Cooperation of two carotene desaturases in the production of lycopene in Myxococcus xanthus.
In Myxococcus xanthus, all known carotenogenic genes are grouped together in the gene cluster carB-carA, except for one, crtIb (previously named carC). We show here that the first three genes of the carB operon, crtE, crtIa, and crtB, encode a geranygeranyl synthase, a phytoene desaturase, and a phytoene synthase, respectively. We demonstrate also that CrtIa possesses cis-to-trans isomerase activity, and is able to dehydrogenate phytoene, producing phytofluene and zeta-carotene. Unlike the majority of CrtI-type phytoene desaturases, CrtIa is unable to perform the four dehydrogenation events involved in converting phytoene to lycopene. CrtIb, on the other hand, is incapable of dehydrogenating phytoene and lacks cis-to-trans isomerase activity. However, the presence of both CrtIa and CrtIb allows the completion of the four desaturation steps that convert phytoene to lycopene. Therefore, we report a unique mechanism where two distinct CrtI-type desaturases cooperate to carry out the four desaturation steps required for lycopene formation. In addition, we show that there is a difference in substrate recognition between the two desaturases; CrtIa dehydrogenates carotenes in the cis conformation, whereas CrtIb dehydrogenates carotenes in the trans conformation.
Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, Spain. ainiesta@stanford.edu
Antonio A
AA
Iniesta
María
M
Cervantes
Francisco J
FJ
Murillo
D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002338:Carotenoids / Q000737:chemistry / Q000378:metabolism*; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D000077276:Lycopene; D008956:Models, Chemical; D015394:Molecular Structure; D016941:Myxococcus xanthus / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D009876:Operon; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D013053:Spectrophotometry; D013237:Stereoisomerism; D013379:Substrate Specificity
D001426:Bacterial Proteins; D007527:Isoenzymes; D002338:Carotenoids; D010088:Oxidoreductases; C022398:phytoene dehydrogenase; D019883:Alkyl and Aryl Transferases; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D000077276:Lycopene