Isoprenoid Pyrophosphate-Dependent Transcriptional Regulation of Carotenogenesis in Corynebacterium glutamicum

Abstract

<i>Corynebacterium glutamicum</i> is a natural producer of the C50 carotenoid decaprenoxanthin. The <i>crtEcg0722crtBIYEb</i> operon comprises most of its genes for terpenoid biosynthesis. The MarR-type regulator encoded upstream and in divergent orientation of the carotenoid biosynthesis operon has not yet been characterized. This regulator, named CrtR in this study, is encoded in many actinobacterial genomes co-occurring with terpenoid biosynthesis genes. CrtR was shown to repress the <i>crt</i> operon of <i>C. glutamicum</i> since DNA microarray experiments revealed that transcript levels of <i>crt</i> operon genes were increased 10 to 70-fold in its absence. Transcriptional fusions of a promoter-less <i>gfp</i> gene with the <i>crt</i> operon and <i>crtR</i> promoters confirmed that CrtR represses its own gene and the <i>crt</i> operon. Gel mobility shift assays with purified His-tagged CrtR showed that CrtR binds to a region overlapping with the -10 and -35 promoter sequences of the <i>crt</i> operon. Isoprenoid pyrophosphates interfered with binding of CrtR to its target DNA, a so far unknown mechanism for regulation of carotenogenesis. The molecular details of protein-ligand interactions remain to be studied. Decaprenoxanthin synthesis by <i>C. glutamicum</i> wild type was enhanced 10 to 30-fold upon deletion of <i>crtR</i> and was decreased 5 to 6-fold as result of <i>crtR</i> overexpression. Moreover, deletion of <i>crtR</i> was shown as metabolic engineering strategy to improve production of native and non-native carotenoids including lycopene, β-carotene, C.p. 450 and sarcinaxanthin.