CruA was
identified in Chlorobaculum tepidum (green sulfur bacterium) (Maresca et al. 2005).
Homologous genes, cruA and cruP, have been found in the genome of Synechococcus
sp. PCC 7002, and their main products are γ -carotene in E. coli, which produces
lycopene (Maresca et al. 2007). On the other hand, Bradbury et al. (2012) have
reported that cruP of Synechococcus sp. PCC 7002 has not lycopene cyclase activity.
Recently, using lycopene producing E. coli, Sugiyama et al. (2017) reported that
CruA from Arthrospira platensis NIES-39 exhibits lycopene cyclase activity in E.
coli. Furthermore, Xiong et al. (2017) determined that CruA from Synechocystis
sp. PCC 6803 has lycopene cyclase activity requiring bound chlorophyll a in cruA
deletion mutant of Synechococcus sp. PCC 7002.
Homologous genes of cruA and cruP are widely distributed in the genome of some
cyanobacteria; however, information about the activities of these cruA- and cruP-like
genes are limited, as described above. Phylogenetic analysis of the functional CruA-,
CruP- and CrtL-type lycopene cyclases, and their homologs in cyanobacteria shows
that they form three individual clusters (Sugiyama and Takaichi 2020). Therefore,
further studies of distributions of functional lycopene cyclases (CrtL- and CruA-like,
or others) in cyanobacteria are required.
The distribution of α-carotene, CrtL-e, is limited in some algae classes (Table 2.1).
In some species of land plants, the characteristics of CrtL-e have been investigated
(Cunningham and Gantt 2001), and are shown to have sequence homology with
crtL-b. Lycopene is first converted to δ-carotene by CrtL-e, and then to α-carotene
by CrtL-b. γ -Carotene, produced by CrtL-b, is not a suitable substrate for CrtL-e
(Takaichi 2011).