title: Identification of a lycopene beta-cyclase required for bacteriorhodopsin biogenesis in the archaeon Halobacterium salinarum.
abstract: Biogenesis of the light-driven proton pump bacteriorhodopsin in the archaeon Halobacterium salinarum requires coordinate synthesis of the bacterioopsin apoprotein and carotenoid precursors of retinal, which serves as a covalently bound cofactor. As a step towards elucidating the mechanism and regulation of carotenoid metabolism during bacteriorhodopsin biogenesis, we have identified an H. salinarum gene required for conversion of lycopene to beta-carotene, a retinal precursor. The gene, designated crtY, is predicted to encode an integral membrane protein homologous to lycopene beta-cyclases identified in bacteria and fungi. To test crtY function, we constructed H. salinarum strains with in-frame deletions in the gene. In the deletion strains, bacteriorhodopsin, retinal, and beta-carotene were undetectable, whereas lycopene accumulated to high levels ( approximately 1.3 nmol/mg of total cell protein). Heterologous expression of H. salinarum crtY in a lycopene-producing Escherichia coli strain resulted in beta-carotene production. These results indicate that H. salinarum crtY encodes a functional lycopene beta-cyclase required for bacteriorhodopsin biogenesis. Comparative sequence analysis yields a topological model of the protein and provides a plausible evolutionary connection between heterodimeric lycopene cyclases in bacteria and bifunctional lycopene cyclase-phytoene synthases in fungi.
authors: Department of Biomolecular Chemistry, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
authors: Ronald F
authors: RF
authors: Peck
authors: Eric A
authors: EA
authors: Johnson
authors: Mark P
authors: MP
authors: Krebs
mesh_terms: D000595:Amino Acid Sequence; D001436:Bacteriorhodopsins / Q000096:biosynthesis*; D002338:Carotenoids / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D017353:Gene Deletion; D005822:Genetic Vectors; D019617:Halobacterium salinarum / Q000201:enzymology*; D019753:Intramolecular Lyases / Q000235:genetics / Q000378:metabolism*; D000077276:Lycopene; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000378:metabolism; D012172:Retinaldehyde / Q000096:biosynthesis; D016415:Sequence Alignment; D019207:beta Carotene / Q000096:biosynthesis
chemical_list: D011498:Protein Precursors; D019207:beta Carotene; D002338:Carotenoids; D001436:Bacteriorhodopsins; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase; D012172:Retinaldehyde; D000077276:Lycopene