Cloning and functional characterization of a lycopene β-cyclase from macrophytic red alga bangia fuscopurpurea

Abstract

Lycopene cyclases cyclize the open ends of acyclic lycopene (ψ ψ-carotene) into β-or "-ionone rings in the crucial bifurcation step of carotenoid biosynthesis. Among all carotenoid constituents, β-carotene (β,β-carotene) is found in all photosynthetic organisms, except for purple bacteria and heliobacteria, suggesting a ubiquitous distribution of lycopene β-cyclase activity in these organisms. In this work, we isolated a gene (BfLCYB) encoding a lycopene β-cyclase from Bangia fuscopurpurea, a red alga that is considered to be one of the primitive multicellular eukaryotic photosynthetic organisms and accumulates carotenoid constituents with both β-and "-rings, including β-carotene, zeaxanthin, a-carotene (β,"-carotene) and lutein. Functional complementation in Escherichia coli demonstrated that BfLCYB is able to catalyze cyclization of lycopene into monocyclic α-carotene (β,-carotene) and bicyclic β-carotene, and cyclization of the open end of monocyclic d-carotene (",-carotene) to produce a-carotene. No "-cyclization activity was identified for BfLCYB. Sequence comparison showed that BfLCYB shares conserved domains with other functionally characterized lycopene cyclases from different organisms and belongs to a group of ancient lycopene cyclases. Although B. fuscopurpurea also synthesizes a-carotene and lutein, its enzyme-catalyzing "-cyclization is still unknown.