关键词： Mycobacteria   Lipids   mel2   PDIM   TAG   Bioluminescence   Redox stress  

摘要： Using a high throughput genetic strategy, designated Random Inducible Controlled Expression (RICE), we identified the six gene mel2 locus in Mtb and M. marinum. Interestingly, three of the genes present in mel2 have similarities to bioluminescence genes. Similar to other bacterial bioluminescence systems, mel2 facilitates detoxification of reactive oxygen species (ROS). Through the use of thin layer chromatography (TLC) we demonstrate enhanced production of the cell wall virulence lipid, pthiocerol dimycoserosate (PDIM), in a Mtb mel2 mutant relative to the wild type strain in the presence of both H2O2 and diamide oxidative stresses. Furthermore, propionate toxicity assays revealed increased accumulation of triacylglycerol (TAG) in the mel2 mutant relative to wild type. These observations provide the first evidence that mel2 plays a critical role in Mtb lipid biosynthesis. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： Mycobacterium tuberculosis   Colony phenotype   Human macrophages infection   Capsule   PDIM   Virulence  

摘要： Mycobacterium tuberculosis (MTB) colony morphology was associated to the pathogen's virulence. We isolated a new MTB H37Rv smooth colony, which only appeared following human macrophages (MDM) infection. The new phenotype was Alcohol-Acid resistant, but devoid of a covering capsule and biofilm defective. We ascertained that there were no deletions in the Rv0096-Rv0101 PDIM Operon, but that its expression was repressed as compared to MTB wild type (wt). Its lipid composition displayed lower PDIM components and higher TAG as compared to wt. In MDM it induced the sigma factors sigB, sigI and sigL expression vs. synthetic medium culture, while it repressed other six sigma factors. It also induced, significantly more than wt, mprA, a mycobacterial persistence regulator. It was phagocytosed more than wt by MDM, where it grew significantly less, but persisted therein till 14 days infection. It induced significantly less IFN-gamma, IL-12 and IL-27 transcription than wt in infected MDM, while it increased the transcription of inducible NOS. It resided in mature, LAMP-3 positive phagolysosomes, where it never formed cords. This apparently "weaker" colony might represent an adaptive intracellular phenotype, whose infection may be less productive, but probably better equipped for a long lasting persistence in mildly activated host cells. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： 分枝杆菌   PDIM   脂质   致病机制  

摘要： 结核分枝杆菌(MycobacteriumTuberculosis,MTB)是导致人和动物结核病的病原体。MTB细胞壁成分复杂,功能多样,不但帮助分枝杆菌抵御外界不良的生活环境,同时在细菌逃逸宿主免疫攻击和致病过程中也发挥重要作用。脂质占细胞壁干重的60%以上,其高含量与细菌毒力密切相关。MTB不含内毒素,也不产生外毒素和侵袭性酶类,其致病性主要与占细胞壁干重60%以上的脂质成分密切相关。PDIM(phthioceroldimycocerosate)作为细胞壁组分中独特而重要的结构,在维持细菌正常结构上发挥重要作用。由于PDIM在细胞壁分布的广泛性,研究发现PDIM在病原体-宿主的相互作用过程中也扮演重要角色,尤其是在细菌的早期侵染及进入巨噬细胞环节中发挥积极作用。对PDIM重要致病和毒力损伤机制研究,不仅加深对病原体-宿主互作网络中的理解,还有望为结核病的治疗带来新的希望与突破。

关键词： Mycobacterium   Virulence   Vaccines   PDIM   PGL   Lipopeptide  

摘要： Mycobacterium bovis is an important pathogen of both domesticated and wild animals in many countries, and improved vaccines have great potential to assist in its control and eventual eradication. One of the hallmarks of members of the Mycobacterium tuberculosis complex, which includes both M. bovis and M. tuberculosis, is their ability to synthesise an impressive array of unique and complex lipids, many of which act as defensive, offensive or adaptive effectors of virulence.. For example, studies focussed on the development of rationally attenuated strains of both M. bovis and M. tuberculosis with efficacy as animal or human vaccines have shown that the phthiocerol dimycocerosates (PDIMs) and glycosylphenol-PDIM (phenolic glycolipid, PGL) are key virulence factors. The availability of the genome sequences for M. bovis and M. tuberculosis, together with mutants of these organisms carrying defects in lipid biosynthesis, and biochemical and molecular tools to dissect lipid biosynthesis pathways, has enabled developments in our understanding of the biosynthesis of PDIMs and PGL, as well as the possible roles played by PDIMs and PGL in virulence. In this article we review some of these developments, and also propose a cryptic lipid biosynthesis pathway in M. bovis and M. tuberculosis that may be involved in the production of an unrecognised, virulence-associated lipopeptide. (C) 2011 Elsevier B.V. All rights reserved.

摘要： Isolated in vitro more than half a century ago, the H37Rv strain of Mycobacterium tuberculosis still remains the strain of choice for the majority of laboratories conducting in vivo studies of TB pathogenesis. In this report we reveal that H37Rv is highly prone to losing the ability to synthesize the cell wall lipid phthiocerol dimycocerosate (PDIM) during extended periods of in vitro culture. In addition, H37Rv stocks that have been held in vitro for even a short length of time should be thought of as a heterogeneous population of PDIM-positive and PDIM-negative cell types. We demonstrate that after weekly subculture of PDIM-positive isolates over a period of 20 weeks, the proportion of PDIM-negative cells rises above 30%. That PDIM biosynthesis is negatively selected in vitro is evident from the broad range of mutation types we observe within cultures originating from a single PDIM-positive parental clone. Moreover, the appearance of these multiple mutation types coupled with an enhanced growth rate of PDIM-negative bacteria ensures that 'PDIM-less' clones rapidly dominate in vitro cultures. It has been known for almost a decade that strains of M. tuberculosis that lack PDIM are severely attenuated during in vivo infection. Therefore, the loss of PDIM raises a very serious issue in regard to the interpretation of putative virulence factors where heterogeneous parental cultures are potentially being compared in vivo to recombinant clones isolated within a PDIM-negative background. It is essential that researchers undertaking in vivo virulence studies confirm the presence of PDIM within all recombinant clones and the parental strains they are derived from.

关键词： Lipids  

摘要： The fatty acid biosynthesis (FAS-II) pathway in Mycobacterium tuberculosis generates long chain fatty acids that serve as the precursors to mycolic acids, essential components of the mycobacterial cell wall. Enzymes in the FAS-II pathway are thought to form one or more noncovalent multi-enzyme complexes within the cell, and a bacterial two-hybrid screen was used to search for missing components of the pathway and to furnish additional data on interactions involving these enzymes in vivo. Using the FAS-II beta-ketoacyl synthase, KasA, as bait, an extensive bacterial two-hybrid screen of a M. tuberculosis genome fragment library unexpectedly revealed a novel interaction between KasA and PpsB as well as PpsD, two polyketide modules involved in the biosynthesis of the virulence lipid phthiocerol dimycocerosate (PDIM). Sequence analysis revealed that KasA interacts with PpsB and PpsD in the region of the acyl carrier domain of each protein, raising the possibility that lipids could be transferred between the FAS-II and PDIM biosynthetic pathways. Subsequent studies utilizing purified proteins and radiolabeled lipids revealed that fatty acids loaded onto PpsB were transferred to KasA and also incorporated into long chain fatty acids synthesized using a Mycobacterium smegmatis lysate. These data suggest that in addition to producing PDIMs, the growing phthiocerol product can also be shuttled into the FAS-II pathway via KasA as an entry point for further elongation. Interactions between these biosynthetic pathways may exist as a simple means to increase mycobacterial lipid diversity, enhancing functionality and the overall complexity of the cell wall.

关键词： other bioactive products   lipids   carboxylic acid esters (acyclic compounds)  

摘要： ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

关键词： conjugate addition   alkyne addition   asymmetric synthesis   hydrosilylation   mycobacterium tuberculosis  

摘要： The first asymmetric synthesis of phthiocerol was achieved in 15 simple steps and 5.6% overall yield by applying three efficient catalytic transformations. The construction of building block 4 started with the copper/phosphoramidite-catalyzed asymmetric conjugate addition of Me 2Zn to cycloheptenone, followed by in situ ethylation. Baeyer Villiger oxidation using excess m-chloroperoxybenzoic acid (mCPBA) followed by treatment of the resulting lactone 7 with K2C03 in MeOH led to the formation of the linear product. Treatment with TBAF followed by a Fleming-Tamao oxidation using KHCO3 and H2O2, resulted in the formation of the corresponding hydroxy ketones, which could be separated by column chromatography affording 16 as a pure isomers.

关键词： lipid virulence factor   metabolic flux   pathogenesis   PDIM   sulfolipid-1  

摘要： Mycobacterium tuberculosis synthesizes specific polyketide lipids that interact with the host and are required for virulence. Using a mass spectrometric approach to simultaneously monitor hundreds of lipids, we discovered that the size and abundance of two lipid virulence factors, phthiocerol climycocerosate (PDIM) and sulfolipid-1 (SL-11), are controlled by the availability of a common precursor, methyl malonyl CoA (MMCoA). Consistent with this view, increased levels of MMCoA led to increased abundance and mass of both PDIM and SL-1. Furthermore, perturbation of MMCoA metabolism attenuated pathogen replication in mice. Importantly, we detected increased PDIM synthesis in bacteria growing within host tissues and in bacteria grown in culture on odd-chain fatty acids. Because M. tuberculosis catabolizes host lipids to grow during infection, we propose that growth of M. tuberculosis on fatty acids in vivo leads to increased flux of MMCoA through lipid biosynthetic pathways, resulting in increased virulence lipid synthesis. Our results suggest that the shift to host lipid catabolism during infection allows for increased virulence lipid anabolism by the bacterium.

关键词： ACP   acyl carrier protein   AT   acyltransferase   CFU   colony forming unit   dextro   dextrorotatory   DIM   dimycocerosate ester   dPGL   deacylated phenolic glycolipid   DH   dehydratase   ER   enoyl-ACP reductase   hyg   hygromycin   km   kanamycin   KR   ketoreductase   KS   keto-acyl ACP synthase   levo   levorotatory   MalCoA   malonyl CoA   MeMalCoA   methyl malonyl CoA   Mbov   Mycobacterium bovis   Mgas   M. gastri   Mhae   M. haemophilum   Mkan   M. kansasii   Mlep   M. leprae   Mmar   M. marinum   Mtb   M. tuberculosis   Mulc   M. ulcerans   MYCS   mycocerosic acids   PDIM   phthiocerol dimycocerosate   PGL   phenolic glycolipid   PCOL   phthiocerol   ϕ   PCOL   phenolphthiocerol   PDON   phthiodiolone   PTOL   phthiotriol   SAM   S-adenosyl methionine   STM   signature tagged mutagenesis   wt   wild-type  

摘要： Recent advances in the study of mycobacterial lipids indicate that the class of outer membrane lipids known as dimycocerosate esters (DIMs) are major virulence factors of clinically relevant mycobacteria including Mycobacterium tuberculosis and Mycobacterium leprae. DIMs are a structurally intriguing class of polyketide synthase-derived wax esters discovered over seventy years ago, yet, little was known until recently about their biosynthesis. Availability of several mycobacterial genomes has accelerated progress toward clarifying steps in the DIM biosynthetic pathway and it is our belief that reviewing the bases of our current knowledge will clarify outstanding issues and help direct future endeavors. (C) 2005 Elsevier Ltd. All rights reserved.