Function
Dehydrogenase; part of the gene cluster that mediates the biosynthesis of the mycotoxin citrinin, a hepato-nephrotoxic compound to humans due to inhibition of respiration complex III (Ref.1). The pathway begins with the synthesis of a keto-aldehyde intermediate by the citrinin PKS (pksCT also named citS) from successive condensations of 4 malonyl-CoA units, presumably with a simple acetyl-CoA starter unit (Ref.1). Release of the keto-aldehyde intermediate is consistent with the presence of the C-terminal reductive release domain (Ref.1). The exact catalytic role of the hydrolase citA remains mysterious, although it is clear that it increases the productivity of the PKS and performs the earliest non-PKS step during citrinin biosynthesis (Ref.1). CitB then catalyzes the oxidation of the C-12 methyl of the ketone intermediate to an alcohol intermediate which is further oxidized by the oxidoreductase citC to produce a bisaldehyde intermediate (Ref.1). The fourth catalytic step is catalyzed by the citD aldehyde dehydrogenase (Ref.1). The final transformation is the reduction of C-3 by citE to provide the chemically stable citrinin nucleus (Ref.1). CitE appears highly selective for its substrate as its presence in any context other than a full complement of citS and citA-D does not result in observable new compounds (Ref.1).
Sequence
MATVKVIDFIQTPFDFLIVGGGTAGLVLAARLSEEPGIQVGVIEAGSLRLGDPKVDLPTGPGQMLGDPGYDWNFESIPQAGANAKAYHIPRGRMLGGSSGINFMSYNRPSAEDIDDWANKLGVKGWTWSELLPYFKRSENLEPIEPSASCPVSPKVHGTGGPIHTSIGPWQAPIEESLLAAFDEAARLQRPAEPYSGAHLGFYRSLFTLDRTSTPVRSYAVSGYYAPVMGRPNLKVLENAQVCRILLSDASDGIPVAEGVELHHAGARYAVSARREVILSAGSVQSPQLLELSGIGDPSVLEGAGIACRVANTDVGSNLQEHTMSAVSYECADGIMSVDSLFKDPALLEEHQSLYAKNHSGALSGSVSLMGFTPYSSLSTETQVDATMARIFDAPSVSGRLSQQNASYQRRQQEAVAARMQNRWSADIQFIGTPAYFNTAAGYASCAKIMSGPPVGYSACYSIVVSNMYPLSRGSVHVRTSNPMDAPAIDPGFLSHPVDVDVLAAGIVFADRVFRSTLLNGKVRRRVSPPAGLDLSNMDEARQFVRNHIVPYHHALGTCAMGQVVDEKLRVKGVRRLRVVDASVMPMQVSAAIMATVYAIAERASDIIKKDCGFGRRLRAHI