2 Carotenoids in Phototrophic Microalgae …
29
Euglena gracilis (Sugiyama et al. 2020) and CrtH from Synechocystis sp. PCC 6803
(Masamoto et al. 2001; Breitenbach et al. 2001). The CrtP of Synechococcus elongatus PCC 7942 is stimulated by NAD(P) and oxygen as a possible final electron
acceptor (Schneider et al. 1997). CrtQ only from Anabaena sp. PCC 7120 showed
sequence homology with bacterial phytoene desaturase (CrtI) and CrtH (Linden et al.
1993), while other CrtQs show sequence homology with CrtP and plant CrtQ.
In contrast, the bacterial type uses only one enzyme, phytoene desaturase (CrtI), to
convert from phytoene to lycopene. The primitive cyanobacterium of Gloeobacter
violaceus PCC 7421 uses this type of CrtI, and homologous genes of crtP, crtQ
and crtH are not found in the genome (Steiger et al. 2005; Tsuchiya et al. 2005);
therefore, G. violaceus is the only oxygenic phototroph that has been shown to use
this type (Table 2.2). These observations suggest the following evolutionary scheme
for this step in the reaction: the desaturation of phytoene was initially carried out
by CrtI in ancestral cyanobacteria; crtP and related desaturase genes were acquired,
and ultimately, there was replacement of crtI by crtP occurred (Tsuchiya et al.
2005). Among anoxygenic phototrophs, purple bacteria, green filamentous bacteria,
heliobacteria, and newly identified Gemmatimonas use CrtI, whereas green sulfur
bacteria and newly identified Chloracidobacterium use CrtP, CrtQ and CrtH without
Z-ISO (Takaichi 2009, 2011; Sugiyama et al. 2020).
2.3.2 β-Carotene and α-Carotene Synthesis by Lycopene
Cyclases
All carotenoids in oxygenic phototrophs are dicyclic carotenoids, β-carotene, αcarotene, and their derivatives, and are derived from lycopene (Figs. 2.1 and 2.2).
Exceptionally, myxol glycosides and oscillol diglycosides in cyanobacteria are
monocyclic and acyclic carotenoids, respectively.
Lycopene is cyclized into either β-carotene via γ -carotene or α-carotene via
δ-carotene. Three distinct families of lycopene cyclases have been identified in
carotenogenic organisms (Krubasik and Sandmann 2000; Takaichi and Mochimaru
2007; Maresca et al. 2007). One large family contains CrtY, found in some bacteria,
except cyanobacteria, and CrtL (CrtL-b, Lcy-b), found in some cyanobacteria and
land plants. Lycopene ε-cyclases (CrtL-e, Lcy-e) from land plants are also included.
Their amino acid sequences exhibit five conserved regions (Krubasik and Sandmann 2000; Sandmann 2002; Ramos et al. 2008), and have an NAD(P)/FAD-binding
motif (Harker and Hirschberg 1998). Some CrtLs have been functionally confirmed
(Table 2.2). Note that Krubasik and Sandmann (2000) and Takaichi (2011) indicate
these are part of the same family, whereas Maresca et al. (2007) divide this family
into two CrtY and CrtL families.
Two cyanobacteria also contain CrtL-type enzymes (Table 2.2). Synechococcus
elongatus PCC 7942 contains a functional CrtL (Cunningham et al. 1994). Prochlorococcus marinus MED4 contains two lycopene cyclases, which exhibit sequence
29
Euglena gracilis (Sugiyama et al. 2020) and CrtH from Synechocystis sp. PCC 6803
(Masamoto et al. 2001; Breitenbach et al. 2001). The CrtP of Synechococcus elongatus PCC 7942 is stimulated by NAD(P) and oxygen as a possible final electron
acceptor (Schneider et al. 1997). CrtQ only from Anabaena sp. PCC 7120 showed
sequence homology with bacterial phytoene desaturase (CrtI) and CrtH (Linden et al.
1993), while other CrtQs show sequence homology with CrtP and plant CrtQ.
In contrast, the bacterial type uses only one enzyme, phytoene desaturase (CrtI), to
convert from phytoene to lycopene. The primitive cyanobacterium of Gloeobacter
violaceus PCC 7421 uses this type of CrtI, and homologous genes of crtP, crtQ
and crtH are not found in the genome (Steiger et al. 2005; Tsuchiya et al. 2005);
therefore, G. violaceus is the only oxygenic phototroph that has been shown to use
this type (Table 2.2). These observations suggest the following evolutionary scheme
for this step in the reaction: the desaturation of phytoene was initially carried out
by CrtI in ancestral cyanobacteria; crtP and related desaturase genes were acquired,
and ultimately, there was replacement of crtI by crtP occurred (Tsuchiya et al.
2005). Among anoxygenic phototrophs, purple bacteria, green filamentous bacteria,
heliobacteria, and newly identified Gemmatimonas use CrtI, whereas green sulfur
bacteria and newly identified Chloracidobacterium use CrtP, CrtQ and CrtH without
Z-ISO (Takaichi 2009, 2011; Sugiyama et al. 2020).
2.3.2 β-Carotene and α-Carotene Synthesis by Lycopene
Cyclases
All carotenoids in oxygenic phototrophs are dicyclic carotenoids, β-carotene, αcarotene, and their derivatives, and are derived from lycopene (Figs. 2.1 and 2.2).
Exceptionally, myxol glycosides and oscillol diglycosides in cyanobacteria are
monocyclic and acyclic carotenoids, respectively.
Lycopene is cyclized into either β-carotene via γ -carotene or α-carotene via
δ-carotene. Three distinct families of lycopene cyclases have been identified in
carotenogenic organisms (Krubasik and Sandmann 2000; Takaichi and Mochimaru
2007; Maresca et al. 2007). One large family contains CrtY, found in some bacteria,
except cyanobacteria, and CrtL (CrtL-b, Lcy-b), found in some cyanobacteria and
land plants. Lycopene ε-cyclases (CrtL-e, Lcy-e) from land plants are also included.
Their amino acid sequences exhibit five conserved regions (Krubasik and Sandmann 2000; Sandmann 2002; Ramos et al. 2008), and have an NAD(P)/FAD-binding
motif (Harker and Hirschberg 1998). Some CrtLs have been functionally confirmed
(Table 2.2). Note that Krubasik and Sandmann (2000) and Takaichi (2011) indicate
these are part of the same family, whereas Maresca et al. (2007) divide this family
into two CrtY and CrtL families.
Two cyanobacteria also contain CrtL-type enzymes (Table 2.2). Synechococcus
elongatus PCC 7942 contains a functional CrtL (Cunningham et al. 1994). Prochlorococcus marinus MED4 contains two lycopene cyclases, which exhibit sequence