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Identification of phthiodiolone ketoreductase, an enzyme required for production of mycobacterial diacyl phthiocerol virulence factors.

ABSTRACT: Diacyl phthiocerol esters and their congeners are mycobacterial virulence factors. The biosynthesis of these complex lipids remains poorly understood. Insight into their biosynthesis will aid the development of rationally designed drugs that inhibit their production. In this study, we investigate a biosynthetic step required for diacyl (phenol)phthiocerol ester production, i.e., the reduction of the keto group of (phenol)phthiodiolones. We utilized comparative genomics to identify phthiodiolone ketoreductase gene candidates and provide a genetic analysis demonstrating gene function for two of these candidates. Moreover, we present data confirming the existence of a diacyl phthiotriol intermediate in diacyl phthiocerol biosynthesis. We also elucidate the mechanism underlying diacyl phthiocerol deficiency in some mycobacteria, such as Mycobacterium ulcerans and Mycobacterium kansasii. Overall, our findings shed additional light on the biosynthesis of an important group of mycobacterial lipids involved in virulence.

SUBMITTER: Onwueme KC

PROVIDER: S-EPMC1169502 | biostudies-literature | 2005 Jul

REPOSITORIES: biostudies-literature

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Identification of phthiodiolone ketoreductase, an enzyme required for production of mycobacterial diacyl phthiocerol virulence factors.

Onwueme Kenolisa C KC Vos Cheryl J CJ Zurita Juan J Soll Clifford E CE Quadri Luis E N LE

Journal of bacteriology 20050701 14

Diacyl phthiocerol esters and their congeners are mycobacterial virulence factors. The biosynthesis of these complex lipids remains poorly understood. Insight into their biosynthesis will aid the development of rationally designed drugs that inhibit their production. In this study, we investigate a biosynthetic step required for diacyl (phenol)phthiocerol ester production, i.e., the reduction of the keto group of (phenol)phthiodiolones. We utilized comparative genomics to identify phthiodiolone ...[more]

PMID: 15995190

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Project description:Phthiocerol dimycocerosates (PDIM) are a group of cell surface-associated apolar lipids of Mycobacterium tuberculosis and closely related mycobacteria, such as Mycobacterium bovis and Mycobacterium leprae A characteristic methoxy group of these lipids is generated from the methylation of a hydroxyl group of the direct precursors, the phthiotriols. The precursors arise from the reduction of phthiodiolones, the keto intermediates, by a ketoreductase. The putative phthiodiolone ketoreductase (PKR) is encoded by Rv2951c in M. tuberculosis and BCG_2972c in M. bovis BCG, and these open reading frames (ORFs) encode identical amino acid sequences. We investigated the cofactor requirement of the BCG_2972c protein. A comparative analysis based on the crystallographic structures of similar enzymes identified structural elements for binding of coenzyme F420 and hydrophobic phthiodiolones in PKR. Coenzyme F420 is a deazaflavin coenzyme that serves several key functions in pathogenic and nonpathogenic mycobacteria. We found that an M. bovis BCG mutant lacking F420-dependent glucose-6-phosphate dehydrogenase (Fgd), which generates F420H2 (glucose-6-phosphate + F420 ? 6-phosphogluconate + F420H2), was devoid of phthiocerols and accumulated phthiodiolones. When the mutant was provided with F420H2, a broken-cell slurry of the mutant converted accumulated phthiodiolones to phthiocerols; F420H2 was generated in situ from F420 and glucose-6-phosphate by the action of Fgd. Thus, the reaction mixture was competent in reducing phthiodiolones to phthiotriols (phthiodiolones + F420H2 ? phthiotriols + F420), which were then methylated to phthiocerols. These results established the mycobacterial phthiodiolone ketoreductase as an F420H2-dependent enzyme (fPKR). A phylogenetic analysis of close homologs of fPKR revealed potential F420-dependent lipid-modifying enzymes in a broad range of mycobacteria.Mycobacterium tuberculosis is the causative agent of tuberculosis, and phthiocerol dimycocerosates (PDIM) protect this pathogen from the early innate immune response of an infected host. Thus, the PDIM synthesis system is a potential target for the development of effective treatments for tuberculosis. The current study shows that a PDIM synthesis enzyme is dependent on the coenzyme F420 F420 is universally present in mycobacteria and absent in humans. This finding expands the number of experimentally validated F420-dependent enzymes in M. tuberculosis to six, each of which helps the pathogen to evade killing by the host immune system, and one of which activates an antituberculosis drug, PA-824. This work also has relevance to leprosy, since similar waxy lipids are found in Mycobacterium leprae.

Project description:Respiratory melioidosis is a disease presentation of the biodefense pathogen, Burkholderia pseudomallei, which is frequently associated with a lethal septicemic spread of the bacteria. We have recently developed an improved respiratory melioidosis model to study the pathogenesis of Burkholderia pseudomallei in the lung (intubation-mediated intratracheal [IMIT] inoculation), which more closely models descriptions of human melioidosis, including prominent septicemic spread from the lung and reduced involvement of the upper respiratory tract. We previously demonstrated that the Type 3 Secretion System cluster 3 (T3SS3) is a critical virulence determinant for B. pseudomallei when delivered directly into the lung. We decided to comprehensively identify all virulence determinants required for respiratory melioidosis using the Tn-seq phenotypic screen, as well as to investigate which virulence determinants are required for dissemination to the liver and spleen. While previous studies have used Tn-seq to identify essential genes for in vitro cultured B. pseudomallei, this represents the first study to use Tn-seq to identify genes required for in vivo fitness. Consistent with our previous findings, we identified T3SS3 as the largest genetic cluster required for fitness in the lung. Furthermore, we identified capsular polysaccharide and Type 6 Secretion System cluster 5 (T6SS5) as the two additional major genetic clusters facilitating respiratory melioidosis. Importantly, Tn-seq did not identify additional, novel large genetic systems supporting respiratory melioidosis, although these studies identified additional small gene clusters that may also play crucial roles in lung fitness. Interestingly, other previously identified virulence determinants do not appear to be required for lung fitness, such as lipopolysaccharide. The role of T3SS3, capsule, and T6SS5 in lung fitness was validated by competition studies, but only T3SS3 was found to be important for respiratory melioidosis when delivered as a single strain challenge, suggesting that competition studies may provide a higher resolution analysis of fitness factors in the lung. The use of Tn-seq phenotypic screening also provided key insights into the selective pressure encountered in the liver.

Dataset Information

Identification of phthiodiolone ketoreductase, an enzyme required for production of mycobacterial diacyl phthiocerol virulence factors.

Publications

Identification of phthiodiolone ketoreductase, an enzyme required for production of mycobacterial diacyl phthiocerol virulence factors.

Similar Datasets

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