Plant Carotene Cis-Trans Isomerase CRTISO

Abstract

The carotene cis-trans isomerase CRTISO is a constituent of the carotene desaturation pathway as evolved in cyanobacteria and prevailing in plants, in which a tetra-cis-lycopene species, termed prolycopene, is formed. CRTISO, an evolutionary descendant of the bacterial carotene desaturase CRTI, catalyzes the cis-to-trans isomerization reactions leading to all-trans-lycopene, the substrate for the subsequent lycopene cyclization to form all-trans-␣/␤-carotene. CRTISO and CRTI share a dinucleotide binding motif at the N terminus. Here we report that this site is occupied by FAD in CRTISO. The reduced form of this cofactor catalyzes a reaction not involving net redox changes. Results obtained with C(1)-and C(5)-deaza-FAD suggest mechanistic similarities with type II isopentenyl diphosphate: dimethylallyl diphosphate isomerase (IDI-2). CRTISO, together with lycopene cyclase CRTY and IDI-2, thus represents the third enzyme in isoprenoid metabolism belonging to the class of non-redox enzymes depending on reduced flavin for activity. The regional specificity and the kinetics of the isomerization reaction were investigated in vitro using purified enzyme and biphasic liposome-based systems carrying specific cis-configured lycopene species as substrates. The reaction proceeded from cis to trans, recognizing half-sides of the symmetrical prolycopene and was accompanied by one trans-to-cis isomerization step specific for the C(5)-C(6) double bond. Rice lycopene ␤-cyclase (OsLCY-b), when additionally introduced into the biphasic in vitro system used, was found to be stereospecific for all-trans-lycopene and allowed the CRTISO reaction to proceed toward completion by modifying the thermodynamics of the overall reaction.Carotenoids belong to a large isoprenoid family, some members of which are indispensible in all photosynthetic organisms; however, they can also be formed by some heterotrophic bacteria and fungi. In photosynthesis, carotenoids play an important role in light harvesting and in the protection of cells from photo damage caused by reactive oxygen species. In addition, some carotenoids are precursors of phytohormones such as abscisic acid (1) and the strigolactones (2, 3). In human nutrition, carotenoids containing at least one unsubstituted ␤-ionone ring serve as provitamin A carotenoids (for review, see Ref. 4). In recent years, a wealth of molecular information on carotenogenesis in plants and microorganisms has become available (see Refs. 5, 6 for reviews on plant carotenogenesis), however, information on the enzymology and biochemistry of the involved reactions is comparatively scarce.In the carotenoid biosynthetic pathway, phytoene is the first carotene formed. Phytoene is a colorless C 40 triene prenyl hydrocarbon, which undergoes four desaturation steps during which double bonds are introduced to finally form the fully conjugated undecaene chromophore of the red-colored lycopene (Fig. 1). There are two divergent classes of carotene desaturases catalyzing the formation of the identical product (all-trans-lyc...

Enzymatic study on AtCCD4 and AtCCD7 and their potential to form acyclic regulatory metabolites

“…S3F, G). Assuming a relevant contribution of CRTISO, which can generate partially trans -isomerized neurosporene and lycopene (Isaacson et al , 2004; Yu et al , 2011), we also assayed 9'- cis -neurosporene (Supplementary Fig. S3H).…”

“…Cleavage of 9- cis-ζ -carotene indicated an activity with 9'- cis -neurosporene that is half identical with ζ-carotene, while the second, more desaturated half corresponds to lycopene. To obtain this substrate, we used recombinant CRTISO that can produce the corresponding 9'-mono- cis isomer from the poly- cis -compounds proneurosporene and prolycopene (Isaacson et al , 2004; Yu et al , 2011). Incubation with AtCCD7 led to a single detectable product, most probably ζ-apo-10'-carotenal (P7), as verified by UV/VIS spectroscopic properties (Fig.…”

“…All- trans -neurosporene was obtained from Rhodovulum sulfidophilum (Hagemann et al , 1996). 9'- cis -Neurosporene was prepared enzymatically by CRTI according to Yu et al (2011) and using the substrate 7,9,9'-tri- cis -neurosporene isolated from tangerine fruit (Carey, et al , 1983). Synthetic 9- cis -lycopene was obtained from Buchem (The Netherlands).…”

Carotenoids in nature: insights from plants and beyond

“…The function of these cis-carotenoids remains largely unknown and it is easy to speculate that they could play a role as novel signalling molecules. Most recently, CRTISO was shown to be essential for establishing an equilibrium between cis and trans carotenoid isomers (Yu et al 2011). Perhaps CRTISO has other functions, such as to control the production of apocarotenoid precursors required for phytohormone biosynthesis (e.g.…”

“…The role of light in substituting for the absence of CRTISO activity in green tissues is under debate and now emerges as an exciting area of intense carotenoid research to unravel the elusive chemical mechanisms and regulatory nature associated with photoisomerisation ( Fig. 2) (Cunningham and Schiff 1985;Sandmann 1991;Park et al 2002;Isaacson et al 2004;Yu et al 2011).…”