InterPro domain: IPR010108

This family includes lycopene beta-and epsilion-cyclases, which are involved in the biosynthesis of carotenoids in bacteria and plants, and the related capsanthin capsorubin synthase (Ccs) from plants, which converts antheraxanthin or violaxanthin into capsanthin or capsorubin by a mechanism similar to lycopene cyclization. This family also includes neoxanthin synthase, which is involved in the synthesis of neoxanthin, the last product of carotenoid synthesis and a precursor of abscisic acid [ 1 ].

Lycopene cyclases generate provitamin A carotenoids which are essential building blocks for cyclic xanthophylls involved in photosynthesis and regulatory networks. The cyclization of lycopene is the final step in carotenoid biosynthesis and may proceed via one of two pathways: the formation of a beta ring by beta-cyclase, or an epsilon ring by epsilon-cyclase. Epsilon-cyclase adds only one ring, forming the monocyclic delta-carotene, whereas beta-cyclase introduces a ring at both ends of lycopene to form the bicyclic beta-carotene [ 2 ]. Lycopene cyclases are widely distributed across taxonomic groups and have structural diversity. Four partly related families of lycopene cyclases are known: CrtY, CrtL (beta-ionone end group producing), CrtL (eta-ionone end group producing) and CrtL (capsanthin/capsorubin synthase).

1. Identification of a novel gene coding for neoxanthin synthase from Solanum tuberosum. FEBS Lett. 485, 168-72
2. Functional analysis of the beta and epsilon lycopene cyclase enzymes of Arabidopsis reveals a mechanism for control of cyclic carotenoid formation. Plant Cell 8, 1613-26