The Biosynthetic Pathway for Myxol-2′ Fucoside (Myxoxanthophyll) in the Cyanobacterium <i>Synechococcus</i> sp. Strain PCC 7002

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:italic>Synechococcus</jats:italic> sp. strain PCC 7002 produces a variety of carotenoids, which comprise predominantly dicylic β-carotene and two dicyclic xanthophylls, zeaxanthin and synechoxanthin. However, this cyanobacterium also produces a monocyclic myxoxanthophyll, which was identified as myxol-2′ fucoside. Compared to the carotenoid glycosides produced by diverse microorganisms, cyanobacterial myxoxanthophyll and closely related compounds are unusual because they are glycosylated on the 2′-OH rather than on the 1′-OH position of the ψ end of the molecule. In this study, the genes encoding two enzymes that modify the ψ end of myxoxanthophyll in <jats:italic>Synechococcus</jats:italic> sp. strain PCC 7002 were identified. Mutational and biochemical studies showed that open reading frame SynPCC7002_A2032, renamed <jats:italic>cruF</jats:italic> , encodes a 1′-hydroxylase and that open reading frame SynPCC7002_A2031, renamed <jats:italic>cruG</jats:italic> , encodes a 2′-O-glycosyltransferase. The enzymatic activity of CruF was verified by chemical characterization of the carotenoid products synthesized when <jats:italic>cruF</jats:italic> was expressed in a lycopene-producing strain of <jats:italic>Escherichia coli</jats:italic> . Database searches showed that homologs of <jats:italic>cruF</jats:italic> and <jats:italic>cruG</jats:italic> occur in the genomes of all sequenced cyanobacterial strains that are known to produce myxol or the acylic xanthophyll oscillaxanthin. The genomes of many other bacteria that produce hydroxylated carotenoids but do not contain <jats:italic>crtC</jats:italic> homologs also contain <jats:italic>cruF</jats:italic> orthologs. Based upon observable intermediates, a complete biosynthetic pathway for myxoxanthophyll is proposed. This study expands the suite of enzymes available for metabolic engineering of carotenoid biosynthetic pathways for biotechnological applications. </jats:p>