Isolation and characterization of arabinose mycolate from firmly bound lipids of mycobacteria

The synthesis of mycobacterial dimycoloyl diarabinoglycerol based on defined synthetic mycolic acids

Complex mixtures of natural dimycoloyl diarabinoglycerols isolated from mycobacteria have been shown to be both potent immune signalling agents and potentially valuable antigens in the serodiagnosis of mycobacterial infections. We now report the highly stereocontrolled synthesis of diacyl l-glycerol-(1'→1)-β-d-arabinofuranosyl-α-d-arabinofuranosides based on simple fatty acids and single defined synthetic mycolic acids. NMR analysis confirmed that the synthetic core was identical to that in natural mixtures.

N-glycolylated peptidoglycan contributes to the immunogenicity but not pathogenicity of Mycobacterium tuberculosis

Mycobacteria produce an unusual, glycolylated form of muramyl dipeptide (MDP) that is more potent and efficacious at inducing NOD2-mediated host responses. We tested the importance of this modified form of MDP in Mycobacterium tuberculosis by disrupting the gene, namH, responsible for this modification. In vitro, the namH mutant did not produce N-glycolylated muropeptides, but there was no alteration in colony morphology, growth kinetics, cellular morphology, or mycolic acid profile. Ex vivo, the namH mutant survived and replicated normally in murine and human macrophages, yet induced diminished production of tumor necrosis factor α. In vivo, namH disruption did not affect the bacterial burden during infection of C57BL/6 mice or cellular recruitment to the lungs but modestly prolonged survival after infection in Rag1(-/-) mice. These results indicate that the modified MDP is an important contributor to the unusual immunogenicity of mycobacteria but has a limited role in the pathogenesis of M. tuberculosis infection.

Polysaccharides of Mycobacterium bovis Ushi 10, Mycobacterium smegmatis, Mycobacterium phlei, and Atypical Mycobacterium P1

Four kinds of polysaccharides, glucan, mannan, arabinomannan, and arabinogalactan, were purified from the defatted cells of four strains of mycobacteria. By the chemical and immunological analyses, we concluded that arabinomannan and arabinogalactan are common serologically active polysaccharides in mycobacteria.

Design, synthesis and biological evaluation of sugar-derived esters, alpha-ketoesters and alpha-ketoamides as inhibitors for Mycobacterium tuberculosis antigen 85C

Peptide-based 1,2-dicarbonyl compounds have emerged as potent inhibitors for serine proteases. Herein, we have designed and synthesized d-arabinose and d-trehalose-based esters, alpha-ketoesters and alpha-ketoamides, and evaluated their inhibitory activity against Mycobacterium tuberculosis (Mtb) antigen 85C (ag85C), an acyltransferase in the serine hydrolase superfamily. In addition the compounds were evaluated for the ability to inhibit the growth of Mycobacterium smegmatis ATCC 14 468, a non-pathogenic surrogate for Mtb. Among the synthetic analogs evaluated only the methyl ester derived from d-arabinose was found to inhibit the acyltransferase activity of ag85C (IC(50) = 25 mM). Based on this weak inhibitory activity it was not surprising that none of the compounds inhibits the growth of M. smegmatis. In spite of the weak inhibitory activity of , X-ray crystallography on crystals of ag85C soaked with suggested the formation of a covalent ester adduct between and the Ser124 side chain hydroxyl moiety found within the catalytic site of ag85C; however, some of the active site electron density appears to result from bound glycerol. The lack of activity associated with the alpha-ketoester and alpha-ketoamide derivatives of d-trehalose may be the result of intramolecular cyclization of the alpha-keto moiety with the nearby C-4/4' hydroxyls leading to the formation of stable bicyclo-ester and amide derivatives.

Antigen 85C-mediated acyl-transfer between synthetic acyl donors and fragments of the arabinan

Antigen 85 (ag85) is a complex of acyltransferases (ag85A-C) known to play a role in the mycolation of the D-arabino-D-galactan (AG) component of the mycobacterial cell wall. In order to better understand the chemistry and substrate specificity of ag85, a trehalose monomycolate mimic p-nitrophenyl 6-O-octanoyl-beta-D-glucopyranoside (1) containing an octanoyl moiety in lieu of a mycolyl moiety was synthesized as an acyl donor. Arabinofuranoside acceptors, methyl alpha-D-arabinofuranoside (2), methyl beta-D-arabinofuranoside (3), and methyl 2-O-beta-D-arabinofuranosyl-alpha-D-arabinofuranoside (9) were synthesized to mimic the terminal saccharides found on the AG. The acyl transfer reaction between acyl donor 1 and acceptors 2, 3, and 9 in the presence of ag85C from Mycobacterium tuberculosis (M. tuberculosis) resulted in the formation of esters, methyl 2, 5-di-O-octanoyl-alpha-D-arabinofuranoside (10), methyl 5-O-octanoyl-beta-D-arabinofuranoside (11), and methyl 2-O-(5-O-octanoyl-beta-D-arabinofuranosyl)-5-O-octanoyl-alpha-D-arabinofuranoside (12) in 2 h, 2 h and 8 h, respectively. The initial velocities of the reactions were determined with a newly developed assay for acyltransferases. As expected, the regioselectivity corresponds to mycolylation patterns found at the terminus of the AG in M. tuberculosis. The study shows that D-arabinose-based derivatives are capable of acting as substrates for ag85C-mediated acyl-transfer and the acyl glycoside 1 can be used in lieu of TMM extracted from bacteria to study ag85-mediated acyl-transfer and inhibition leading to the better understanding of the ag85 protein class.

The identification and location of succinyl residues and the characterization of the interior arabinan region allow for a model of the complete primary structure of Mycobacterium tuberculosis mycolyl arabinogalactan

The complex cell wall of Mycobacterium tuberculosis is the hallmark of acid fast bacteria and is responsible for much of its physiological characteristics. Hence, much effort has been made to determine its primary structure. Such studies have been hampered by its extreme complexity. Also, its insolubility leads to difficulties determining the presence or absence of base labile groups. We have used an endogenous arabinase to solubilize the arabinan region of the cell wall and have shown using mass spectrometry and NMR that succinyl esters are present on O2 of the inner-branched 1,3,5-alpha-d-arabinofuranosyl residues. In addition, an inner arabinan region of 14 linear alpha-1,5 arabinofuranosyl residues has been identified. These and earlier results now allow the presentation of a model of the entire primary structure of the mycobacterial mycolyl arabinogalactan highlighted by three arabinan chains of 31 residues each.

The envelope layers of mycobacteria with reference to their pathogenicity

The review discusses current knowledge of the biosynthesis, composition and arrangement of the mycobacterial envelope, describes the biological activities of the constituents and considers how these activities may be relevant to the pathology of mycobacterial disease. The envelope possesses three structural components: plasma membrane, wall and capsule. Although the major biomolecules occurring in each of these parts are known, the distribution of numerous minor substances is poorly understood; an attempt has been made to assign them to particular positions on rational grounds. The plasma membrane appears to be a typical bacterial membrane but, though vital to the mycobacterium, probably plays little part in pathological processes. The wall partly resembles a Gram-positive wall, but is unusual in having a layer of lipid (mycolate esters) which is probably arranged to form a permeability barrier to polar molecules. The capsule, whose chemical composition has only recently been recognized, consists of polysaccharide and protein with traces of lipid; the arrangement of these components is imperfectly understood. Constituents of all parts of the envelope have biological activities which may be relevant. The likely importance of these activities in the overall effect of the envelope is considered.

Mechanisms of pathogenicity in mycobacteria

The purpose of this article is to review current knowledge about the mechanisms of pathogenicity of mycobacteria. The following aspects of the problem are discussed: chemically-defined compounds implicated in the mechanisms of pathogenicity; location in the cell wall of these compounds and their biological activities; mechanisms of intracellular survival of pathogenic mycobacteria as compared to intracellular killing of non-pathogenic mycobacteria; and pathogenesis of mycobacterial infection. The future prospects in the elucidation of the mechanisms of pathogenicity and their possible application for a better control of mycobacterial diseases are briefly discussed.

Leprosy

Leprosy affects over 10 million people in the world. The disease is a model of graded cell-mediated immunity, in this case to the causative organism, Mycobacterium leprae. The clinical manifestations are due to (i) bacterial progression, (ii) immunologic responses of the host, (iii) peripheral nerve damage due to either or both bacterial progression and immunologic responses of the host, and (iv) preventable secondary deformities following nerve damage, which account for most of the stigma of the disease. Treatment modalities are now available to control or minimize the effects of bacterial progression, harmful immunologic responses of the host, peripheral nerve damage, and secondary deformities. Unique biochemical characteristics of M. leprae reside in the cell wall and associated macromolecules. Some of these molecules are potent immunogens in humans, while others constitute the structural integrity of the bacillus. Proteins of M. leprae are currently under intensive investigation as a result of deoxyribonucleic acid cloning of M. leprae genes. Structure-function and antigenic relationships of M. leprae proteins should become available by using recombinant deoxyribonucleic acid procedures coupled with T- and B-cell cloning to advance our understanding of the immunologic reactions encountered in Hansen's disease. Until recently, the study of the immunology of leprosy has been stymied by the lack of immunologically specific M. leprae antigens. The definition of specific antigens and production of recombinant and synthetic immunologic reagents have fostered state-of-the-art research efforts into new immunodiagnostic procedures and development of a leprosy vaccine. Also discussed is progress in understanding of the mechanism(s) underlying the M. leprae-specific immunodeficiency associated with lepromatous leprosy, including the role of suppressor T cells and defective macrophage function. Metabolic studies of M. leprae suggest intact catabolic pathways and energy generation with purine bases and catalase as possible growth factors. Special attention may also need to be given to biophysical parameters for eventual in vitro cultivation. Rapid in vitro systems, using quantitation of bacillary metabolic activity, may soon replace the lengthy mouse footpad test for determining the viability and drug susceptibility of the leprosy bacillus.

Characterization of distinct layers of the Mycobacterium avium envelope in respect of their composition by fatty acids, proteins, oligosaccharides and antigens

The distribution of fatty acids, proteins, polysaccharides and antigens in subcellular fractions of Mycobacterium avium is described. Significant qualitative differences in the chemical composition of the various fractions have been used to further characterize the tripartite structure of the cell wall. In the outer dense layer (POL), in addition to previously described complex amphiphatic lipids, new oligosaccharides (lipooligosaccharides?) and a major glycoprotein were located; and it was found that tuberculostearic acid (TSA) esterified the phospholipids of this outerlayer. Judging from the data, it was proposed that the phospholipids formed a basic matrix monolayer in which other compounds of the POL intercalated. It was suggested that in an aqueous environment the hydrophobic ends of the phospholipids oriented to face the mycolic acid residues of the cell wall skeletons (or CWS) to form the 12 nm thick electron transparent layer. The purified CWS contained alpha-, keto-, and dicarboxylic mycolic acids; alanine, glutamic acid and diaminopimelic acid; and arabinose and galactose. Two additional nonidentified amino acids and an unidentified sugar were found in the CWS. Also, in the CWS the fatty acids: palmitic acid (21.8%), oleic acid (4.3%), stearic acid (9.2%) and TSA (4.3%), were detected. The main fatty acids detected in the cytoplasmic membrane (CM) were palmitic (20%), oleic (14.5%) and stearic (8.6%) acids. Mycolic acids and TSA were absent in the CM phospholipids. The major proteins of the CM (86, 40, and 26 Kd proteins) were distinct from the major proteins detected in the cytosol (CYT) fraction (43, 36, and 19 Kd proteins). A 58 Kd protein was present in both the CM and the CYT. The CYT and CM antigens were found absent in surface antigens extracted using sodium dodecyl sulphate (SDS).

Biological, chemical, immunological and staining properties of bacteria isolated from tissues of leprosy patients

Two kinds of microorganisms are found in tissue of leprosy patients: Mycobacterium leprae (ML) and leprosy derived corynebacteria (LDC). ML from untreated patients has an alcohol-acid-fastness, which is lost upon treatment with antibiotics and immune response (tuberculoid leprosy). Vulnerable ML thus produced can be reversibly de-stained by organic solvent: in tissue sections from tuberculoid and treated patients, more bacteria are, thus, revealed by the Wade-Fite than by the Ziehl-Neelsen procedure. Organisms of genera Corynebacterium, Mycobacterium and Nocardia (CMN group), have DNA with %GC contents of 50-70, 69-72, and 68-70 respectively. GC values of DNA from ML and LDC are close to 56%. DNA from different LDC strains display high homology among them and low homology with reference corynebacteria. CMN cell wall consists of interconnected peptidoglycan and polysaccharide-mycolate complex. Peptidoglycan of LDC (and known CMN) has the polysaccharide backbone linked to a tetrapeptide of L-Ala, D-Glu, m-DAP (meso-diaminopimelate), D-Ala. In ML, L-Ala is replaced by glycine. Mycobacterial wall polysaccharides (that of ML is unknown) are branched arabinogalactans with end arabinoses linked to C70 to C90 mycolates. LDC peripheral polysaccharides are arabinogalactomannans with arabinose and mannose lateral strands. Mycolic acids of LDC are of corynomycolic type (C32, C34 and C36 with 1-4 double bonds) and those of ML are of mycobacterial type. Components of CMN wall and cytoplasm are immunologically active as antigens (polysaccharides, proteins), haptens (lipids) and adjuvants (peptidoglycans). Strong intrageneric and weak intergenera crossreactions are observed among CMN bacteria: LDC preparations, however, crossreact strongly with ML and mycobacteria, and weakly with reference corynebacteria. LDC in leprosy tissues can, thus, be revealed as well by fluorescent anti-LDC antisera as by anti-ML antisera. The main crossreacting component is antigen M1 of LDC, which corresponds to antigens Ag 7 of ML and Ag60 of BCG, the active components of lepromin and tuberculin (known reagents for cutaneous tests). Antigen M1 has a polysaccharide moiety crossreacting with the wall polysaccharide of LDC.(ABSTRACT TRUNCATED AT 400 WORDS)

Adhesion of a Mycobacterium sp. to cellulose diacetate membranes used in reverse osmosis

The kinetics of adhesion of a Mycobacterium sp. to cellulose diacetate reverse-osmosis membranes is described. This Mycobacterium sp. (strain BT2-4) was previously implicated in the initial stages of reverse-osmosis membrane biofouling at a wastewater reclamation facility. Adhesion of BT2-4 cells to the cellulose diacetate membrane surfaces occurred within 1 to 2 h at 30 degrees C and exhibited saturation-type kinetics which conformed closely to the Langmuir adsorption isotherm (Pearson r correlation coefficient = 0.977), a mathematical expression describing the partitioning of substances between a solution and solid-liquid interface. This suggests that the cellulose diacetate membrane surfaces may possess a finite number of available binding sites to which the mycobacteria can adhere. Treatment of the attached mycobacteria with different enzymes suggested that cell surface polypeptides, alpha-1, 4- or alpha-1,6-linked glucan polymers, and carboxyl ester bond-containing substances (possibly peptidoglycolipids) may be involved in mycobacterial adhesion. The possible implication of these findings for reverse-osmosis membrane biofouling are discussed.

Mycobacterium

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Corynebacterium diphtheriae and its relatives

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