Comprehensive essentiality analysis of the Mycobacterium kansasii genome by saturation transposon mutagenesis and deep sequencing.

Mycobacterium kansasii (Mk) is an opportunistic pathogen that is frequently isolated from urban water systems, posing a health risk to susceptible individuals. Despite its ability to cause tuberculosis-like pulmonary disease, very few studies have probed the genetics of this opportunistic pathogen. Here, we report a comprehensive essentiality analysis of the Mk genome. Deep sequencing of a high-density library of Mk Himar1 transposon mutants revealed that 86.8% of the chromosomal thymine-adenine (TA) dinucleotide target sites were permissive to insertion, leaving 13.2% TA sites unoccupied. Our analysis identified 394 of the 5,350 annotated open reading frames (ORFs) as essential. The majority of these essential ORFs (84.8%) share essential mutual orthologs with Mycobacterium tuberculosis (Mtb). A comparative genomics analysis identified 139 Mk essential ORFs that share essential orthologs in four other species of mycobacteria. Thirteen Mk essential ORFs share orthologs in all four species that were identified as being not essential, while only two Mk essential ORFs are absent in all species compared. We used the essentiality data and a comparative genomics analysis reported here to highlight differences in essentiality between candidate Mtb drug targets and the corresponding Mk orthologs. Our findings suggest that the Mk genome encodes redundant or additional pathways that may confound validation of potential Mtb drugs and drug target candidates against the opportunistic pathogen. Additionally, we identified 57 intergenic regions containing four or more consecutive unoccupied TA sites. A disproportionally large number of these regions were located upstream of pe/ppe genes. Finally, we present an essentiality and orthology analysis of the Mk pRAW-like plasmid, pMK1248. IMPORTANCE Mk is one of the most common nontuberculous mycobacterial pathogens associated with tuberculosis-like pulmonary disease. Drug resistance emergence is a threat to the control of Mk infections, which already requires long-term, multidrug courses. A comprehensive understanding of Mk biology is critical to facilitate the development of new and more efficacious therapeutics against Mk. We combined transposon-based mutagenesis with analysis of insertion site identification data to uncover genes and other genomic regions required for Mk growth. We also compared the gene essentiality data set of Mk to those available for several other mycobacteria. This analysis highlighted key similarities and differences in the biology of Mk compared to these other species. Altogether, the genome-wide essentiality information generated and the results of the cross-species comparative genomics analysis represent valuable resources to assist the process of identifying and prioritizing potential Mk drug target candidates and to guide future studies on Mk biology.

Genetic Underpinnings of Carotenogenesis and Light-Induced Transcriptome Remodeling in the Opportunistic Pathogen Mycobacterium kansasii.

Mycobacterium kansasii (Mk) causes opportunistic pulmonary infections with tuberculosis-like features. The bacterium is well known for its photochromogenicity, i.e., the production of carotenoid pigments in response to light. The genetics defining the photochromogenic phenotype of Mk has not been investigated and defined pigmentation mutants to facilitate studies on the role of carotenes in the bacterium's biology are not available thus far. In this study, we set out to identify genetic determinants involved in Mk photochromogenicity. We screened a library of ~150,000 transposon mutants for colonies with pigmentation abnormalities. The screen rendered a collection of ~200 mutants. Each of these mutants could be assigned to one of four distinct phenotypic groups. The insertion sites in the mutant collection clustered in three chromosomal regions. A combination of phenotypic analysis, sequence bioinformatics, and gene expression studies linked these regions to carotene biosynthesis, carotene degradation, and monounsaturated fatty acid biosynthesis. Furthermore, introduction of the identified carotenoid biosynthetic gene cluster into non-pigmented Mycobacterium smegmatis endowed the bacterium with photochromogenicity. The studies also led to identification of MarR-type and TetR/AcrR-type regulators controlling photochromogenicity and carotenoid breakdown, respectively. Lastly, the work presented also provides a first insight into the Mk transcriptome changes in response to light.

Mycobacterium abscessus Mutants with a Compromised Functional Link between the Type VII ESX-3 System and an Iron Uptake Mechanism Reliant on an Unusual Mycobactin Siderophore.

The opportunistic pathogen Mycobacterium abscessus subsp. abscessus (Mab) has become an emerging public health threat due to the increasing number of Mab-associated chronic pulmonary disease cases. Treatment requires multiple drug courses and is often combined with surgical resection. Cure rates are only ~50% due to treatment failure and comorbidities. Deeper understanding of the biology of Mab is required to illuminate potential avenues for the development of better therapeutics against Mab infections. The ESX-3 type VII protein secretion system of Mab has an important role in host inflammatory and pathological responses during infection. In this work, we demonstrate a functional link between ESX-3 and an iron uptake system based on an unusual mycobactin-type siderophore (designated MBT Ab) and exploit this link to implement a large screen for transposon mutants with an impaired ESX-3. Most mutants we identified carry insertions in genes encoding predicted ESX-3 secretion machinery components or potential ESX-3 substrates. The mutants overproduce MBT Ab, a trait consistent with an iron uptake defect. Our characterization of MBT Ab revealed structural features reminiscent of nocardial mycobactin-like compounds with cytotoxicity. This finding raises the possibility that MBT Ab may play roles in pathogenesis unlinked to iron homeostasis. The mutants generated herein will facilitate research to better understand the role of ESX-3 and its interplay with the siderophore system.

Transposon mutagenesis in Mycobacterium kansasii links a small RNA gene to colony morphology and biofilm formation and identifies 9,885 intragenic insertions that do not compromise colony outgrowth.

Mycobacterium kansasii (Mk) is a resilient opportunistic human pathogen that causes tuberculosis-like chronic pulmonary disease and mortality stemming from comorbidities and treatment failure. The standard treatment of Mk infections requires costly, long-term, multidrug courses with adverse side effects. The emergence of drug-resistant isolates further complicates the already challenging drug therapy regimens and threatens to compromise the future control of Mk infections. Despite the increasingly recognized global burden of Mk infections, the biology of this opportunistic pathogen remains essentially unexplored. In particular, studies reporting gene function or generation of defined mutants are scarce. Moreover, no transposon (Tn) mutagenesis tool has been validated for use in Mk, a situation limiting the repertoire of genetic approaches available to accelerate the dissection of gene function and the generation of gene knockout mutants in this poorly characterized pathogen. In this study, we validated the functionality of a powerful Tn mutagenesis tool in Mk and used this tool in conjunction with a forward genetic screen to establish a previously unrecognized role of a conserved mycobacterial small RNA gene of unknown function in colony morphology features and biofilm formation. We also combined Tn mutagenesis with next-generation sequencing to identify 12,071 Tn insertions that do not compromise viability in vitro. Finally, we demonstrated the susceptibility of the Galleria mellonella larva to Mk, setting the stage for further exploration of this simple and economical infection model system to the study of this pathogen.

Kinetic Analyses of the Siderophore Biosynthesis Inhibitor Salicyl-AMS and Analogues as MbtA Inhibitors and Antimycobacterial Agents.

There is a paramount need for expanding the drug armamentarium to counter the growing problem of drug-resistant tuberculosis. Salicyl-AMS, an inhibitor of salicylic acid adenylation enzymes, is a first-in-class antibacterial lead compound for the development of tuberculosis drugs targeting the biosynthesis of salicylic-acid-derived siderophores. In this study, we determined the Ki of salicyl-AMS for inhibition of the salicylic acid adenylation enzyme MbtA from Mycobacterium tuberculosis (MbtAtb), designed and synthesized two new salicyl-AMS analogues to probe structure-activity relationships (SAR), and characterized these two analogues alongside salicyl-AMS and six previously reported analogues in biochemical and cell-based studies. The biochemical studies included determination of kinetic parameters ( Kiapp, konapp, koff, and tR) and analysis of the mechanism of inhibition. For these studies, we optimized production and purification of recombinant MbtAtb, for which Km and kcat values were determined, and used the enzyme in conjunction with an MbtAtb-optimized, continuous, spectrophotometric assay for MbtA activity and inhibition. The cell-based studies provided an assessment of the antimycobacterial activity and postantibiotic effect of the nine MbtAtb inhibitors. The antimycobacterial properties were evaluated using a strain of nonpathogenic, fast-growing Mycobacterium smegmatis that was genetically engineered for MbtAtb-dependent susceptibility to MbtA inhibitors. This convenient model system greatly facilitated the cell-based studies by bypassing the methodological complexities associated with the use of pathogenic, slow-growing M. tuberculosis. Collectively, these studies provide new information on the mechanism of inhibition of MbtAtb by salicyl-AMS and eight analogues, afford new SAR insights for these inhibitors, and highlight several suitable candidates for future preclinical evaluation.

Mycobacteria Encode Active and Inactive Classes of TesB Fatty-Acyl CoA Thioesterases Revealed through Structural and Functional Analysis.

Mycobacteria contain a large number of highly divergent species and exhibit unusual lipid metabolism profiles, believed to play important roles in immune invasion. Thioesterases modulate lipid metabolism through the hydrolysis of activated fatty-acyl CoAs; multiple copies are present in mycobacteria, yet many remain uncharacterized. Here, we undertake a comprehensive structural and functional analysis of a TesB thioesterase from Mycobacterium avium (MaTesB). Structural superposition with other TesB thioesterases reveals that the Asp active site residue, highly conserved across a wide range of TesB thioesterases, is mutated to Ala. Consistent with these structural data, the wild-type enzyme failed to hydrolyze an extensive range of acyl-CoA substrates. Mutation of this residue to an active Asp residue restored activity against a range of medium-chain length fatty-acyl CoA substrates. Interestingly, this Ala mutation is highly conserved across a wide range of Mycobacterium species but not found in any other bacteria or organism. Our structural homology analysis revealed that at least one other TesB acyl-CoA thioesterase also contains an Ala residue at the active site, while two other Mycobacterium TesB thioesterases harbor an Asp residue at the active site. The inactive TesBs display a common quaternary structure that is distinct from that of the active TesB thioesterases. Investigation of the effect of expression of either the catalytically active or inactive MaTesB in Mycobacterium smegmatis exposed, to the best of our knowledge, the first genotype-phenotype association implicating a mycobacterial tesB gene. This is the first report that mycobacteria encode active and inactive forms of thioesterases, the latter of which appear to be unique to mycobacteria.

Design, synthesis, and biological evaluation of α-hydroxyacyl-AMS inhibitors of amino acid adenylation enzymes.

Biosynthesis of bacterial natural-product virulence factors is emerging as a promising antibiotic target. Many such natural products are produced by nonribosomal peptide synthetases (NRPS) from amino acid precursors. To develop selective inhibitors of these pathways, we have previously described aminoacyl-AMS (sulfamoyladenosine) macrocycles that inhibit NRPS amino acid adenylation domains but not mechanistically-related aminoacyl-tRNA synthetases. To improve the cell permeability of these inhibitors, we explore herein replacement of the α-amino group with an α-hydroxy group. In both macrocycles and corresponding linear congeners, this leads to decreased biochemical inhibition of the cysteine adenylation domain of the Yersina pestis siderophore synthetase HMWP2, which we attribute to loss of an electrostatic interaction with a conserved active-site aspartate. However, inhibitory activity can be regained by installing a cognate ß-thiol moiety in the linear series. This provides a path forward to develop selective, cell-penetrant inhibitors of the biosynthesis of virulence factors to probe their biological functions and potential as therapeutic targets.

Pleiotropic consequences of gene knockouts in the phthiocerol dimycocerosate and phenolic glycolipid biosynthetic gene cluster of the opportunistic human pathogen Mycobacterium marinum.

Phthiocerol dimycocerosates (PDIMs) and phenolic glycolipids (PGLs) contribute to the pathogenicity of several mycobacteria. Biosynthesis of these virulence factors requires polyketide synthases and other enzymes that represent potential targets for the development of adjuvant antivirulence drugs. We used six isogenic Mycobacterium marinum mutants, each with a different gene knockout in the PDIM/PGL biosynthetic pathway, to probe the pleiotropy of mutations leading to PDIM(-) PGL(-), PDIM(+) PGL(-) or PDIM(-) PGL(+) phenotypes. We evaluated the M. marinum mutants for changes in antibiotic susceptibility, cell envelope permeability, biofilm formation, surface properties, sliding motility and virulence in an amoeba model. The analysis also permitted us to begin exploring the hypothesis that different gene knockouts rendering the same PDIM and/or PGL deficiency phenotypes lead to M. marinum mutants with equivalent pleiotropic profiles. Overall, the results of our study revealed a complex picture of pleiotropic patterns emerging from different gene knockouts, uncovered unexpected phenotypic inequalities between mutants, and provided new insight into the phenotypic consequences of gene knockouts in the PDIM/PGL biosynthetic pathway.

Biosynthesis of cell envelope-associated phenolic glycolipids in Mycobacterium marinum.

Phenolic glycolipids (PGLs) are polyketide synthase-derived glycolipids unique to pathogenic mycobacteria. PGLs are found in several clinically relevant species, including various Mycobacterium tuberculosis strains, Mycobacterium leprae, and several nontuberculous mycobacterial pathogens, such as M. marinum. Multiple lines of investigation implicate PGLs in virulence, thus underscoring the relevance of a deep understanding of PGL biosynthesis. We report mutational and biochemical studies that interrogate the mechanism by which PGL biosynthetic intermediates (p-hydroxyphenylalkanoates) synthesized by the iterative polyketide synthase Pks15/1 are transferred to the noniterative polyketide synthase PpsA for acyl chain extension in M. marinum. Our findings support a model in which the transfer of the intermediates is dependent on a p-hydroxyphenylalkanoyl-AMP ligase (FadD29) acting as an intermediary between the iterative and the noniterative synthase systems. Our results also establish the p-hydroxyphenylalkanoate extension ability of PpsA, the first-acting enzyme of a multisubunit noniterative polyketide synthase system. Notably, this noniterative system is also loaded with fatty acids by a specific fatty acyl-AMP ligase (FadD26) for biosynthesis of phthiocerol dimycocerosates (PDIMs), which are nonglycosylated lipids structurally related to PGLs. To our knowledge, the partially overlapping PGL and PDIM biosynthetic pathways provide the first example of two distinct, pathway-dedicated acyl-AMP ligases loading the same type I polyketide synthase system with two alternate starter units to produce two structurally different families of metabolites. The studies reported here advance our understanding of the biosynthesis of an important group of mycobacterial glycolipids.

7,9-Diaryl-1,6,8-trioxaspiro[4.5]dec-3-en-2-ones: readily accessible and highly potent anticancer compounds.

7,9-Diaryl-1,6,8-trioxaspiro[4.5]dec-3-en-2-ones are a recently described group of spirocyclic butenolides that can be generated rapidly and as a single diastereomer through a cascade process between γ-hydroxybutenolides and aromatic aldehydes. The following outlines our findings that these spirocycles are potently cytotoxic and have a dramatic structure-function profile that provides excellent insight into the structural features required for this potency.

Biosynthesis of mycobacterial lipids by polyketide synthases and beyond.

Over a decade ago, the analysis of the complete sequence of the genome of the human pathogen Mycobacterium tuberculosis revealed an unexpectedly high number of open reading frames encoding proteins with homology to polyketide synthases (PKSs). PKSs form a large family of fascinating multifunctional enzymes best known for their involvement in the biosynthesis of hundreds of polyketide natural products with diverse biological activities. The surprising polyketide biosynthesis capacity of M. tuberculosis has been investigated since its initial inference from genome analysis. This investigation has been based on the genes found in M. tuberculosis or their orthologs found in other Mycobacterium species. Today, the majority of the PKS-encoding genes of M. tuberculosis have been linked to specific biosynthetic pathways required for the production of unique lipids or glycolipid conjugates that are critical for virulence and/or components of the extraordinarily complex mycobacterial cell envelope. This review provides a synopsis of the most relevant studies in the field and an overview of our current understanding of the involvement of PKSs and several other polyketide production pathway-associated proteins in critical biosynthetic pathways of M. tuberculosis and other mycobacteria. In addition, the most relevant studies on PKS-containing biosynthetic pathways leading to production of metabolites from mycobacteria other than M. tuberculosis are reviewed.

Pharmacokinetic and in vivo efficacy studies of the mycobactin biosynthesis inhibitor salicyl-AMS in mice.

Mycobactin biosynthesis in Mycobacterium tuberculosis facilitates iron acquisition, which is required for growth and virulence. The mycobactin biosynthesis inhibitor salicyl-AMS [5'-O-(N-salicylsulfamoyl)adenosine] inhibits M. tuberculosis growth in vitro under iron-limited conditions. Here, we conducted a single-dose pharmacokinetic study and a monotherapy study of salicyl-AMS with mice. Intraperitoneal injection yielded much better pharmacokinetic parameter values than oral administration did. Monotherapy of salicyl-AMS at 5.6 or 16.7 mg/kg significantly inhibited M. tuberculosis growth in the mouse lung, providing the first in vivo proof of concept for this novel antibacterial strategy.

Production of mycobacterial cell wall glycopeptidolipids requires a member of the MbtH-like protein family.

BACKGROUND: Glycopeptidolipids (GPLs) are among the major free glycolipid components of the outer membrane of several saprophytic and clinically-relevant Mycobacterium species. The architecture of GPLs is based on a constant tripeptide-amino alcohol core of nonribosomal peptide synthetase origin that is N-acylated with a 3-hydroxy/methoxy acyl chain synthesized by a polyketide synthase and further decorated with variable glycosylation patterns built from methylated and acetylated sugars. GPLs have been implicated in many aspects of mycobacterial biology, thus highlighting the significance of gaining an understanding of their biosynthesis. Our bioinformatics analysis revealed that every GPL biosynthetic gene cluster known to date contains a gene (referred herein to as gplH) encoding a member of the MbtH-like protein family. Herein, we sought to conclusively establish whether gplH was required for GPL production. RESULTS: Deletion of gplH, a gene clustered with nonribosomal peptide synthetase-encoding genes in the GPL biosynthetic gene cluster of Mycobacterium smegmatis, produced a GPL deficient mutant. Transformation of this mutant with a plasmid expressing gplH restored GPL production. Complementation was also achieved by plasmid-based constitutive expression of mbtH, a paralog of gplH found in the biosynthetic gene cluster for production of the siderophore mycobactin of M. smegmatis. Further characterization of the gplH mutant indicated that it also displayed atypical colony morphology, lack of sliding motility, altered capacity for biofilm formation, and increased drug susceptibility. CONCLUSIONS: Herein, we provide evidence formally establishing that gplH is essential for GPL production in M. smegmatis. Inactivation of gplH also leads to a pleiotropic phenotype likely to arise from alterations in the cell envelope due to the lack of GPLs. While genes encoding MbtH-like proteins have been shown to be needed for production of siderophores and antibiotics, our study presents the first case of one such gene proven to be required for production of a cell wall component. Furthermore, our results provide the first example of a mbtH-like gene with confirmed functional role in a member of the Mycobacterium genus. Altogether, our findings demonstrate a critical role of gplH in mycobacterial biology and advance our understanding of the genetic requirements for the biosynthesis of an important group of constituents of the mycobacterial outer membrane.

The mycobacterial acyltransferase PapA5 is required for biosynthesis of cell wall-associated phenolic glycolipids.

Phenolic glycolipids (PGLs) are non-covalently bound components of the outer membrane of many clinically relevant mycobacterial pathogens, and play important roles in pathogen biology. We report a mutational analysis that conclusively demonstrates that the conserved acyltransferase-encoding gene papA5 is essential for PGL production. In addition, we provide an in vitro acyltransferase activity analysis that establishes proof of principle for the competency of PapA5 to utilize diol-containing polyketide compounds of mycobacterial origin as acyl-acceptor substrates. Overall, the results reported herein are in line with a model in which PapA5 catalyses the acylation of diol-containing polyketides to form PGLs. These studies advance our understanding of the biosynthesis of an important group of mycobacterial glycolipids and suggest that PapA5 might be an attractive target for exploring the development of antivirulence drugs.

Chemical scaffolds with structural similarities to siderophores of nonribosomal peptide-polyketide origin as novel antimicrobials against Mycobacterium tuberculosis and Yersinia pestis.

Mycobacterium tuberculosis (Mtb) and Yersinia pestis (Yp) produce siderophores with scaffolds of nonribosomal peptide-polyketide origin. Compounds with structural similarities to these siderophores were synthesized and evaluated as antimicrobials against Mtb and Yp under iron-limiting conditions mimicking the iron scarcity these pathogens encounter in the host and under standard iron-rich conditions. Several new antimicrobials were identified, including some with increased potency in the iron-limiting condition. Our study illustrates the possibility of screening compound libraries in both iron-rich and iron-limiting conditions to identify antimicrobials that may selectively target iron scarcity-adapted bacteria and highlights the usefulness of building combinatorial libraries of compounds having scaffolds with structural similarities to siderophores to feed into antimicrobial screening programs.

Mutational and phylogenetic analyses of the mycobacterial mbt gene cluster.

The mycobactin siderophore system is present in many Mycobacterium species, including M. tuberculosis and other clinically relevant mycobacteria. This siderophore system is believed to be utilized by both pathogenic and nonpathogenic mycobacteria for iron acquisition in both in vivo and ex vivo iron-limiting environments, respectively. Several M. tuberculosis genes located in a so-called mbt gene cluster have been predicted to be required for the biosynthesis of the core scaffold of mycobactin based on sequence analysis. A systematic and controlled mutational analysis probing the hypothesized essential nature of each of these genes for mycobactin production has been lacking. The degree of conservation of mbt gene cluster orthologs remains to be investigated as well. In this study, we sought to conclusively establish whether each of nine mbt genes was required for mycobactin production and to examine the conservation of gene clusters orthologous to the M. tuberculosis mbt gene cluster in other bacteria. We report a systematic mutational analysis of the mbt gene cluster ortholog found in Mycobacterium smegmatis. This mutational analysis demonstrates that eight of the nine mbt genes investigated are essential for mycobactin production. Our genome mining and phylogenetic analyses reveal the presence of orthologous mbt gene clusters in several bacterial species. These gene clusters display significant organizational differences originating from an intricate evolutionary path that might have included horizontal gene transfers. Altogether, the findings reported herein advance our understanding of the genetic requirements for the biosynthesis of an important mycobacterial secondary metabolite with relevance to virulence.

Inactivation of tesA reduces cell wall lipid production and increases drug susceptibility in mycobacteria.

Phthiocerol dimycocerosates (PDIMs) and phenolic glycolipids (PGLs) are structurally related lipids noncovalently bound to the outer cell wall layer of Mycobacterium tuberculosis, Mycobacterium leprae, and several opportunistic mycobacterial human pathogens. PDIMs and PGLs are important effectors of virulence. Elucidation of the biosynthesis of these complex lipids will not only expand our understanding of mycobacterial cell wall biosynthesis, but it may also illuminate potential routes to novel therapeutics against mycobacterial infections. We report the construction of an in-frame deletion mutant of tesA (encoding a type II thioesterase) in the opportunistic human pathogen Mycobacterium marinum and the characterization of this mutant and its corresponding complemented strain control in terms of PDIM and PGL production. The growth and antibiotic susceptibility of these strains were also probed and compared with the parental wild-type strain. We show that deletion of tesA leads to a mutant that produces only traces of PDIMs and PGLs, has a slight growth yield increase and displays a substantial hypersusceptibility to several antibiotics. We also provide a robust model for the three-dimensional structure of M. marinum TesA (TesAmm) and demonstrate that a Ser-to-Ala substitution in the predicted catalytic Ser of TesAmm renders a mutant that recapitulates the phenotype of the tesA deletion mutant. Overall, our studies demonstrate a critical role for tesA in mycobacterial biology, advance our understanding of the biosynthesis of an important group of polyketide synthase-derived mycobacterial lipids, and suggest that drugs aimed at blocking PDIM and/or PGL production might synergize with antibiotic therapy in the control of mycobacterial infections.

Cooperation between a coenzyme A-independent stand-alone initiation module and an iterative type I polyketide synthase during synthesis of mycobacterial phenolic glycolipids.

Several Mycobacterium tuberculosis strains, Mycobacterium leprae, and other mycobacterial pathogens produce a group of small-molecule virulence factors called phenolic glycolipids (PGLs). PGLs play key roles in pathogenicity and host-pathogen interaction. Thus, elucidation of the PGL biosynthetic pathway will not only expand our understanding of natural product biosynthesis, but may also illuminate routes to novel therapeutics to afford alternative lines of defense against mycobacterial infections. In this study, we report an investigation of the enzymatic requirements for the production of long-chain p-hydroxyphenylalkanoate intermediates of PGL biosynthesis. We demonstrate a functional cooperation between a coenzyme A-independent stand-alone didomain initiation module (FadD22) and a 6-domain reducing iterative type I polyketide synthase (Pks15/1) for production of p-hydroxyphenylalkanoate intermediates in in vitro and in vivo FadD22-Pks15/1 reconstituted systems. Our results suggest that Pks15/1 is an iterative type I polyketide synthase with a relaxed control of catalytic cycle iterations, a mechanistic property that explains the origin of a characteristic alkyl chain length variability seen in mycobacterial PGLs. The FadD22-Pks15/1 reconstituted systems lay an initial foundation for future efforts to unveil the mechanism of iterative catalysis control by which the structures of the final products of Pks15/1 are defined, and to scrutinize the functional partnerships of the FadD22-Pks15/1 system with downstream enzymes of the PGL biosynthetic pathway.

Influence of the cystic fibrosis transmembrane conductance regulator on expression of lipid metabolism-related genes in dendritic cells.

BACKGROUND: Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Infections of the respiratory tract are a hallmark in CF. The host immune responses in CF are not adequate to eradicate pathogens, such as P. aeruginosa. Dendritic cells (DC) are crucial in initiation and regulation of immune responses. Changes in DC function could contribute to abnormal immune responses on multiple levels. The role of DC in CF lung disease remains unknown. METHODS: This study investigated the expression of CFTR gene in bone marrow-derived DC. We compared the differentiation and maturation profile of DC from CF and wild type (WT) mice. We analyzed the gene expression levels in DC from naive CF and WT mice or following P. aeruginosa infection. RESULTS: CFTR is expressed in DC with lower level compared to lung tissue. DC from CF mice showed a delayed in the early phase of differentiation. Gene expression analysis in DC generated from naive CF and WT mice revealed decreased expression of Caveolin-1 (Cav1), a membrane lipid raft protein, in the CF DC compared to WT DC. Consistently, protein and activity levels of the sterol regulatory element binding protein (SREBP), a negative regulator of Cav1 expression, were increased in CF DC. Following exposure to P. aeruginosa, expression of 3beta-hydroxysterol-Delta7 reductase (Dhcr7) and stearoyl-CoA desaturase 2 (Scd2), two enzymes involved in the lipid metabolism that are also regulated by SREBP, was less decreased in the CF DC compared to WT DC. CONCLUSION: These results suggest that CFTR dysfunction in DC affects factors involved in membrane structure and lipid-metabolism, which may contribute to the abnormal inflammatory and immune response characteristic of CF.

Small molecules with structural similarities to siderophores as novel antimicrobials against Mycobacterium tuberculosis and Yersinia pestis.

Drugs inhibiting the iron scarcity-induced, siderophore-mediated iron-scavenging systems of Mycobacterium tuberculosis (Mtb) and Yersinia pestis (Yp) may provide new therapeutic lines of defense. Compounds with structural similarities to siderophores were synthesized and evaluated as antimicrobials against Mtb and Yp under iron-limiting conditions, which mimic the iron scarcity these pathogens encounter and must adapt to in the host, and under standard iron-rich conditions for comparison. New antimicrobials were identified, some of which warrant exploration as initial leads against potentially novel targets and small-molecule tools to assist in the elucidation of targets specific to iron-scarcity adapted Mtb and Yp.