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At least 19 recordsLinked to original sources
PubMed1983

Isomeric, anti-rhamnose antibodies having specificity for rhamnose-containing, streptococcal heteroglycans.

L-Rhamnose (6-deoxy-L-mannose) is a constituent carbohydrate unit of microbial, immunogenic heteroglycans and lipopolysaccharides, and often functions as the immunodeterminant group of such immunogens. Two types of anti-rhamnose antibody have now been isolated by affinity chromatography of immune sera obtained from rabbits immunized with vaccines of Streptococcus mutans, strain KI-R, and Streptococcus pneumoniae, type 32. The antibodies of one type were directed at a glycan of L-rhamnose, D-glucose, and D-galactose in the cell wall of S. mutans, and those of the other type, against a capsular glycan of L-rhamnose and D-glucose from S. pneumoniae. The two types of anti-rhamnose antibody were immunologically distinct, and showed no reciprocal cross-reactivity. Additional properties of the two types of antibody were determined; thus, both types of antibody were of the IgG class of immunoglobulins, both possessed molecular weights of 1.45 X 10(5), and both consisted of multiple or isomeric forms.

Antibody Specificity↗
PubMed2006

The structures of L-rhamnose isomerase from Pseudomonas stutzeri in complexes with L-rhamnose and D-allose provide insights into broad substrate specificity.

Pseudomonas stutzeri L-rhamnose isomerase (P. stutzeri L-RhI) can efficiently catalyze the isomerization between various aldoses and ketoses, showing a broad substrate specificity compared to L-RhI from Escherichia coli (E. coli L-RhI). To understand the relationship between structure and substrate specificity, the crystal structures of P. stutzeri L-RhI alone and in complexes with L-rhamnose and D-allose which has different configurations of C4 and C5 from L-rhamnose, were determined at a resolution of 2.0 A, 1.97 A, and 1.97 A, respectively. P. stutzeri L-RhI has a large domain with a (beta/alpha)(8) barrel fold and an additional small domain composed of seven alpha-helices, forming a homo tetramer, as found in E. coli L-RhI and D-xylose isomerases (D-XIs) from various microorganisms. The beta1-alpha1 loop (Gly60-Arg76) of P. stutzeri L-RhI is involved in the substrate binding of a neighbouring molecule, as found in D-XIs, while in E. coli L-RhI, the corresponding beta1-alpha1 loop is extended (Asp52-Arg78) and covers the substrate-binding site of the same molecule. The complex structures of P. stutzeri L-RhI with L-rhamnose and D-allose show that both substrates are nicely fitted to the substrate-binding site. The part of the substrate-binding site interacting with the substrate at the 1, 2, and 3 positions is equivalent to E. coli L-RhI, and the other part interacting with the 4, 5, and 6 positions is similar to D-XI. In E. coli L-RhI, the beta1-alpha1 loop creates an unique hydrophobic pocket at the the 4, 5, and 6 positions, leading to the strictly recognition of L-rhamnose as the most suitable substrate, while in P. stutzeri L-RhI, there is no corresponding hydrophobic pocket where Phe66 from a neighbouring molecule merely forms hydrophobic interactions with the substrate, leading to the loose substrate recognition at the 4, 5, and 6 positions.

Aldose-Ketose Isomerases↗
PubMed2001

Drug targeting Mycobacterium tuberculosis cell wall synthesis: genetics of dTDP-rhamnose synthetic enzymes and development of a microtiter plate-based screen for inhibitors of conversion of dTDP-glucose to dTDP-rhamnose.

An L-rhamnosyl residue plays an essential structural role in the cell wall of Mycobacterium tuberculosis. Therefore, the four enzymes (RmlA to RmlD) that form dTDP-rhamnose from dTTP and glucose-1-phosphate are important targets for the development of new tuberculosis therapeutics. M. tuberculosis genes encoding RmlA, RmlC, and RmlD have been identified and expressed in Escherichia coli. It is shown here that genes for only one isotype each of RmlA to RmlD are present in the M. tuberculosis genome. The gene for RmlB is Rv3464. Rv3264c was shown to encode ManB, not a second isotype of RmlA. Using recombinant RmlB, -C, and -D enzymes, a microtiter plate assay was developed to screen for inhibitors of the formation of dTDP-rhamnose. The three enzymes were incubated with dTDP-glucose and NADPH to form dTDP-rhamnose and NADP(+) with a concomitant decrease in optical density at 340 nm (OD(340)). Inhibitor candidates were monitored for their ability to lower the rate of OD(340) change. To test the robustness and practicality of the assay, a chemical library of 8,000 compounds was screened. Eleven inhibitors active at 10 microM were identified; four of these showed activities against whole M. tuberculosis cells, with MICs from 128 to 16 microg/ml. A rhodanine structural motif was present in three of the enzyme inhibitors, and two of these showed activity against whole M. tuberculosis cells. The enzyme assay was used to screen 60 Peruvian plant extracts known to inhibit the growth of M. tuberculosis in culture; two extracts were active inhibitors in the enzyme assay at concentrations of less than 2 microg/ml.

Carbohydrate Dehydrogenases↗
PubMed1976

Metabolism of L-rhamnose in Arthrobacter pyridinolis.

In Arthrobacter pyridinolis, a respiration-coupled transport system for L-rhamnose caused accumulation of free L-rhamnose, while a phosphoenolpyruvate: L-rhamnose phosphotransferase system caused accumulation of L-rhamnose I-phosphate (Levinson & Krulwich, 1974). The pathways for subsequent metabolism of L-rhamnose and L-rhamose I-phosphate have now been investigated. Arthrobacter pyridinolis contains an inducible L-rhamnose isomerase and L-rhamnulokinase, as well as a constitutive L-rhamnulose I-phosphate aldolase. Results with mutants which are unable to metabolize L-rhamnose suggest the presence of an L-rhamnose I-phosphate phosphatase, which forms free L-rhamnose by hydrolysis of L-rhamnose I-phosphate produced by the phosphotransferase system. Mutants which lack this enzyme exhibited severe inhibition of growth in the presence of L-rhamnose plus any of a variety of carbon sources. There is some evidence that this inhibition was due to accumulation of L-rhamnose I-phosphate at toxic concentrations within the bacteria. The metabolism of L-rhamnose transported by the phosphotransferase system therefore appears to occur by hydrolysis of L-rhamnose I-phosphate to free L-rhamnose by a phosphatase. Metabolism of the L-rhamnose thus produced, and of that accumulated by the respiration-coupled transport system, the proceeds by the sequence of reactions: L-rhamnose leads to L-rhamnulose leads to L=rhamnulose I-phosphate leads to dihydroxyacetone phosphate plus L-lactaldehyde.

Aldehyde-Lyases↗
PubMed1993

Proton-linked L-rhamnose transport, and its comparison with L-fucose transport in Enterobacteriaceae.

1. An alkaline pH change occurred when L-rhamnose, L-mannose or L-lyxose was added to L-rhamnose-grown energy-depleted suspensions of strains of Escherichia coli. This is diagnostic of sugar-H+ symport activity. 2. L-Rhamnose, L-mannose and L-lyxose were inducers of the sugar-H+ symport and of L-[14C]rhamnose transport activity. L-Rhamnose also induced the biochemically and genetically distinct L-fucose-H+ symport activity in strains competent for L-rhamnose metabolism. 3. Steady-state kinetic measurements showed that L-mannose and L-lyxose were competitive inhibitors (alternative substrates) for the L-rhamnose transport system, and that L-galactose and D-arabinose were competitive inhibitors (alternative substrates) for the L-fucose transport system. Additional measurements with other sugars of related structure defined the different substrate specificities of the two transport systems. 4. The relative rates of H+ symport and of sugar metabolism, and the relative values of their kinetic parameters, suggested that the physiological role of the transport activity was primarily for utilization of L-rhamnose, not for L-mannose or L-lyxose. 5. L-Rhamnose transport into subcellular vesicles of E. coli was dependent on respiration, was optimal at pH 7, and was inhibited by protonophores and ionophores. It was insensitive to N-ethylmaleimide or cytochalasin B. 6. L-Rhamnose, L-mannose and L-lyxose each elicited an alkaline pH change when added to energy-depleted suspensions of L-rhamnose-grown Salmonella typhimurium LT2, Klebsiella pneumoniae, Klebsiella aerogenes, Erwinia carotovora carotovora and Erwinia carotovora atroseptica. The relative rates of subsequent acidification varied, depending on both the organism and the sugar. L-Fucose promoted an alkaline pH change in all the L-rhamnose-induced organisms except the Erwinia species. No L-rhamnose-H+ symport occurred in any organism grown on L-fucose. 7. All these results showed that L-rhamnose transport into the micro-organisms occurred by a system different from that for L-fucose transport. Both systems are energized by the trans-membrane electrochemical gradient of protons. 8. Neither steady-state kinetic measurements nor binding-protein assays revealed the existence of a second L-rhamnose transport system in E. coli.

Binding, Competitive↗
PubMed1963

THYMIDINE DIPHOSPHATE-L-RHAMNOSE METABOLISM IN SMOOTH AND ROUGH STRAINS OF ESCHERICHIA COLI AND SALMONELLA WESLACO.

Okazaki, Tuneko (Washington University School of Medicine, St. Louis, Mo.), Jack L. Stominger, and Reiji Okazaki. Thymidine diphosphate-l-rhamnose metabolism in smooth and rough strains of Escherichia coli and Salmonella weslaco. J. Bacteriol. 86:118-124. 1963.-Logarithmic-phase cells of Escherichia coli O18, which have rhamnose in their lipopolysaccharide, contained only traces of thymidine diphosphate (TDP)-l-rhamnose. Extracts of this organism, however, catalyzed the synthesis of TDP-l-rhamnose from TDP-d-glucose. On the other hand, cells of E. coli R44, a rough variant of this strain which contains no rhamnose in its lipopolysaccharide, contained a large amount of TDP-l-rhamnose. Like the smooth form, this organism was able to synthesize TDP-l-rhamnose. The rough variant is apparently a mutant blocked in some manner in utilization of TDP-l-rhamnose for lipopolysaccharide synthesis. Similar studies of smooth (rhamnose-containing) and rough (rhamnose-lacking) forms of Salmonella weslaco showed that both organisms can synthesize TDP-l-rhamnose from TDP-d-glucose. In contrast to the smooth and rough forms of E. coli O18, only traces of TDP-l-rhamnose were detected in extracts of both forms. A second thymidine diphosphosugar compound isolated from E. coli R44 is similar or identical to TDP-X, previously isolated from E. coli Y-10.

Escherichia coli↗
PubMed2000

The structure of rhamnose isomerase from Escherichia coli and its relation with xylose isomerase illustrates a change between inter and intra-subunit complementation during evolution.

Using a new expression construct, rhamnose isomerase from Escherichia coli was purified and crystallized. The crystal structure was solved by multiple isomorphous replacement and refined to a crystallographic residual of 17.4 % at 1.6 A resolution. Rhamnose isomerase is a tight tetramer of four (beta/alpha)(8)-barrels. A comparison with other known structures reveals that rhamnose isomerase is most similar to xylose isomerase. Alignment of the sequences of the two enzymes based on their structures reveals a hitherto undetected sequence identity of 13 %, suggesting that the two enzymes evolved from a common precursor. The structure and arrangement of the (beta/alpha)(8)-barrels of rhamnose isomerase are very similar to xylose isomerase. Each enzyme does, however, have additional alpha-helical domains, which are involved in tetramer association, and largely differ in structure. The structures of complexes of rhamnose isomerase with the inhibitor l-rhamnitol and the natural substrate l-rhamnose were determined and suggest that an extended loop, which is disordered in the native enzyme, becomes ordered on substrate binding, and may exclude bulk solvent during catalysis. Unlike xylose isomerase, this loop does not extend across a subunit interface but contributes to the active site of its own subunit. It illustrates how an interconversion between inter and intra-subunit complementation can occur during evolution. In the crystal structure (although not necessarily in vivo) rhamnose isomerase appears to bind Zn(2+) at a "structural" site. In the presence of substrate the enzyme also binds Mn(2+) at a nearby "catalytic" site. An array of hydrophobic residues, not present in xylose isomerase, is likely to be responsible for the recognition of l-rhamnose as a substrate. The available structural data suggest that a metal-mediated hydride-shift mechanism, which is generally favored for xylose isomerase, is also feasible for rhamnose isomerase.

Aldose-Ketose Isomerases↗
PubMed2004

L-Rhamnose increases serum propionate after long-term supplementation, but lactulose does not raise serum acetate.

BACKGROUND: Acute ingestion of the unabsorbed sugar l-rhamnose in humans raises serum propionate, whereas acute ingestion of lactulose raises serum acetate. It is not known whether short-chain fatty acid concentrations in urine and feces reflect those in blood. OBJECTIVE: The objective was to test the effects of oral l-rhamnose and lactulose for 28 d on acetate and propionate concentrations in serum, urine, and feces. DESIGN: Eleven subjects ingested 25 g l-rhamnose, lactulose, or d-glucose (control) for 28 d in a partially randomized crossover design. One fecal sample, hourly blood samples, and all urine samples were collected over 12 h on the last day of each phase. RESULTS: The increase in serum propionate was greater after l-rhamnose than after lactulose (P < 0.05). The effect of lactulose on serum acetate was not significant, but lactulose raised the acetate:propionate ratio compared with d-glucose or l-rhamnose in serum (P < 0.005) and urine (P < 0.02). Flatulence was significantly greater after lactulose and l-rhamnose than after d-glucose (P < 0.0001), an effect that lasted 4 wk with lactulose but only 1 wk with l-rhamnose. CONCLUSIONS: This study confirmed that l-rhamnose ingestion over 28 d continues to selectively raise serum propionate in humans. Although serum acetate did not increase significantly after lactulose, the serum acetate:propionate ratio was significantly different after l-rhamnose and lactulose, which suggests that these substrates could be used to examine the role of colonic acetate and propionate production in the effect of dietary fiber on lipid metabolism. Changes in the ratio of urinary acetate to propionate reflected those in serum.

Acetates↗
PubMed1991

L-lyxose metabolism employs the L-rhamnose pathway in mutant cells of Escherichia coli adapted to grow on L-lyxose.

Escherichia coli cannot grow on L-lyxose, a pentose analog of the 6-deoxyhexose L-rhamnose, which supports the growth of this and other enteric bacteria. L-Rhamnose is metabolized in E. coli by a system that consists of a rhamnose permease, rhamnose isomerase, rhamnulose kinase, and rhamnulose-1-phosphate aldolase, which yields the degradation products dihydroxyacetone phosphate and L-lactaldehyde. This aldehyde is oxidized to L-lactate by lactaldehyde dehydrogenase. All enzymes of the rhamnose system were found to be inducible not only by L-rhamnose but also by L-lyxose. L-Lyxose competed with L-rhamnose for the rhamnose transport system, and purified rhamnose isomerase catalyzed the conversion of L-lyxose into L-xylulose. However, rhamnulose kinase did not phosphorylate L-xylulose sufficiently to support the growth of wild-type E. coli on L-lyxose. Mutants able to grow on L-lyxose were analyzed and found to have a mutated rhamnulose kinase which phosphorylated L-xylulose as efficiently as the wild-type enzyme phosphorylated L-rhamnulose. Thus, the mutated kinase, mapped in the rha locus, enabled the growth of the mutant cells on L-lyxose. The glycolaldehyde generated in the cleavage of L-xylulose 1-phosphate by the rhamnulose-1-phosphate aldolase was oxidized by lactaldehyde dehydrogenase to glycolate, a compound normally utilized by E. coli.

Acetaldehyde↗
PubMed2002

Homologs of the Rml enzymes from Salmonella enterica are responsible for dTDP-beta-L-rhamnose biosynthesis in the gram-positive thermophile Aneurinibacillus thermoaerophilus DSM 10155.

The glycan chains of the surface layer (S-layer) glycoprotein from the gram-positive, thermophilic bacterium Aneurinibacillus (formerly Bacillus) thermoaerophilus strain DSM 10155 are composed of L-rhamnose- and D-glycero-D-manno-heptose-containing disaccharide repeating units which are linked to the S-layer polypeptide via core structures that have variable lengths and novel O-glycosidic linkages. In this work we investigated the enzymes involved in the biosynthesis of thymidine diphospho-L-rhamnose (dTDP-L-rhamnose) and their specific properties. Comparable to lipopolysaccharide O-antigen biosynthesis in gram-negative bacteria, dTDP-L-rhamnose is synthesized in a four-step reaction sequence from dTTP and glucose 1-phosphate by the enzymes glucose-1-phosphate thymidylyltransferase (RmlA), dTDP-D-glucose 4,6-dehydratase (RmlB), dTDP-4-dehydrorhamnose 3,5-epimerase (RmlC), and dTDP-4-dehydrorhamnose reductase (RmlD). The rhamnose biosynthesis operon from A. thermoaerophilus DSM 10155 was sequenced, and the genes were overexpressed in Escherichia coli. Compared to purified enterobacterial Rml enzymes, the enzymes from the gram-positive strain show remarkably increased thermostability, a property which is particularly interesting for high-throughput screening and enzymatic synthesis. The closely related strain A. thermoaerophilus L420-91(T) produces D-rhamnose- and 3-acetamido-3,6-dideoxy-D-galactose-containing S-layer glycan chains. Comparison of the enzyme activity patterns in A. thermoaerophilus strains DSM 10155 and L420-91(T) for L-rhamnose and D-rhamnose biosynthesis indicated that the enzymes are differentially expressed during S-layer glycan biosynthesis and that A. thermoaerophilus L420-91(T) is not able to synthesize dTDP-L-rhamnose. These findings confirm that in each strain the enzymes act specifically on S-layer glycoprotein glycan formation.

Bacterial Proteins↗
PubMed2006

Functional analysis of Arabidopsis thaliana RHM2/MUM4, a multidomain protein involved in UDP-D-glucose to UDP-L-rhamnose conversion.

UDP-L-rhamnose is required for the biosynthesis of cell wall rhamnogalacturonan-I, rhamnogalacturonan-II, and natural compounds in plants. It has been suggested that the RHM2/MUM4 gene is involved in conversion of UDP-D-glucose to UDP-L-rhamnose on the basis of its effect on rhamnogalacturonan-I-directed development in Arabidopsis thaliana. RHM2/MUM4-related genes, RHM1 and RHM3, can be found in the A. thaliana genome. Here we present direct evidence that all three RHM proteins have UDP-D-glucose 4,6-dehydratase, UDP-4-keto-6-deoxy-D-glucose 3,5-epimerase, and UDP-4-keto-L-rhamnose 4-keto-reductase activities in the cytoplasm when expressed in the yeast Saccharomyces cerevisiae. Functional domain analysis revealed that the N-terminal region of RHM2 (RHM2-N; amino acids 1-370) has the first activity and the C-terminal region of RHM2 (RHM2-C; amino acids 371-667) has the two following activities. This suggests that RHM2 converts UDP-d-glucose to UDP-L-rhamnose via an UDP-4-keto-6-deoxy-D-glucose intermediate. Site-directed mutagenesis of RHM2 revealed that mucilage defects in MUM4-1 and MUM4-2 mutant seeds of A. thaliana are caused by abolishment of RHM2 enzymatic activity in the mutant strains and furthermore, that the GXXGXX(G/A) and YXXXK motifs are important for enzymatic activity. Moreover, a kinetic analysis of purified His(6)-tagged RHM2-N protein revealed 5.9-fold higher affinity of RHM2 for UDP-D-glucose than for dTDP-D-glucose, the preferred substrate for dTDP-D-glucose 4,6-dehydratase from bacteria. RHM2-N activity is strongly inhibited by UDP-L-rhamnose, UDP-D-xylose, and UDP but not by other sugar nucleotides, suggesting that RHM2 maintains cytoplasmic levels of UDP-D-glucose and UDP-L-rhamnose via feedback inhibition by UDP-L-rhamnose and UDP-D-xylose.

Amino Acid Motifs↗