Overcome low levels of detection limit and choice of antibody affects detection of lipoarabinomannan in pediatric tuberculosis.

The World Health Organization (WHO) emphasizes that tuberculosis (TB) in children and adolescents is often overlooked by healthcare providers and difficult to diagnose. As childhood TB cases rise, finding a diagnostic high in sensitivity and specificity is critical. In this study 91 urine samples from children aged 1-10 years were analyzed for tuberculostearic acid (TBSA) by gas chromatography/mass spectrometry (GC/MS) and capture ELISA (C-ELISA). In C-ELISA the CS35/A194-01 antibody performed very poorly with both curve-based and model-based cutoffs. The area under the ROC curve (AUC) of the CS35 OD450 values was only 0.60. Replacing the capture antibody with BJ76 gave a better performance in both sensitivity and specificity (AUC = 0.95). When these samples were analyzed by GC/MS, 41 classified as 'probable/possible' for TB were distinctly TBSA positive with ten samples having <3 ng/mL LAM. However, from the 50 samples with 'unlikely' TB classification, 36 were negative but 7 had >3 ng/mL and were designated as LAM positive. This experimental assay assessment study signifies that i) the antibody pair CS35/A194-01 that has been successful for adult active TB diagnosis is not adequate when LAM level is low as in pediatric TB; ii) no one mAb appears to recognize all TB-specific LAM epitopes.

Simple manipulation of enzyme-linked immunosorbent assay (ELISA) using an automated microfluidic interface.

Among lateral flow immunoassay (LFIA) platforms, enzyme-based LFIAs provide signal amplification to improve sensitivity. However, most enzyme-based LFIAs require multiple timed steps, complicating their utility in point-of-care testing (POCT). Here, we report a microfluidic interface for LFIAs that automates sample, buffer, and reagent addition, greatly simplifying operation while achieving the high analytical stringency associated with more complex assays. The microfluidic interface also maintains the low cost and small footprint of standard LFIAs. The platform is fabricated from a combination of polyester film, double-sided adhesive tape, and nitrocellulose, and fits in the palm of your hand. All reagents are dried on the nitrocellulose to facilitate sequential reagent delivery, and the sample is used as the wash buffer to minimize steps. After the sample addition, a user simply waits 15 min for a colorimetric result. This manuscript discusses the development and optimization of the channel geometry to achieve a simple step enzyme amplified immunoassay. As a proof-of-concept target, we selected lipoarabinomannan (LAM), a WHO identified urinary biomarker of active tuberculosis, to demonstrate the device feasibility and reliability. The results revealed that the device successfully detected LAM in phosphate buffer (PBS) as well as spiked urine samples within 15 min after sample loading. The minimum concentration of color change was achieved at 25 ng mL-1.

Monoclonal antibodies from humans with Mycobacterium tuberculosis exposure or latent infection recognize distinct arabinomannan epitopes.

The surface polysacharide arabinomannan (AM) and related glycolipid lipoarabinomannan (LAM) play critical roles in tuberculosis pathogenesis. Human antibody responses to AM/LAM are heterogenous and knowledge of reactivity to specific glycan epitopes at the monoclonal level is limited, especially in individuals who can control M. tuberculosis infection. We generated human IgG mAbs to AM/LAM from B cells of two asymptomatic individuals exposed to or latently infected with M. tuberculosis. Here, we show that two of these mAbs have high affinity to AM/LAM, are non-competing, and recognize different glycan epitopes distinct from other anti-AM/LAM mAbs reported. Both mAbs recognize virulent M. tuberculosis and nontuberculous mycobacteria with marked differences, can be used for the detection of urinary LAM, and can detect M. tuberculosis and LAM in infected lungs. These mAbs enhance our understanding of the spectrum of antibodies to AM/LAM epitopes in humans and are valuable for tuberculosis diagnostic and research applications.

Structural implications of lipoarabinomannan glycans from global clinical isolates in diagnosis of Mycobacterium tuberculosis infection.

In Mycobacterium tuberculosis (Mtb), surface-exposed Lipoarabinomannan (LAM) is a key determinant of immunogenicity, yet its intrinsic heterogeneity confounds typical structure-function analysis. Recently, LAM gained a strong foothold as a validated marker for active tuberculosis (TB) infection and has shown great potential in new diagnostic efforts. However, no efforts have yet been made to model or evaluate the impact of mixed polyclonal Mtb infections (infection with multiple strains) on TB diagnostic procedures other than antibiotic susceptibility testing. Here, we selected three TB clinical isolates (HN878, EAI, and IO) and purified LAM from these strains to present an integrated analytical approach of one-dimensional and two-dimensional Nuclear Magnetic Resonance (NMR) spectroscopy, as well as enzymatic digestion and site-specific mass spectrometry (MS) to probe LAM structure and behavior at multiple levels. Overall, we found that the glycan was similar in all LAM preparations, albeit with subtle variations. Succinates, lactates, hydroxybutyrate, acetate, and the hallmark of Mtb LAM-methylthioxylose (MTX), adorned the nonreducing terminal arabinan of these LAM species. Newly identified acetoxy/hydroxybutyrate was present only in LAM from EAI and IO Mtb strains. Notably, detailed LC/MS-MS unambiguously showed that all acyl modifications and the lactyl ether in LAM are at the 3-OH position of the 2-linked arabinofuranose adjacent to the terminal ß-arabinofuranose. Finally, after sequential enzymatic deglycosylation of LAM, the residual glycan that has ∼50% of α-arabinofuranose -(1→5) linked did not bind to monoclonal antibody CS35. These data clearly indicate the importance of the arabinan termini arrangements for the antigenicity of LAM.

Immobilization of Proteinase K for urine pretreatment to improve diagnostic accuracy of active tuberculosis.

The World Health Organization (WHO) calls for the development of a rapid, biomarker-based, non-sputum test capable of detecting all forms of tuberculosis (TB) at the point-of-care to enable immediate treatment initiation. Lipoarabinomannan (LAM) is the only WHO-endorsed TB biomarker that can be detected in urine, an easily collected sample matrix. For obtaining optimal sensitivity, we and others have shown that some form of sample pretreatment is necessary to remove background from patient urine samples. A number of systems are paper-based often destined for resource limited settings. Our current work presents incorporation of one such sample pretreatment, proteinase K (ProK) immobilized on paper (IPK) and test its performance in comparison to standard proteinase K (SPK) treatment that involves addition and deactivation at high temperature prior to performing a capture ELISA. Herein, a simple and economical method was developed for using ProK immobilized strips to pretreat urine samples. Simplification and cost reduction of the proposed pretreatment strip were achieved by using Whatman no.1 paper and by minimizing the concentration of ProK (an expensive but necessary reagent) used to pretreat the clinical samples prior to ELISA. To test the applicability of IPK, capture ELISA was carried out on either LAM-spiked urine or the clinical samples after pretreatment with ProK at 400 µg/mL for 30 minutes at room temperature. The optimal conditions and stability of the IPK were tested and validation was performed on a set of 25 previously analyzed archived clinical urine samples with known TB and HIV status. The results of IPK and SPK treated samples were in agreement showing that the urine LAM test currently under development has the potential to reach adult and pediatric patients regardless of HIV status or site of infection, and to facilitate global TB control to improve assay performance and ultimately treatment outcomes.

Culturing Mycobacteria.

Building upon the foundational research of Robert Koch, who demonstrated the ability to grow Mycobacterium tuberculosis for the first time in 1882 using media made of coagulated bovine serum, microbiologists have continued to develop new and more efficient ways to grow mycobacteria. Presently, all known mycobacterial species can be grown in the laboratory using either axenic culture techniques or in vivo passage in laboratory animals. This chapter provides conventional protocols to grow mycobacteria for diagnostic purposes directly from clinical specimens, as well as in research laboratories for scientific purposes. Detailed protocols used for production of M. tuberculosis in large scale (under normoxic and hypoxic conditions) in bioreactors and for production of obligate intracellular pathogens such as Mycobacterium leprae and "Mycobacterium lepromatosis" using athymic nude mice and armadillos are provided.

Urine lipoarabinomannan in HIV uninfected, smear negative, symptomatic TB patients: effective sample pretreatment for a sensitive immunoassay and mass spectrometry.

Our study sought to determine whether urine lipoarabinomannan (LAM) could be validated in a sample cohort that consisted mainly of HIV uninfected individuals that presented with tuberculosis symptoms. We evaluated two tests developed in our laboratory, and used them on clinical samples from Lima, Peru where incidence of HIV is low. ELISA analysis was performed on 160 samples (from 140 adult culture-confirmed TB cases and 20 symptomatic TB-negative child controls) using 100 µL of urine after pretreatment with Proteinase K. Two different mouse monoclonal antibodies-CS35 and CHCS9-08 were used individually for capture of urine LAM. Among cases, optical density (OD450) values had a positive association with higher bacillary loads. The 20 controls had negative values (below the limit of detection). The assay correctly identified all samples (97-100% accuracy confidence interval). For an alternate validation of the ELISA results, we analyzed all 160 urine samples using an antibody independent chemoanalytical approach. Samples were called positive only when LAM surrogates-tuberculostearic acid (TBSA) and D-arabinose (D-ara)-were found to be present in similar amounts. All TB cases, including the 40 with a negative sputum smear had LAM in detectable quantities in urine. None of the controls had detectable amounts of LAM. Our study shows that urinary LAM detection is feasible in HIV uninfected, smear negative TB patients.

Urine lipoarabinomannan as a marker for low-risk of NTM infection in the CF airway.

BACKGROUND: Individuals with Cystic fibrosis (CF) are the most vulnerable population for pulmonary infection with nontuberculous mycobacteria (NTM). Screening, diagnosis, and assessment of treatment response currently depend on traditional culture techniques, but sputum analysis for NTM in CF is challenging, and associated with a low sensitivity. The cell wall lipoarabinomannan (LAM), a lipoglycan found in all mycobacterial species, and has been validated as a biomarker in urine for active Mycobacterium tuberculosis infection. METHODS: Urine from a CF cohort (n = 44) well-characterized for NTM infection status by airway cultures was analyzed for LAM by gas chromatography/mass spectrometry. All subjects with positive sputum cultures for NTM had varying amounts of LAM in their urine. No LAM was detected in subjects who never had a positive culture (14/45). One individual initially classified as NTM sputum negative subsequently developed NTM disease 657 days after the initial urine LAM testing. Repeat urine LAM testing turned positive, correlating to her positive NTM status. Subjects infected with subspecies of M. abscessus had greater LAM quantities than those infected with M. avium complex (MAC). There was no correlation with disease activity or treatment status and LAM quantity. A TB Capture ELISA using anti-LAM antibodies demonstrated very poor sensitivity in identifying individuals with positive NTM sputum cultures. CONCLUSION: These findings support the conclusion that urine LAM related to NTM infection may be a useful screening test to determine patients at low risk for having a positive NTM sputum culture, as part of a lifetime screening strategy in the CF population.

Detection of lipoarabinomannan in urine and serum of HIV-positive and HIV-negative TB suspects using an improved capture-enzyme linked immuno absorbent assay and gas chromatography/mass spectrometry.

TB diagnosis and treatment monitoring in resource limited regions rely heavily on serial sputum smear microscopy and bacterial culture. These microbiological methods are time-consuming, expensive and lack adequate sensitivity. The WHO states that improved TB diagnosis and treatment is imperative to achieve an end to the TB epidemic by 2030. Commercially available lipoarabinomannan (LAM) detection tools perform at low sensitivity that are highly dependent on the underlying immunological status of the patient; those with advanced HIV infection perform well. In this study, we have applied two novel strategies towards the sensitive diagnosis of TB infection based on LAM: Capture ELISA to detect LAM in paired urine and serum samples using murine and human monoclonal antibodies, essentially relying on LAM as an 'immuno-marker'; and, secondly, detection of α-d-arabinofuranose and tuberculostearic acid (TBSA)- 'chemical-markers' unique to mycobacterial cell wall polysaccharides/lipoglycans by our recently developed gas chromatography/mass spectrometry (GC/MS) method. Blinded urine specimens, with microbiologically confirmed active pulmonary TB or non TB (HIV+/HIV-) were tested by the aforementioned assays. LAM in patient urine was detected in a concentration range of 3-28 ng/mL based on GC/MS detection of the two LAM-surrogates, d-arabinose and tuberculostearic acid (TBSA) correctly classifying TB status with sensitivity > 99% and specificity = 84%. The ELISA assay had high sensitivity (98%) and specificity (92%) and the results were in agreement with GC/MS analysis. Both tests performed well in their present form particularly for HIV-negative/TB-positive urine samples. Among the HIV+/TB+ samples, 52% were found to have >10 ng/mL urinary LAM. The detected amounts of LAM present in the urine samples also appears to be associated with the gradation of the sputum smear, linking elevated LAM levels with higher mycobacterial burden (odds ratio = 1.08-1.43; p = 0.002). In this small set, ELISA was also applied to parallel serum samples confirming that serum could be an additional reservoir for developing a LAM-based immunoassay for diagnosis of TB.

Estimation of D-Arabinose by Gas Chromatography/Mass Spectrometry as Surrogate for Mycobacterial Lipoarabinomannan in Human Urine.

Globally, tuberculosis is slowly declining each year and it is estimated that 37 million lives were saved between 2000 and 2013 through effective diagnosis and treatment. Currently, diagnosis relies on demonstration of the bacteria, Mycobacterium tuberculosis (Mtb), in clinical specimens by serial sputum microscopy, culture and molecular testing. Commercial immunoassay lateral flow kits developed to detect Mtb lipoglycan lipoarabinomannan (LAM) in urine as a marker of active TB exhibit poor sensitivity, especially in immunocompetent individuals, perhaps due to low abundance of the analyte. Our present study was designed to develop methods to validate the presence of LAM in a quantitative fashion in human urine samples obtained from culture-confirmed TB patients. Herein we describe, a consolidated approach for isolating LAM from the urine and quantifying D-arabinose as a proxy for LAM, using Gas Chromatography/Mass Spectrometry. 298 urine samples obtained from a repository were rigorously analyzed and shown to contain varying amounts of LAM-equivalent ranging between ~10-40 ng/mL. To further substantiate that D-arabinose detected in the samples originated from LAM, tuberculostearic acid, the unique 10-methyloctadecanoic acid present at the phosphatidylinositol end of LAM was also analyzed in a set of samples and found to be present confirming that the D-arabinose was indeed derived from LAM. Among the 144 samples from culture-negative TB suspects, 30 showed presence of D-arabinose suggesting another source of the analyte, such as disseminated TB or from non-tuberculosis mycobacterium. Our work validates that LAM is present in the urine samples of culture-positive patients in small but readily detectable amounts. The study further substantiates LAM in urine as a powerful biomarker for active tuberculosis.

Metabolomic signatures in guinea pigs infected with epidemic-associated W-Beijing strains of Mycobacterium tuberculosis.

With the understanding that the laboratory propagated strain of Mycobacterium tuberculosis H37Rv is of modest virulence and is drug susceptible, in the present study, we performed a nuclear magnetic resonance-based metabolomic analysis of lung tissues and serum obtained from guinea pigs infected by low dose aerosol exposure to clinical isolates of Mycobacterium tuberculosis. High Resolution Magic Angle Spinning NMR coupled with multivariate statistical analysis of 159 lung tissues obtained from multiple locations of age-matched naïve and 30 and 60 days of infected guinea pig lungs revealed a wide dispersal of metabolic patterns, but within these, distinct clusters of signatures could be seen that differentiated between naive control and infected animals. Several metabolites were identified that changed in concert with the progression of each infection. Major metabolites that could be interpreted as indicating host glutaminolysis were consistent with activated host immune cells encountering increasingly hypoxic conditions in the necrotic lung lesions. Moreover, glutathione levels were constantly elevated, probably in response to oxygen radical production in these lesions. Additional distinct signatures were also seen in infected serum, with altered levels of several metabolites. Multivariate statistical analysis clearly differentiated the infected from the uninfected sera; in addition, Receiver Operator Characteristic curve generated with principal component 1 scores showed an area under the curve of 0.908. These data raise optimism that discrete metabolomic signatures can be defined that can predict the progression of the tuberculosis disease process, and form the basis of an innovative and rapid diagnostic process.

Metabolic profiling of lung granuloma in Mycobacterium tuberculosis infected guinea pigs: ex vivo 1H magic angle spinning NMR studies.

A crucial and distinctive feature of tuberculosis infection is that Mycobacterium tuberculosis (Mtb) resides in granulomatous lesion at various stages of disease development and necrosis, an aspect that is little understood. We used a novel approach, applying high resolution magic angle spinning nuclear magnetic resonance spectroscopy (HRMAS NMR) directly to infected tissues, allowing us to study the development of tuberculosis granulomas in guinea pigs in an untargeted manner. Significant up-regulation of lactate, alanine, acetate, glutamate, oxidized and the reduced form of glutathione, aspartate, creatine, phosphocholine, glycerophosphocholine, betaine, trimethylamine N-oxide, myo-inositol, scyllo-inositol, and dihydroxyacetone was clearly visualized and was identified as the infection progressed. Concomitantly, phosphatidylcholine was down-regulated. Principal component analysis of NMR data revealed clear group separation between infected and uninfected tissues. These metabolites are suggestive of utilization of alternate energy sources by the infiltrating cells that generate much of the metabolites in the increasingly necrotic and hypoxic developing granuloma through the glycolytic, pentose phosphate, and tricarboxylic acid pathways. The most relevant changes seen are, surprisingly, very similar to metabolic changes seen in cancer during tumor development.

Development of a plate-based scintillation proximity assay for the mycobacterial AftB enzyme involved in cell wall arabinan biosynthesis.

A number of mycobacterial arabinosyltransferases, such as the Emb proteins, AftA, AftB, AftC, and AftD have been characterized and implicated to be involved in the cell wall arabinan assembly. These arabinosyltransferases are essential for the viability of the organism and are logically valid targets for developing new anti-tuberculosis agents. For instance, Ethambutol, a first line anti-tuberculosis drug, targets the Emb proteins involved in the formation of the arabinan of cell wall arabinogalactan. Among these arabinosyltransferases, the terminal ß-(1→2) arabinosyltransferase activity has been associated with AftB. The predicted topology of AftB in Mycobacterium tuberculosis has 10 N terminal transmembrane domains and a C terminal hydrophilic domain similar to the Emb proteins. It has a conserved GT-C motif and is difficult to express. In a cell free assay, synthetic disaccharide, α-D-Araf-(1→5)-α-D-Araf-octyl, has been used as a substrate to explore the function of AftB. In our work, the disaccharide was synthesized in its pentenylated and biotinylated form, and the enzymatic product formed was identified as the ß-(1→2) arabinofuranose adduct. When synthetic tri- and tetra-saccharides were used as substrates, a mixture of products containing both ß-(1→2) and α-(1→5) linkages were formed. Therefore, the biotinylated disaccharide was selected to develop a scintillation proximity assay.

Rapid screening of inhibitors of Mycobacterium tuberculosis growth using tetrazolium salts.

With the increased need for novel antimicrobials to improve the existing treatment for tuberculosis, to combat multidrug-resistant tuberculosis, and to address the presence of latent bacilli in a large population throughout the world, which can reactivate and cause active disease, there is a need for rapid, low-cost, high-throughput assays for screening new drug candidates. A microplate-based Alamar blue assay meets these requirements. In addition to the identification of the antimicrobial activities of compounds, determination of their toxicities is important. The high costs involved in testing compounds in whole animal models has led to the development of in vitro cytotoxicity assays using human and animal cell lines. Microplate-based Alamar blue and cytotoxicity assays have been applied to search for novel antimicrobials to treat tuberculosis. These methods are described in detail herein.

The critical role of embC in Mycobacterium tuberculosis.

Arabinan polymers are major components of the cell wall in Mycobacterium tuberculosis and are involved in maintaining its structure, as well as playing a role in host-pathogen interactions. In particular, lipoarabinomannan (LAM) has multiple immunomodulatory effects. In the nonpathogenic species Mycobacterium smegmatis, EmbC has been identified as a key arabinosyltransferase involved in the incorporation of arabinose into LAM, and an embC mutant is viable but lacks LAM. In contrast, we demonstrate here that in M. tuberculosis, embC is an essential gene under normal growth conditions, suggesting a more crucial role for LAM in the pathogenic mycobacteria. M. tuberculosis EmbC has an activity similar to that of M. smegmatis EmbC, since we were able to complement an embC mutant of M. smegmatis with embC(Mtb), confirming that it encodes a functional arabinosyltransferase. In addition, we observed that the size of LAM produced in M. smegmatis was dependent on the level of expression of embC(Mtb). Northern analysis revealed that embC is expressed as part of a polycistronic message encompassing embC and three upstream genes. The promoter region for this transcript was identified and found to be up-regulated in stationary phase but down-regulated during hypoxia-induced nonreplicating persistence. In conclusion, we have identified one of the key genes involved in LAM biosynthesis in M. tuberculosis and confirmed its essential role in this species.

EmbA is an essential arabinosyltransferase in Mycobacterium tuberculosis.

The Emb proteins (EmbA, EmbB, EmbC) are mycobacterial arabinosyltransferases involved in the biogenesis of the mycobacterial cell wall. EmbA and EmbB are predicted to work in unison as a heterodimer. EmbA and EmbB are involved in the formation of the crucial terminal hexaarabinoside motif [Arabeta(1-->2)Araalpha(1-->5)] [Arabeta(1-->2)Araalpha(1-->3)]Araalpha(1-->5)Araalpha1-->(Ara(6)) in the cell wall polysaccharide arabinogalactan. Studies conducted in Mycobacterium smegmatis revealed that mutants with disruptions in embA or embB are viable, although the growth rate was affected. In contrast, we demonstrate here that embA is an essential gene in Mycobacterium tuberculosis, since a deletion of the chromosomal gene could only be achieved when a second functional copy was provided on an integrated vector. Complementation of an embA mutant of M. smegmatis by M. tuberculosis embA confirmed that it encodes a functional arabinosyltransferase. We identified a promoter for M. tuberculosis embA located immediately upstream of the gene, indicating that it is expressed independently from the upstream gene, embC. Promoter activity from P(embA)((Mtb)) was sevenfold lower when assayed in M. smegmatis compared to M. tuberculosis, indicating that the latter is not a good host for genetic analysis of M. tuberculosis embA expression. P(embA)((Mtb)) activity remained constant throughout growth phases and after stress treatment, although it was reduced during hypoxia-induced non-replicating persistence. Ethambutol exposure had no effect on P(embA)((Mtb)) activity. These data demonstrate that M. tuberculosis embA encodes a functional arabinosyltransferase which is constitutively expressed and plays a critical role in M. tuberculosis.

Genome differences between Treponema pallidum subsp. pallidum strain Nichols and T. paraluiscuniculi strain Cuniculi A.

The genome of Treponema paraluiscuniculi strain Cuniculi A was compared to the genome of the syphilis spirochete Treponema pallidum subsp. pallidum strain Nichols using DNA microarray hybridization, whole-genome fingerprinting, and DNA sequencing. A DNA microarray of T. pallidum subsp. pallidum Nichols containing all 1,039 predicted open reading frame PCR products was used to identify deletions and major sequence changes in the Cuniculi A genome. Using these approaches, deletions, insertions, and prominent sequence changes were found in 38 gene homologs and six intergenic regions of the Cuniculi A genome when it was compared to the genome of T. pallidum subsp. pallidum Nichols. Most of the observed differences were localized in tpr loci and the vicinity of these loci. In addition, 14 other genes were found to contain frameshift mutations resulting in major changes in protein sequences. Analysis of restriction target sites representing 0.34% of the total genome length and DNA sequencing of three PCR products (0.46% of the total genome length) amplified from Cuniculi A chromosomal regions and comparison to the Nichols genome revealed a sequence similarity of 98.6 to 99.3%. These results are consistent with a close genetic relationship among the T. pallidum strains and subspecies and a strong, but relatively divergent connection between the human and rabbit pathogens.

Targeting fatty acid biosynthesis for the development of novel chemotherapeutics against Mycobacterium tuberculosis: evaluation of A-ring-modified diphenyl ethers as high-affinity InhA inhibitors.

Structure-based design was used to develop a focused library of A-ring-modified diphenyl ether InhA inhibitors. From this library of analogs, two high-affinity alkyl-substituted diphenyl ethers, 6PP and 8PP, were selected for advanced study into their in vitro activity against Mycobacterium tuberculosis clinical isolates, their in vivo properties, and their signature response mode of action. 6PP and 8PP demonstrated enhanced activity against whole bacteria and showed activity in a rapid macrophage model of infection. In addition, transcriptional profiling revealed that the A-ring modifications of 6PP and 8PP increased the specificity of each analog for InhA. Both analogs had substantially longer half-lives in serum than did the parent compound, exhibited a fivefold reduction in cytotoxicity compared to the parent compound, and were well tolerated when administered orally at 300 mg/kg of body weight in animal models. Thus, the A-ring modifications increased the affinity and whole-cell specificity of the compounds for InhA and increased their bioavailability. The next step in optimization of the pharmacophore for preclinical evaluation is modification of the B ring to increase the bioavailability to that required for oral delivery.

Characterization of a specific arabinosyltransferase activity involved in mycobacterial arabinan biosynthesis.

Mycobacterium smegmatis strains that contain inactivated EmbA or EmbB proteins are unable to synthesize terminal Arabeta1-->2Araalpha1-->5(Arabeta1-->2Araalpha1-->3)Araalpha1-->5Araalpha1-->(Ara(6)) motif in the cell wall polysaccharide arabinogalactan. Instead, the mutants contain a linear Arabeta1-->2Araalpha1-->5Araalpha1-->5Araalpha1-->(Ara(4)) motif, suggesting that these proteins are involved in the synthesis or transfer of the disaccharide Arabeta1-->2Araalpha1--> to an internal 5-linked Ara. Therefore, we synthesized a linear Arabeta1-->2Araalpha1-->5Araalpha1-->5Araalpha1-->5Araalpha1--> with an octyl aglycon as an arabinosyl acceptor in cell-free assays. A facile assay was developed using the chemically synthesized glycan, membrane, and particulate cell wall as the enzyme source, and 5-phosphoribose diphosphate pR[(14)C]pp as the arabinose donor. The results unequivocally show that two arabinofuranosyl residues were added at the tertiary -->5Araalpha1--> of the synthetic glycan. This activity was undetectable in strains of M. smegmatis where embB or embA had been genetically disrupted. Normal activity could be restored only in the presence of both EmbA and EmbB proteins.

Genetic basis for the synthesis of the immunomodulatory mannose caps of lipoarabinomannan in Mycobacterium tuberculosis.

Lipoarabinomannan (LAM) is a high molecular weight, heterogenous lipoglycan present in abundant quantities in Mycobacterium tuberculosis and many other actinomycetes. In M. tuberculosis, the non-reducing arabinan termini of the LAM are capped with alpha1-->2 mannose residues; in some other species, the arabinan of LAM is not capped or is capped with inositol phosphate. The nature and extent of this capping plays an important role in disease pathogenesis. MT1671 in M. tuberculosis CDC1551 was identified as a glycosyltransferase that could be involved in LAM capping. To determine the function of this protein a mutant strain of M. tuberculosis CDC1551 was studied, in which MT1671 was disrupted by transposition. SDS-PAGE analysis showed that the LAM of the mutant strain migrated more rapidly than that of the wild type and did not react with concanavalin A as did wild-type LAM. Structural analysis using NMR, gas chromatography/mass spectrometry, endoarabinanase digestion, Dionex high pH anion exchange chromatography, and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry demonstrated that the LAM of the mutant strain was devoid of mannose capping. Since an ortholog of MT1671 is not present in Mycobacterium smegmatis mc(2)155, a recombinant strain was constructed that expressed this protein. Analysis revealed that the LAM of the recombinant strain was larger than that of the wild type, had gained concanavalin A reactivity, and that the arabinan termini were capped with a single mannose residue. Thus, MT1671 is the mannosyltransferase involved in deposition of the first of the mannose residues on the non-reducing arabinan termini and the basis of much of the interaction between the tubercle bacillus and the host cell.