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Molecular Structure and Enzymatic Function of Lycopene Cyclase from the Cyanobacterium Synechococcus sp Strain PCC 7942
| Content Provider | Semantic Scholar |
|---|---|
| Author | Cunningham, Francis X. Sun, Zairen Chamovitz, Daniel A. Hirschberg, Joseph Gantt, Elisabeth |
| Copyright Year | 2002 |
| Abstract | A gene encoding the enzyme lycopene cyclase in the cyanobacterium Synechococcus sp strain PCC7942 was mapped by genetic complementation, cloned, and sequenced. This gene, which we have named crtL, was expressed in strains of Escherichia col i that were genetically engineered to accumulate the carotenoid precursors lycopene, neurosporene, and C-carotene. The crtL gene product converts the acyclic hydrocarbon lycopene into the bicyclic p-carotene, an essentia1 component of the photosynthetic apparatus in oxygen-evolving organisms and a source of vitamin A in human and animal nutrition. The enzyme also converts neurosporene to the monocyclic p-zeacarotene but does not cyclize C-carotene, indicating that desaturation of the 7-8 or 7'-8' carbon-carbon bond is required for cyclization. The bleaching herbicide 2-(4-methylphenoxy)triethylamine hydrochloride (MPTA) effectively inhibits both cyclization reactions. A mutation that confers resistance to MPTA in Synechococcus sp PCC7942 was identified as a point mutation in the promoter region of crtL. The deduced amino acid sequence of lycopene cyclase specifies a polypeptide of 41 1 amino acids with a molecular weight of 46,125 anda p l of 6.0. An amino acid sequence motif indicative of FAD utilization is located at the N terminus of the polypeptide. DNA gel blot hybridization analysis indicated a single copy of crtL in Synechococcus sp PCC7942. Other than the FAD binding motif, the predicted amino acid sequence of the cyanobacterial lycopene cyclase bears little resemblance to the two known lycopene cyclase enzymes from nonphotosynthetic bacteria. Preliminary results from DNA gel blot hybridization experiments suggest that, like two earlier genes in the pathway, the Synechococcus gene encoding lycopene cyclase is homologous to plant and alga1 genes encoding this enzyme. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.plantcell.org/content/plantcell/6/8/1107.full.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
