Evidence of a Role for LytB in the Nonmevalonate Pathway of Isoprenoid Biosynthesis

Abstract

ABSTRACT It is proposed that the lytB gene encodes an enzyme of the deoxyxylulose-5-phosphate (DOXP) pathway that catalyzes a step at or subsequent to the point at which the pathway branches to form isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). A mutant of the cyanobacterium Synechocystis strain PCC 6803 with an insertion in the promoter region of lytB grew slowly and produced greenish-yellow, easily bleached colonies. Insertions in the coding region of lytB were lethal. Supplementation of the culture medium with the alcohol analogues of IPP and DMAPP (3-methyl-3-buten-1-ol and 3-methyl-2-buten-1-ol) completely alleviated the growth impairment of the mutant. The Synechocystis lytB gene and a lytB cDNA from the flowering plant Adonis aestivalis were each found to significantly enhance accumulation of carotenoids in Escherichia coli engineered to produce these colored isoprenoid compounds. When combined with a cDNA encoding deoxyxylulose-5-phosphate synthase ( dxs ), the initial enzyme of the DOXP pathway, the individual salutary effects of lytB and dxs were multiplied. In contrast, the combination of lytB and a cDNA encoding IPP isomerase ( ipi ) was no more effective in enhancing carotenoid accumulation than ipi alone, indicating that the ratio of IPP and DMAPP produced via the DOXP pathway is influenced by LytB.