Monocyte adhesion to xenogeneic endothelium during laminar flow is dependent on alpha-Gal-mediated monocyte activation

Monocytes are the predominant inflammatory cell recruited to xenografts and participate in delayed xenograft rejection. In contrast to allogeneic leukocytes that require up-regulation of endothelial adhesion molecules to adhere and emigrate into effector tissues, we demonstrate that human monocytes adhere rapidly to unstimulated xenogeneic endothelial cells. The major xenoantigen galactosealpha(1,3)galactosebeta(1,4)GlcNAc-R (alpha-gal) is abundantly expressed on xenogeneic endothelium. We have identified a putative receptor for alpha-gal on human monocytes that is a member of the C-type family of lectin receptors. Monocyte arrest under physiological flow conditions is regulated by alpha-gal, because cleavage or blockade results in a dramatic reduction in monocyte adhesion. Recruitment of human monocytes to unactivated xenogeneic endothelial cells requires both alpha(4) and beta(2) integrins on the monocyte; binding of alpha-gal to monocytes results in rapid activation of beta(2), but not alpha(4), integrins. Thus, activation of monocyte beta(2) integrins by alpha-gal expressed on xenogeneic endothelium provides a mechanism that may explain the dramatic accumulation of monocytes in vivo.

Characterization of the highly efficient sucrose isomerase from Pantoea dispersa UQ68J and cloning of the sucrose isomerase gene

Sucrose isomerase (SI) genes from Pantoea dispersa UQ68J, Klebsiella planticola UQ14S, and Erwinia rhapontici WAC2928 were cloned and expressed in Escherichia coli. The predicted products of the UQ14S and WAC2928 genes were similar to known SIs. The UQ68J SI differed substantially, and it showed the highest isomaltulose-producing efficiency in E. coli cells. The purified recombinant WAC2928 SI was unstable, whereas purified UQ68J and UQ14S SIs were very stable. UQ68J SI activity was optimal at pH 5 and 30 to 35 degrees C, and it produced a high ratio of isomaltulose to trehalulose (>22:1) across its pH and temperature ranges for activity (pH 4 to 7 and 20 to 50 degrees C). In contrast, UQ14S SI showed optimal activity at pH 6 and 35 degrees C and produced a lower ratio of isomaltulose to trehalulose (<8:1) across its pH and temperature ranges for activity. UQ68J SI had much higher catalytic efficiency; the Km was 39.9 mM, the Vmax was 638 U mg(-1), and the Kcat/Km was 1.79 x 10(4) M(-1) s(-1), compared to a Km of 76.0 mM, a Vmax of 423 U mg(-1), and a Kcat/Km of 0.62 x 10(4) M(-1) s(-1) for UQ14S SI. UQ68J SI also showed no apparent reverse reaction producing glucose, fructose, or trehalulose from isomaltulose. These properties of the P. dispersa UQ68J enzyme are exceptional among purified SIs, and they indicate likely differences in the mechanism at the enzyme active site. They may favor the production of isomaltulose as an inhibitor of competing microbes in high-sucrose environments, and they are likely to be highly beneficial for industrial production of isomaltulose.

Generation of Novel Landomycins M and O through Targeted Gene Disruption

Two genes from Streptomyces cyanogenous S136 that encode the reductase LanZ4 and the hydroxylase LanZ5, which are involved in landomycin A biosynthesis, were characterized by targeted gene inactivation. Analyses of the corresponding mutants as well as complementation experiments have allowed us to show that LanZ4 and LanZ5 are responsible for the unique C-11-hydroxylation that occurs during landomycin biosynthesis. Compounds accumulated by the lanZ4/Z5 mutants are the previously described landomycin F and the new landomycins M and O.

Lactosucrose production by various microorganisms harboring levansucrase activity

Production of the artificial sweetener, lactosucrose, by various microorganisms containing levansucrase activity was investigated. Of the tested bacteria, Bacillus subtilis was the most effective producer using lactose as an acceptor and sucrose as a fructosyl donor. Lactosucrose production by this strain was optimal at pH 6.0 and 55 degrees C whereupon 181 g lactosucrose l(-1) was produced from 225 g lactose l(-1) and 225 g sucrose l(-1) in 10 h.

Molecular cloning of levan fructotransferase gene from Arthrobacter ureafaciens K2032 and its expression in Escherichia coli for the production of difructose dianhydride IV

AIMS

To clone and overexpress a novel levan fructotransferase gene lftA from Arthrobacter ureafaciens K2032.

METHODS AND RESULTS

The lftA gene, encoding a levan fructotransferase (LFTase) of 521 amino acids (aa) residues, was cloned from the genomic DNA of A. ureafaciens K2032, and overexpressed in Escherichia coli. The recombinant LFTase overexpressed in E. coli was then used to produce a difructose dianhydride (DFA IV) from levan. DFA IV crystals with 97% purity could be obtained from the reaction mixture in 83.7% yield by using a natural crystallization method.

CONCLUSIONS

The lftA gene cloned from A. ureafaciens K2032 encode a novel levan fructotransferase which produces difructose dianhydride (DFA IV) from levan.

SIGNIFICANCE AND IMPACT OF THE STUDY

Levan fructotransferase is a useful enzyme with great promise in the production of DFA IV and various fructosides.

Heparin-binding growth factor, pleiotrophin, mediates neuritogenic activity of embryonic pig brain-derived chondroitin sulfate/dermatan sulfate hybrid chains

Chondroitin sulfate (CS) and dermatan sulfate (DS) chains play roles in the central nervous system. Most notably, CS/DS hybrid chains (E-CS/DS) purified from embryonic pig brains bind growth factors and promote neurite outgrowth toward embryonic mouse hippocampal neurons in culture. However, the neuritogenic mechanism is not well understood. Here we showed that pleiotrophin (PTN), a heparin-binding growth factor, produced mainly by glia cells, was the predominant binding partner for E-CS/DS in the membrane-associated protein fraction of neonatal rat brain. The CS/DS chains were separated on a PTN column into unbound, low affinity, and high affinity fractions. The latter two fractions promoted outgrowth of dendrite- and axon-like neurites, respectively, whereas the unbound fraction showed no such activity. The activity of the low affinity fraction was abolished by an anti-PTN antibody or when glia cells were removed from the culture. In contrast, the high affinity fraction displayed activity under both these conditions. Hence, PTN mainly from glia cells mediated the activity of the low affinity but not the high affinity fraction. The anti-CS antibody 473HD neutralized the neuritogenic activities of both fractions. Interaction analysis indicated that the 473HD epitope and PTN-binding domains in the E-CS/DS chains largely overlap. The three affinity subfractions differed in disaccharide composition and the distribution of l-iduronic acid-containing disaccharides along the chains. Oversulfated disaccharides and nonconsecutive iduronic acid-containing units were the requirements for the E-CS/DS chains to bind PTN and to exhibit the neuritogenic activities. Thus, CS subpopulations with distinct structures in the mammalian brain play different roles in neuritogenesis through distinct molecular mechanisms, at least in part by regulating the functions of growth factors.

Tailoring modification of deoxysugars during biosynthesis of the antitumour drug chromomycin A by Streptomyces griseus ssp. griseus

Chromomycin A3 is a member of the aureolic acid group family of antitumour drugs. Three tailoring modification steps occur during its biosynthesis affecting the sugar moieties: two O-acetylations and one O-methylation. The 4-O-methylation in the 4-O-methyl-D-oliose moiety of the disaccharide chain is catalysed by the cmmMIII gene product. Inactivation of this gene generated a chromomycin-non-producing mutant that accumulated three unmethylated derivatives containing all sugars but differing in the acylation pattern. Two of these compounds were shown to be substrates of the methyltransferase as determined by their bioconversion into chromomycin A2 and A3 after feeding these compounds to a Streptomyces albus strain expressing the cmmMIII gene. The same single membrane-bound enzyme, encoded by the cmmA gene, is responsible for both acetyl transfer reactions, which convert a relatively inactive compound into the bioactive chromomycin A3. Insertional inactivation of this gene resulted in a mutant accumulating a dideacetylated chromomycin A3 derivative. This compound, lacking both acetyl groups, was converted in a two-step reaction via the 4E-monoacetylated intermediate into chromomycin A3 when fed to cultures of S. albus expressing the cmmA gene. This acetylation step would occur as the last step in chromomycin biosynthesis, being a very important event for self-protection of the producing organism. It would convert a molecule with low biological activity into an active one, in a reaction catalysed by an enzyme that is predicted to be located in the cell membrane.

Targeted mutagenesis of the Mycobacterium smegmatis mca gene, encoding a mycothiol-dependent detoxification protein

Mycothiol (MSH), a functional analogue of glutathione (GSH) that is found exclusively in actinomycetes, reacts with electrophiles and toxins to form MSH-toxin conjugates. Mycothiol S-conjugate amidase (Mca) then catalyzes the hydrolysis of an amide bond in the S conjugates, producing a mercapturic acid of the toxin, which is excreted from the bacterium, and glucosaminyl inositol, which is recycled back to MSH. In this study, we have generated and characterized an allelic exchange mutant of the mca gene of Mycobacterium smegmatis. The mca mutant accumulates the S conjugates of the thiol-specific alkylating agent monobromobimane and the antibiotic rifamycin S. Introduction of M. tuberculosis mca epichromosomally or introduction of M. smegmatis mca integratively resulted in complementation of Mca activity and reduced levels of S conjugates. The mutation in mca renders the mutant strain more susceptible to electrophilic toxins, such as N-ethylmalemide, iodoacetamide, and chlorodinitrobenzene, and to several oxidants, such as menadione and plumbagin. Additionally we have shown that the mca mutant is also more susceptible to the antituberculous antibiotic streptomycin. Mutants disrupted in genes belonging to MSH biosynthesis are also more susceptible to streptomycin, providing further evidence that Mca detoxifies streptomycin in the mycobacterial cell in an MSH-dependent manner.

Phylogenetic expression of Galalpha1-4Gal on avian glycoproteins: glycan differentiation inscribed in the early history of modern birds

Glycoproteins containing Galalpha1-4Gal (galabiose) had been rarely found in vertebrates, except in a few species of birds and amphibians. We had previously reported that pigeon (Columba livia) egg white and serum glycoproteins are rich in N-glycans with Galalpha1-4Gal at nonreducing termini. To investigate the origin of Galalpha1-4Gal expression in avian evolution, we examined the presence of Galalpha1-4Gal glycoproteins in egg whites from 20 orders, 88 families, 163 genera, and 181 species of birds, as probed by Western blot with Griffonia simplicifolia-I lectin (terminal alpha-Gal/GalNAc-specific) and anti-P(1) mAb (Galalpha1-4Galbeta1-4GlcNAcbeta1-specific). One of the significant observations is the total absence of Galalpha1-4Gal glycoproteins in Struthioniformes (four species), Tinamiformes (three species), Craciformes (two species), Galliformes (14 species), and Anseriformes (10 species), which are phylogenetically separated from other orders at earlier stage of modern bird diversification (100-65 million years ago). The presence or absence of Galalpha1-4Gal glycoproteins in other avian orders varied by the species (104 species positive, and 44 species negative), even though some of them belong to the same order or family. Our results revealed that the expression of Galalpha1-4Gal glycoproteins is not rare among avians, and is correlated with the phylogeny. The expression was most likely differentiated at earlier stage of diversification in modern birds, but some birds might have lost the facility for the expression relatively recently.

α-Mannosidase-catalyzed synthesis of a (1→2)-α-d-rhamnodisaccharide derivative

Enzymatic transglycosylation using p-nitrophenyl alpha-D-rhamnopyranoside as the glycosyl donor and 6equiv of ethyl 1-thio-alpha-D-rhamnopyranoside as the glycosyl acceptor yielded a D-rhamnooligosaccharide derivative. The reaction was catalyzed by jack bean alpha-mannosidase in a 1:1 (v/v) mixture of 0.1 M sodium citrate buffer (pH4.5)-MeCN at 25 degrees C. The enzyme exhibited high catalytic activity for the reaction, to afford in 32.1% isolated yield (based on donor substrate) ethyl alpha-D-rhamnopyranosyl-(1-->2)-1-thio-alpha-D-rhamnopyranoside, which is a derivative of the common oligosaccharide unit of the antigenic lipopolysaccharides from Pseudomonas.

Metabolic fate of jasmonates in tobacco bright yellow-2 cells

Jasmonic acid and methyl jasmonate play an essential role in plant defense responses and pollen development. Their levels are temporarily and spatially controlled in plant tissue. However, whereas jasmonate biosynthesis is well studied, metabolic pathways downstream of jasmonic acid are less understood. We studied the uptake and metabolism of jasmonic acid and methyl jasmonate in tobacco (Nicotiana tabacum) Bright Yellow-2 suspension culture. We found that upon uptake, jasmonic acid was metabolized to its Glc and gentiobiose esters, and hydroxylation at C-11 or C-12 occurred. Free hydroxylated jasmonates were the preferential fraction of the culture medium. Upon hydrolysis of methyl jasmonate to jasmonic acid, a similar set of conversions occurs. In contrast to jasmonic acid, none of its derivatives interfere with the G2/M transition in synchronized tobacco Bright Yellow-2 cells.

Aberrant expression ofα-Gal on primary human endothelium does not confer susceptibility to NK cell cytotoxicity or increased NK cell adhesion

The contribution of Gal alpha 1,3Gal (alpha-Gal) to cell-mediated organ xenograft rejection is controversial. We have used recombinant lentiviruses encoding a porcine alpha 1,3 galactosyltransferase (alpha 1,3GalT) to obtain alpha-Gal-expressing primary human aortic endothelial cells (HAEC) at a frequency of 70-90%. These cells were compared to non-transduced and mock-transduced HAEC with regard to their susceptibility to human NK cell-mediated lysis, ability to stimulate IFN-gamma production by NK cells, and support of NK cell adhesion under static and dynamic conditions. Using green fluorescent protein (GFP) as a reporter gene, it was shown that the frequency of green fluorescent HAEC increased until day 5 post-transduction, and at a multiplicity of infection of 2.5, it reached 98%. Lentiviral transduction did not result in activation of HAEC, and transduced HAEC responded as expected to TNF-alpha and IFN-gamma stimulation. No differences were detected between non-alpha-Gal- and alpha-Gal-expressing HAEC in terms of their susceptibility to NK cell-mediated lysis, ability to stimulate IFN-gamma production by NK cells, or ability to support NK cell adhesion under static and dynamic conditions. In conclusion, these data argue against an important role for the alpha-Gal epitope in the direct interaction between endothelium and NK cells and prove that recombinant lentiviruses are efficient gene carriers for primary human endothelial cells.

Molecular cloning and characterization of β1,4-N-acetylgalactosaminyltransferases IV synthesizingN,N′-diacetyllactosediamine1

A sequence highly homologous to beta1,4-N-acetylgalactosaminyltransferase III (beta4GalNAc-T3) was found in a database of human expressed sequence tags. The full-length open reading frame of the gene, beta4GalNAc-T4 (GenBank accession number AB089939), was cloned using the 5' rapid amplification of cDNA ends method. It encodes a typical type II transmembrane protein of 1039 amino acids having 42.6% identity with beta4GalNAc-T3. The recombinant enzyme transferred N-acetylgalactosamine to N-acetylglucosamine-beta-benzyl with a beta1,4-linkage to form N,N'-diacetyllactosediamine as did beta4GalNAc-T3. In specificity toward oligosaccharide acceptor substrates, it was quite similar to beta4GalNAc-T3 in vitro, however, the tissue distributions of the two enzymes were quite different. These results indicated that the two enzymes have similar roles in different tissues.

Enzymatic synthesis of chondroitin and its derivatives catalyzed by hyaluronidase

The enzymatic polymerization to provide synthetic chondroitin and its derivatives is reported here, the first example of such in vitro synthesis to date. N-Acetylchondrosine (GlcAbeta(1-->3)GalNAc) oxazoline (1a) and its derivatives (1b-1f) were designed and synthesized as novel transition state analogue substrate monomers for catalysis by hyaluronidase. Hyaluronidase is a hydrolysis enzyme of chondroitin that also catalyzes the formation of repeated glycosidic bonds in in vitro synthesis, rather than in the catabolic direction. Monomers of 2-methyl (1a), 2-ethyl (1b), and 2-vinyl (1f) oxazoline derivatives were polymerized using this enzyme, via ring-opening polyaddition with total control of regioselectivity and stereochemistry. These reactions provided the corresponding synthetic chondroitin (natural type; N-acetyl, 2a) and the derivatives (unnatural type) with N-propionyl (2b) and N-acryloyl (2f) functional groups at the C2 position of all the galactosamine units, in good yields. Monomers of 2-n-propyl (1c) and 2-isopropyl (1d) oxazoline derivatives were polymerized to produce 2c and 2d in low yield. The 2-phenyl oxazoline derivative (1e) did not afford any enzyme-catalyzed products. M(n) values of 2a and 2b reached 4800 and 4000, respectively. The M(n) value of 2a corresponds to that of the naturally occurring chondroitin. Thus, hyaluronidase catalysis allows the in vitro production of not only natural type but also the formation of unnatural type chondroitins.

Induction of 3'-O-beta-D-ribofuranosyl adenosine during compatible, but not during incompatible, interactions of Arabidopsis thaliana or Lycopersicon esculentum with Pseudomonas syringae pathovar tomato

All hitherto identified aromatic compounds accumulating in leaves of Arabidopsis thaliana (L.) Heynh. upon infection with virulent or avirulent strains of Pseudomonas syringae pathovar tomato ( Pst) were indolic metabolites. We now report the strong accumulation of a novel type of natural product, 3'-O-beta-D-ribofuranosyl adenosine (3'RA), exclusively during compatible interactions. In contrast to the various indolic metabolites, 3'RA was undetectable in incompatible interactions of A. thaliana leaves with an avirulent Pst strain, as well as in uninfected control leaves. A similar, strong induction of 3'RA was observed in compatible but, again, not in incompatible interactions of Pst with its natural host, Lycopersicon esculentum. The strength of the effect and its confinement to compatible interactions suggests that it may be applicable as a diagnostic tool.

Crystal Structure of MshB from Mycobacterium tuberculosis , a Deacetylase Involved in Mycothiol Biosynthesis

All living species require protection against the damaging effects of the reactive oxygen species that are a natural by-product of aerobic life. In most organisms, glutathione is a critical component of these defences, maintaining a reducing environment inside cells. Some bacteria, however, including pathogenic mycobacteria, use an alternative low molecular mass thiol compound called mycothiol (MSH) for this purpose. Enzymes that synthesize MSH are attractive candidates for the design of novel anti-TB drugs because of the importance of MSH for mycobacterial life and the absence of such enzymes in humans. We have determined the three-dimensional structure of MshB (Rv1170), a metal-dependent deacetylase from Mycobacterium tuberculosis that catalyses the second step in MSH biosynthesis. The structure, determined at 1.9A resolution by X-ray crystallography (R=19.0%, R(free)=21.4%), reveals an alpha/beta fold in which helices pack against a seven-stranded mostly parallel beta-sheet. Large loops emanating from the C termini of the beta-strands enclose a deep cavity, which is the location of the putative active site. At the bottom of this cavity is a metal-binding site associated with a sequence motif AHPDDE that is invariant in all homologues. An adventitiously bound beta-octylglucoside molecule, used in crystallization, enables us to model the binding of the true substrate and propose a metal-dependent mechanistic model for deacetylation. Sequence comparisons indicate that MshB is representative of a wider family of enzymes that act on substituted N-acetylglucosamine residues, including a deacetylase involved in the biosynthesis of glycosylphosphatidylinositol (GPI) anchors in eukaryotes.

Mycothiol is essential for growth of Mycobacterium tuberculosis Erdman

Mycothiol (MSH) is the major low-molecular-mass thiol in mycobacteria and is associated with the protection of Mycobacterium tuberculosis from toxic oxidants and antibiotics. The biosynthesis of MSH is a multistep process, with the enzymatic reaction designated MshC being the ligase step in MSH production. A targeted disruption of the native mshC gene in M. tuberculosis Erdman produced no viable clones possessing either a disrupted mshC gene or reduced levels of MSH. However, when a second copy of the mshC gene was incorporated into the chromosome prior to the targeted disruption, multiple clones having the native gene disrupted and the second copy of mshC intact were obtained. These clones produced normal levels of MSH. These results demonstrate that the mshC gene and, more generally, the production of MSH are essential for the growth of M. tuberculosis Erdman under laboratory conditions.

Application of selectively acylated glycosides for the alpha-galactosidase-catalyzed synthesis of disaccharides

4-Nitrophenyl alpha-D-galactopyranosyl-(1-->3)-6-O-acetyl-alpha-D-galactopyranoside was prepared in a transglycosylation reaction catalyzed by alpha-D-galactosidase from Talaromyces flavus using 4-nitrophenyl alpha-D-galactopyranoside as a glycosyl donor and 4-nitrophenyl 6-O-acetyl-alpha-D-galactopyranoside as an acceptor. 4-Nitrophenyl 6-O-acetyl-alpha-D-galactopyranoside and 4-nitrophenyl 6-O-acetyl-beta-D-galactopyranoside were prepared in a regioselective enzymic transesterification in pyridine-acetone catalyzed by the lipase PS from Burkholderia cepacia. A series of water-miscible organic solvents (acetone, acetonitrile, dimethylformamide, dimethyl sulfoxide, 1,4-dioxane, 2-methoxyethanol, pyridine, 2-methylpropan-2-ol, tetrahydrofuran, propargyl alcohol) were used as co-solvents in this enzymic reaction. Their influence on the activity and stability of the alpha-galactosidase from T. flavus was established. 2-Methylpropan-2-ol and acetone (increasing the solubility of the modified substrate acceptors and displaying the minimum impairment of the activity and stability of the enzyme) were used as co-solvents in transglycosylation reactions.

Expression of human alpha-galactosidase leads to reduction of major xenoepitope Galalpha(1,3) Gal in NIH 3T3 cell

AIM

To examine the effects of the expression of alpha-galactosidase on the expression of the major xenoepitope Galalpha(1,3) Gal (G antigen) in NIH 3T3 cell.

METHODS

The expression levels of G antigen and H antigen and binding of human natural antibodies (IgG and IgM) and complement (C3c) to NIH 3T3 cells were analyzed by flow cytometry. Western blot was employed to further determine the expression of glycoproteins of G antigen. Cytolysis assay with normal human serum was performed by MTT assay.

RESULTS

In transfectants, Western blot showed that the binding of human IgG to glycosylated proteins located on the cell membrane was decreased, even abrogated totally. Together with the reduced binding of Gs-IB4 (Griffonia simplicifolia) to transfectants, the stable expression of human alpha-galactosidase effectively inhibited Galalpha(1,3) Gal, Gal epitope synthesis in NIH 3T3 cell. As a result, the xenoreactivities of human IgG, IgM, and C3c were reduced by 73.4 %, 22.3 % and 47.9 %, respectively, while the cell lysis mediated by human XNA and complements was decreased by 42.4 %.

CONCLUSION

The stable expression of human alpha-galactosidase in NIH 3T3 cell strongly inhibits the expression of Gal epitopes, resulting in abrupt reduction in xenorejection induced by human serum.

Characterization of a heparan sulfate 3-O-sulfotransferase-5, an enzyme synthesizing a tetrasulfated disaccharide

Heparan sulfate d-glucosaminyl 3-O-sulfotransferases (3-OSTs) catalyze the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to position 3 of the glucosamine residue of heparan sulfate and heparin. A sixth member of the human 3-OST family, named 3-OST-5, was recently reported (Xia, G., Chen, J., Tiwari, V., Ju, W., Li, J.-P., Malmstrom, A., Shukla, D., and Liu, J. (2002) J. Biol. Chem. 277, 37912-37919). In the present study, we cloned putative catalytic domain of the human 3-OST-5 and expressed it in insect cells as a soluble enzyme. Recombinant 3-OST-5 only exhibited sulfotransferase activity toward heparan sulfate and heparin. When incubated heparan sulfate with [35S]PAPS, the highest incorporation of35S was observed, and digestion of the product with a mixture of heparin lyases yielded two major35S-labeled disaccharides, which were determined as DeltaHexA-GlcN(NS,3S,6S) and DeltaHexA(2S)-GlcN(NS,3S) by further digestion with 2-sulfatase and degradation with mercuric acetate. However, when used heparin as acceptor, we identified a highly sulfated disaccharide unit as a major product. This had a structure of DeltaHexA(2S)-GlcN(NS,3S,6S). Quantitative real-time PCR analysis revealed that 3-OST-5 was highly expressed in fetal brain, followed by adult brain and spinal cord, and at very low or undetectable levels in the other tissues. Finally, we detected a tetrasulfated disaccharide unit in bovine intestinal heparan sulfate. To our knowledge, this is the first report to describe not only the natural occurrence of tetrasulfated disaccharide unit but also the enzymatic formation of this novel structure.

Production of galactinol from sucrose by plant enzymes

Galactinol, 1-O-(alpha-D-galactopyranosyl)-myo-inositol, was produced from sucrose as a starting material. UDP-Glc was prepared with sucrose and UDP using sucrose synthase partially purified from sweet potato roots. Then, the UDP-Glc was converted to UDP-Gal using yeast UDP-Gal 4-epimerase from a commercial source. Finally, galactinol was produced from the UDP-Gal and myo-inositol using galactinol synthase partially purified from cucumber leaves. The product was identified as galactinol by the retention times of HPLC, alpha-galactosidase digestion, and NMR spectrometry.

Synthesis of 2-deoxy-2-C-alkylglucosides of myo-inositol as possible inhibitors of a N-deacetylase enzyme in the biosynthesis of mycothiol

Two new analogues of 1-D-1-O-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-myo-inositol, a biosynthetic intermediate in the production of mycothiol in the Mycobacteria have been synthesized. Both the 2-deoxy-2-C-(2'-hydroxypropyl)-D-glucoside 5, and the 2-deoxy-2-C-(2'-oxopropyl)-D-glucoside 6, are derived from fully benzylated 1-D-1-O-(2-C-allyl-2-deoxy)-D-glucopyranosyl)-myo-inositol 20, readily assembled via a protected 2-C-allyl-2-deoxyglucosyl fluoride. Both 5 and 6 inhibit the incorporation of [3H]inositol by whole cells of Mycobacterium smegmatis into a number of metabolites which contain inositol.

Distinct sucrose isomerases catalyze trehalulose synthesis in whiteflies, Bemisia argentifolii, and Erwinia rhapontici

Isomaltulose [alpha-D-glucopyranosyl-(1,6)-D-fructofuranose] and trehalulose [alpha-D-glucopyranosyl-(1,1)-D-fructofuranose] are commercially valuable sucrose-substitutes that are produced in several microorganisms by the palI gene product, a sucrose isomerase. Trehalulose also occurs in the silverleaf whitefly, Bemisia argentifoli, as the major carbohydrate in the insect's honeydew. To determine if the enzyme that synthesizes trehalulose in whiteflies was similar to the well-characterized sucrose isomerase from microbial sources, the properties of the enzymes from whiteflies and the bacterium, Erwinia rhapontici, were compared. Partial purification of both enzymes showed that the enzyme from whiteflies was a 116 kD membrane-associated polypeptide, in contrast to the enzyme from E. rhapontici, which was soluble and 66 kD. The enzyme from E. rhapontici converted sucrose to isomaltulose and trehalulose in a 5:1 ratio, whereas the enzyme from whiteflies produced only trehalulose. Unlike the E. rhapontici enzyme, the whitefly enzyme did not convert isomaltulose to trehalulose, but both enzymes catalyzed the transfer of fructose to trehalulose using sucrose as the glucosyl donor. The results indicate that trehalulose synthase from whiteflies is structurally and functionally distinct from the sucrose isomerases described in bacteria. The whitefly enzyme is the first reported case of an enzyme that converts sucrose to exclusively trehalulose.

The glycosyltransferase gene encoding the enzyme catalyzing the first step of mycothiol biosynthesis (mshA)

Mycothiol is the major thiol present in most actinomycetes and is produced from the pseudodisaccharide 1D-myo-inosityl 2-acetamido-2-deoxy-alpha-D-glucopyranoside (GlcNAc-Ins). A transposon mutant of Mycobacterium smegmatis shown to be GlcNAc-Ins and mycothiol deficient was sequenced to identify a putative glycosyltransferase gene designated mshA. The ortholog in Mycobacterium tuberculosis, Rv0486, was used to complement the mutant phenotype.

MmpL8 is required for sulfolipid-1 biosynthesis and Mycobacterium tuberculosis virulence

Mycobacterium tuberculosis, the causative agent of human tuberculosis, is unique among bacterial pathogens in that it displays a wide array of complex lipids and lipoglycans on its cell surface. One of the more remarkable lipids is a sulfated glycolipid, termed sulfolipid-1 (SL-1), which is thought to mediate specific host-pathogen interactions during infection. However, a direct role for SL-1 in M. tuberculosis virulence has not been established. Here we show that MmpL8, a member of a large family of predicted lipid transporters in M. tuberculosis, is required for SL-1 production. The accumulation of an SL-1 precursor, termed SL(1278), in mmpL8 mutant cells indicates that MmpL8 is necessary for an intermediate step in the SL-1 biosynthesis pathway. We use a novel fractionation procedure to demonstrate that SL-1 is present on the cell surface, whereas SL(1278) is found exclusively in more internal layers. Importantly, we show that mmpL8 mutants are attenuated for growth in a mouse model of tuberculosis. However, SL-1 per se is not required for establishing infection as pks2 mutants, which are defective in an earlier step in SL-1 biosynthesis, have no obvious growth defect. Thus, we hypothesize that either MmpL8 transports molecules in addition to SL-1 that mediate host-pathogen interactions or the accumulation of SL(1278) in mmpL8 mutant cells interferes with other pathways required for growth during the early stages of infection.