Characterization of plant carotenoid cyclases as members of the flavoprotein family functioning with no net redox change

Alexis Samba Mialoundama, Dimitri Heintz, Nurul Jadid, Paul Nkeng, Alain Rahier, Jozsef Deli, Bilal Camara, Florence Bouvier*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

42 Citations (Scopus)


The later steps of carotenoid biosynthesis involve the formation of cyclic carotenoids. The reaction is catalyzed by lycopene b-cyclase (LCY-B), which converts lycopene into b-carotene, and by capsanthin-capsorubin synthase (CCS), which is mainly dedicated to the synthesis of k-cyclic carotenoids (capsanthin and capsorubin) but also has LCY-B activity. Although the peptide sequences of plant LCY-Bs and CCS contain a putative dinucleotide-binding motif, it is believed that these two carotenoid cyclases proceed via protic activation and stabilization of resulting carbocation intermediates. Using pepper (Capsicum annuum) CCS as a prototypic carotenoid cyclase, we show that the monomeric protein contains one noncovalently bound flavin adenine dinucleotide (FAD) that is essential for enzyme activity only in the presence of NADPH, which functions as the FAD reductant. The reaction proceeds without transfer of hydrogen from the dinucleotide cofactors to b-carotene or capsanthin. Using site-directed mutagenesis, amino acids potentially involved in the protic activation were identified. Substitutions of alanine, lysine, and arginine for glutamate-295 in the conserved 293-FLEET-297 motif of pepper CCS or LCY-B abolish the formation of b-carotene and k-cyclic carotenoids. We also found that mutations of the equivalent glutamate-196 located in the 194-LIEDT-198 domain of structurally divergent bacterial LCY-B abolish the formation of b-carotene. The data herein reveal plant carotenoid cyclases to be novel enzymes that combine characteristics of non-metal-assisted terpene cyclases with those attributes typically found in flavoenzymes that catalyze reactions, with no net redox, such as type 2 isopentenyl diphosphate isomerase. Thus, FAD in its reduced form could be implicated in the stabilization of the carbocation intermediate.

Original languageEnglish
Pages (from-to)970-979
Number of pages10
JournalPlant Physiology
Issue number3
Publication statusPublished - Jul 2010


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