title: Novel 9-cis/all-trans β-carotene isomerases from plastidic oil bodies in Dunaliella bardawil catalyze the conversion of all-trans to 9-cis β-carotene.
abstract: We identified and demonstrated the function of 9-cis/all-trans β-carotene isomerases in plastidic globules of Dunaliella bardawil, the species accumulating the highest levels of 9-cis β-carotene that is essential for humans. The halotolerant alga Dunaliella bardawil is unique in that it accumulates under light stress high levels of β-carotene in plastidic lipid globules. The pigment is composed of two major isomers: all-trans β-carotene, the common natural form of this pigment, and 9-cis β-carotene. The biosynthetic pathway of β-carotene is known, but it is not clear how the 9-cis isomer is formed. We identified in plastidic lipid globules that were isolated from D. bardawil two proteins with high sequence homology to the D27 protein-a 9-cis/all-trans β-carotene isomerase from rice (Alder et al. Science 335:1348-1351, 2012). The proteins are enriched in the oil globules by 6- to 17-fold compared to chloroplast proteins. The expression of the corresponding genes, 9-cis-βC-iso1 and 9-cis-βC-iso2, is enhanced under light stress. The synthetic proteins catalyze in vitro conversion of all-trans to 9-cis β-carotene. Expression of the 9-cis-βC-iso1 or of 9-cis-βC-iso2 genes in an E. coli mutant line that harbors β-carotene biosynthesis genes enhanced the conversion of all-trans into 9-cis β-carotene. These results suggest that 9-cis-βC-ISO1 and 9-cis-βC-ISO2 proteins are responsible for the formation of 9-cis β-carotene in D. bardawil under stress conditions.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, 90095-1569, USA.
authors.forename: Lital
authors.initials: L
authors.lastname: Davidi
authors.affiliation: Department of Biological Chemistry, The Weizmann Institute of Science, 76100, Rehovot, Israel. uri.pick@weizmann.ac.il.
authors.forename: Uri
authors.identifier: http://orcid.org/0000-0001-6776-082X
authors.initials: U
authors.lastname: Pick
mesh_terms: D002338:Carotenoids / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D066292:Lipid Droplets / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D018087:Plastids / Q000378:metabolism; D019207:beta Carotene / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D019207:beta Carotene; D002338:Carotenoids
keywords: 9-Cis/all-trans β-carotene isomerases; Dunaliella bardawil; Plastidic lipid globules