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PubMed1996

Structural analysis of monosaccharide recognition by rat liver mannose-binding protein.

The structural basis of carbohydrate recognition by rat liver mannose-binding protein (MBP-C) has been explored by determining the three-dimensional structure of the C-type carbohydrate-recognition domain (CRD) of MBP-C using x-ray crystallography. The structure was solved by molecular replacement using rat serum mannose-binding protein (MBP-A) as a search model and was refined to maximum Bragg spacings of 1.7 A. Despite their almost identical folds, the dimeric structures formed by the two MBP CRDs differ dramatically. Complexes of MBP-C with methyl glycosides of mannose, N-acetylglucosamine, and fucose were prepared by soaking MBP-C crystals in solutions containing these sugars. Surprisingly, the pyranose ring of mannose is rotated 180 degrees relative to the orientation observed previously in MBP-A, but the local interactions between sugar and protein are preserved. For each of the bound sugars, vicinal, equatorial hydroxyl groups equivalent to the 3- and 4-OH groups of mannose directly coordinate Ca2+ and form hydrogen bonds with residues also serving as Ca2+ ligands. Few interactions are observed between other parts of the sugar and the protein. A complex formed between free galactose and MBP-C reveals a similar mode of binding, with the anomeric hydroxyl group serving as one of the Ca2+ ligands. A second binding site for mannose has also been observed in one of two copies in the asymmetric unit at a sugar concentration of 1.3 M. These structures explain how MBPs recognize a wide range of monosaccharides and suggest how fine specificity differences between MBP-A and MBP-C may be achieved.

Amino Acid Sequence↗
PubMed1996

Thermodynamics of monosaccharide and disaccharide binding to Erythrina corallodendron lectin.

Isothermal titration calorimetry measurements of the binding of 2'-fucosyllactose, lactose, N-acetyllactosamine, galactopyranose, 2-acetamido-2-deoxygalactopyranoside, methyl alpha-N-dansylgalactosaminide (Me-alpha-DNS-GalN), methyl alpha-D-galactopyranoside, methyl beta-D-galactopyranoside, and fucose to Erythrina corallodendron lectin (ECorL), a dimer with one binding site per subunit, were performed at 283-286 and 297-299 K. The site binding enthalpies, DeltaHb, with the exception of Me-alpha-DNS-GalN, are the same at both temperatures and range from -47.1 +/- 1.0 kJ mol-1 for N-acetyllactosamine to -4.4 +/- 0.3 kJ mol-1 for fucose, and the site binding constants range from 3.82 +/- 0.9 x 10(5)M-1 for Me-alpha-DNS-GalN at 283.2 K to 0.46 +/- 0.05 x 10(3) M-1 for fucose at 297.2 K. The binding reactions are mainly enthalpically driven except for fucose and exhibit enthalpy-entropy compensation. The binding enthalpies of the disaccharides are about twice the binding enthalpies of the monosaccharides in contrast to concanavalin A where the binding enthalpies do not double for the disaccharides. Differential scanning calorimetry measurements show that denaturation of the ECorL dimer results in dissociation into its monomer subunits. The binding constants from the increase in denaturation temperature of ECorL in the presence of saccharides are in agreement with values from isothermal titration calorimetry results. The thermal denaturation of ECorL occurs around 333 K, well below the 344-360 K denaturation temperature of other legume lectins of similar size and tertiary structure, undoubtedly due to the difference in its quaternary structure relative to other legume lectins. This is also apparent from the independent unfolding of its two domains.

Binding Sites↗
PubMed1997

Mechanism of Ca2+ and monosaccharide binding to a C-type carbohydrate-recognition domain of the macrophage mannose receptor.

Site-directed mutagenesis has been used to identify residues that ligate Ca2+ and sugar to the fourth C-type carbohydrate-recognition domain (CRD) of the macrophage mannose receptor. CRD-4 is the only one of the eight CRDs of the mannose receptor to exhibit detectable monosaccharide binding when expressed in isolation, and it is central to ligand binding by the receptor. CRD-4 requires two Ca2+ for sugar binding, like the CRD of rat serum mannose-binding protein (MBP-A). Sequence comparisons between the two CRDs suggest that the binding site for one Ca2+, which ligates directly to the bound sugar in MBP-A, is conserved in CRD-4 but that the auxiliary Ca2+ binding site is not. Mutation of the four residues at positions in CRD-4 equivalent to the auxiliary Ca2+ binding site in MBP-A indicates that only one, Asn728, is involved in ligation of Ca2+. Alanine-scanning mutagenesis was used to identify two other asparagine residues and one glutamic acid residue that are probably involved in ligation of the auxiliary Ca2+ to CRD-4. Sequence comparisons with other C-type CRDs suggest that the proposed binding site for the auxiliary Ca2+ in CRD-4 of the mannose receptor is unique. Evidence that the conserved Ca2+ in CRD-4 bridges between the protein and bound sugar in a manner analogous to MBP-A was obtained by mutation of one of the amino acid side chains at this site. Ring current shifts seen in the 1H NMR spectra of methyl glycosides of mannose, GlcNAc, and fucose in the presence of CRD-4 and site-directed mutagenesis indicate that a stacking interaction with Tyr729 is also involved in binding of sugars to CRD-4. This interaction contributes about 25% of the total free energy of binding to mannose. C-5 and C-6 of mannose interact with Tyr729, whereas C-2 of GlcNAc is closest to this residue, indicating that these two sugars bind to CRD-4 in opposite orientations. Sequence comparisons with other mannose/GlcNAc-specific C-type CRDs suggest that use of a stacking interaction in the binding of these sugars is probably unique to CRD-4 of the mannose receptor.

Alanine↗
PubMed1967

Evidence for carrier-mediated transport of monosaccharides in the Ehrlich ascites tumor cell.

Evidence for carrier-mediated transport of monosaccharides in the Ehrlich ascites tumor cells was provided through kinetic analysis of data obtained by: (a) studying sugar uptake by dilute cell suspensions with an optical densimetric apparatus, (b) studying sugar uptake by thicker cell suspensions by means of direct chemical analytical methods using packed cell plugs, (c) observing the effects of a competitive inhibitor upon sugar uptake with the chemical analytical method, and (d) measurement of tracer uptake of a high affinity sugar in thick cell suspensions in the absence of net movement. Quantitative application of the data obtained with the above experimental procedures to theoretical model systems derived for both carrier-mediated transport and simple passive diffusion indicated that the results were consonant with predictions for the carrier-mediated transport model, but could not be explained on the basis of uncomplicated diffusion.

Animals↗
PubMed2001

Requirement of the Lec35 gene for all known classes of monosaccharide-P-dolichol-dependent glycosyltransferase reactions in mammals.

The Lec35 gene product (Lec35p) is required for utilization of the mannose donor mannose-P-dolichol (MPD) in synthesis of both lipid-linked oligosaccharides (LLOs) and glycosylphosphatidylinositols, which are important for functions such as protein folding and membrane anchoring, respectively. The hamster Lec35 gene is shown to encode the previously identified cDNA SL15, which corrects the Lec35 mutant phenotype and predicts a novel endoplasmic reticulum membrane protein. The mutant hamster alleles Lec35.1 and Lec35.2 are characterized, and the human Lec35 gene (mannose-P-dolichol utilization defect 1) was mapped to 17p12-13. To determine whether Lec35p was required only for MPD-dependent mannosylation of LLO and glycosylphosphatidylinositol intermediates, two additional lipid-mediated reactions were investigated: MPD-dependent C-mannosylation of tryptophanyl residues, and glucose-P-dolichol (GPD)-dependent glucosylation of LLO. Both were found to require Lec35p. In addition, the SL15-encoded protein was selective for MPD compared with GPD, suggesting that an additional GPD-selective Lec35 gene product remains to be identified. The predicted amino acid sequence of Lec35p does not suggest an obvious function or mechanism. By testing the water-soluble MPD analog mannose-beta-1-P-citronellol in an in vitro system in which the MPD utilization defect was preserved by permeabilization with streptolysin-O, it was determined that Lec35p is not directly required for the enzymatic transfer of mannose from the donor to the acceptor substrate. These results show that Lec35p has an essential role for all known classes of monosaccharide-P-dolichol-dependent reactions in mammals. The in vitro data suggest that Lec35p controls an aspect of MPD orientation in the endoplasmic reticulum membrane that is crucial for its activity as a donor substrate.

Acyclic Monoterpenes↗
PubMed2003

Roles of cell-wall invertases and monosaccharide transporters in the growth and development of Arabidopsis.

The hydrolysis of sucrose by cell-wall invertases (cwINV) and the subsequent import of hexoses into target cells appears to be crucial for appropriate metabolism, growth and differentiation in plants. Hexose uptake from the apoplast is catalysed by monosaccharide/H+ symporters (Sugar Transport Proteins or STPs), which have the potential to sense sugars. Import of extracellular hexoses may generate signals to orchestrate cellular activities, or simply feed metabolic pathways distinct from those fed by sucrose. It is predicted that Arabidopsis has six cwINV genes and at least 14 STP genes. These genes show different spatial and temporal patterns of expression, and several knock-out mutants have been isolated for analysis. AtSTP1 transports glucose, galactose, xylose, and mannose, but not fructose. It accounts for the majority of the AtSTP activity in vegetative tissues and its activity is markedly repressed by treatment with exogenous sugars. These observations are consistent with a role in the retrieval of cell-wall-derived sugars, for example, during carbohydrate limitation or cell expansion. The AtSTP1 gene is also expressed in developing seeds, where it might be responsible for the uptake of glucose derived from imported sucrose. The large number of AtcwINV and AtSTP genes, together with complex patterns of expression for each, and the possibility that each protein may have more than one physiological function, provides the plant with the potential for a multiplicity of patterns of monosaccharide utilization to direct growth and differentiation or to respond flexibly to changing environmental conditions.

Arabidopsis↗
PubMed1991

The mutagenicity of azido derivatives of monosaccharides and alcohols and of N-(3-azido-2-hydroxypropyl) derivatives of purines and pyrimidines in Arabidopsis thaliana and in Salmonella typhimurium.

The azido derivatives of alcohols (3-azido-1,2-propandiol and 1,3-diazido-2-propanol) and monosaccharides (6-azido-6-deoxy-beta-D-glucose and 6-azido-6-deoxy-beta-D-galactose), as well as the proximal mutagenic product of sodium azide metabolism beta-azido-L-alanine, exhibited a high mutagenic activity in a higher plant Arabidopsis thaliana and in Salmonella typhimurium. In contrast, 11 N-(3-azido-2-hydroxypropyl) derivatives of purines and pyrimidines (adenine, thymine, uracil, cytosine, 2-amino-6-chloropurine, 6-chloropurine, 2,6-diaminopurine, 6-methylthiopurine, 4-O-methylthymine, 4-O-methyluracil and 7-deaza-8-azaadenine) were mutagenic in the Ames assay but ineffective in the Arabidopsis mutagenicity assay.

1-Propanol↗
PubMed1989

Acquired monosaccharide intolerance in infants.

To determine the frequency with which acquired monosaccharide intolerance (AMI) occurs in infants less than 3 months of age, we performed a prospective descriptive study of infants admitted to the hospital for diarrhea. We searched for differences between the characteristics and causes of AMI in these infants and those of a cohort of similar-aged infants admitted with acute diarrhea (AD). Five hundred fifty-five infants less than 3 months of age admitted with diarrhea were enrolled. Nine percent of those infants had AMI, 40% had other forms of chronic diarrhea, and 51% had AD. The mean age at hospital admission was 32 days for the infants with AMI and 44 days for the infants with AD. The mean weight loss of AMI infants was 0.3 g/day since birth, and the mean weight gain was 14.3 g/day for AD infants. The mean dehydration by difference in weights at admission and 48 h postadmission was 5% for AMI and 3% for AD infants. Bacterial and viral causes of the diarrhea were similar. At admission to the hospital, infants in whom AMI subsequently developed were younger, more malnourished, had more prolonged diarrhea, and were more dehydrated than the AD infants. Malnutrition stands out as a significant antecedent factor that contributes to the development of AMI.

Acute Disease↗
PubMed1989

Dietary origin of retained H+ in infants with acquired monosaccharide intolerance.

Net external acid balance was studied in 12 malnourished infants with chronic diarrhea (some of whom had acquired monosaccharide intolerance). When the infants achieved an adequate energy intake from a formula that contained either glucose or glucose polymers, seven developed metabolic acidosis and five remained free of acidosis. During the study, the acidotic infants produced a significant excess of acid (3.7 +/- 2 vs. 0.5 +/- 2 mEq/kg/day, p less than 0.005). The amount they excreted in urine (2.9 +/- 2 mEq/kg/day), however, was similar to that excreted by nonacidotic infants (2.7 +/- 2 mEq/kg/day) and indicated renal inability to reduce the excess acid load. The net effect was hydrogen ion (H+) retention (+0.8 +/- 0.8 vs. -2.2 +/- 0.8 mEq/kg/day, p less than 0.001). Good correlation existed between the net acid balance and the acid-base measurement in the blood. We speculate that (a) the increased acid load was a consequence of colonic bacterial production of volatile fatty acids from carbohydrate malabsorbed from the small bowel and (b) the renal incapacity to excrete H+ probably was secondary to potassium and phosphate depletion.

Acidosis↗
PubMed1980

The growth of Moniliformis (Acanthocephala) in rats fed on various monosaccharides and disaccharides.

Aspects of the course of infection, growth and reproductive activity of Moniliformis were studied in adult male and female rats fed on isoenergetic purified diets containing various sugars. When rats were infected and fed on experimental diets containing either 3% glucose or 3% galactose for 5 weeks, very little growth of worms and no signs of reproduction were observed. In contrast, Moniliformis grew well and showed many signs of normal reproduction when the rats were fed on diets containing either 3% fructose or 3% mannose. The ability of the worms to grow and reproduce was not lost by maintaining them first for 5 weeks in rats fed on diets containing 3% glucose and 3% galactose. When the diets of such rats were changed to ones containing 3% starch and 3% fructose, respectively, for a further 5 weeks, the worms grew and normal reproduction occurred. Similar experiments were carried out in which groups of infected rats were fed for 5 weeks on diets containing gradually increasing amounts of glucose (6-36%). It was not until the rats were fed on diets containing 24% glucose that the mean dry mass of the worms approached that of worms from rats fed on the diet containing 3% fructose; no host diet was found to be as effective a supporter of worm growth as 3% mannose. Under no circumstances, not even when the host's diet contained 36%, was galactose found to be a suitable sugar for supporting the growth and reproduction of Moniliformis. Results consistent with those recorded for worms from rats fed on the diets containing monosaccharides were obtained when infected rats were fed for 5 weeks on diets containing 3% of various disaccharides. Considerable growth and reproduction of Moniliformis occurred when sucrose was included in the host's diet, but not when lactose, maltose or trehalose was present. Several of these observations may be related to the fact that different sugars are absorbed at different rates from the intestinal tract. It is suggested that all of a given sugar, when present in the diet at a low concentration, may be removed rapidly from the anterior part of the small intestine with the result that none will be available to the parasites. Significant amounts, however, of those sugars that are absorbed more slowly may reach the region of the intestine in which the parasite normally lives.

Acanthocephala↗
PubMed2003

AtSTP6, a new pollen-specific H+-monosaccharide symporter from Arabidopsis.

This paper describes the molecular, kinetic, and physiological characterization of AtSTP6, a new member of the Arabidopsis H(+)/monosaccharide transporter family. The AtSTP6 gene (At3g05960) is interrupted by two introns and encodes a protein of 507 amino acids containing 12 putative transmembrane helices. Expression in yeast (Saccharomyces cerevisiae) shows that AtSTP6 is a high-affinity (K(m) = 20 microM), broad-spectrum, and uncoupler-sensitive monosaccharide transporter that is targeted to the plasma membrane and that can complement a growth deficiency resulting from the disruption of most yeast hexose transporter genes. Analyses of AtSTP6-promoter::GUS plants and in situ hybridization experiments detected AtSTP6 expression only during the late stages of pollen development. A transposon-tagged Arabidopsis mutant was isolated and homozygous plants were analyzed for potential effects of the Atstp6 mutation on pollen viability, pollen germination, fertilization, and seed production. However, differences between wild-type and mutant plants could not be observed.

Arabidopsis↗
PubMed2003

The monosaccharide transporter gene, AtSTP4, and the cell-wall invertase, Atbetafruct1, are induced in Arabidopsis during infection with the fungal biotroph Erysiphe cichoracearum.

Powdery mildew fungi are biotrophic pathogens that form a complex interface, the haustorium, between the host plant and the parasite. The pathogen acts as an additional sink, competing with host sinks, resulting in considerable modification of photoassimilate production and partitioning within the host tissue. Here, we examine the factors that may contribute to these changes. We show for the first time in one biotrophic interaction (Arabidopsis/Erysiphe cichoracearum) all of the following responses: Glc uptake in host tissues is enhanced after fungal infection; this coincides with the induction of expression of the monosaccharide transporter gene, Arabidopsis sugar transport protein 4 (AtSTP4), in infected leaves; invertase activity and transcript levels for a cell wall invertase, Atbetafruct1, increase substantially in Arabidopsis during attack by this pathogen. Before infection, Arabidopsis plants transformed with an AtSTP4 promoter-beta-glucuronidase construct show expression mainly in sink tissues such as roots; after infection, AtSTP4 expression is induced in the mature leaves and increases over the 6-d time period. Sections of infected leaves stained for beta-glucuronidase show that AtSTP4 expression is not confined to infected epidermal cells but is also evident in a wider range of cells, including those of the vascular tissue. The results are discussed in relation to the possible coordinated expression of hexose transporters and cell wall invertase in the host response to powdery mildew infection.

4-Chloromercuribenzenesulfonate↗
PubMed2004

Arabidopsis POLYOL TRANSPORTER5, a new member of the monosaccharide transporter-like superfamily, mediates H+-Symport of numerous substrates, including myo-inositol, glycerol, and ribose.

Six genes of the Arabidopsis thaliana monosaccharide transporter-like (MST-like) superfamily share significant homology with polyol transporter genes previously identified in plants translocating polyols (mannitol or sorbitol) in their phloem (celery [Apium graveolens], common plantain [Plantago major], or sour cherry [Prunus cerasus]). The physiological role and the functional properties of this group of proteins were unclear in Arabidopsis, which translocates sucrose and small amounts of raffinose rather than polyols. Here, we describe POLYOL TRANSPORTER5 (AtPLT5), the first member of this subgroup of Arabidopsis MST-like transporters. Transient expression of an AtPLT5-green fluorescent protein fusion in plant cells and functional analyses of the AtPLT5 protein in yeast and Xenopus oocytes demonstrate that AtPLT5 is located in the plasma membrane and characterize this protein as a broad-spectrum H+-symporter for linear polyols, such as sorbitol, xylitol, erythritol, or glycerol. Unexpectedly, however, AtPLT5 catalyzes also the transport of the cyclic polyol myo-inositol and of different hexoses and pentoses, including ribose, a sugar that is not transported by any of the previously characterized plant sugar transporters. RT-PCR analyses and AtPLT5 promoter-reporter gene plants revealed that AtPLT5 is most strongly expressed in Arabidopsis roots, but also in the vascular tissue of leaves and in specific floral organs. The potential physiological role of AtPLT5 is discussed.

Animals↗
PubMed1983

Monosaccharides bound to hemoglobins in normal and diabetic individuals. Evidence for glucose, mannose and galactose as sugars released by methanolysis of the different hemoglobin components.

Direct evidence is given for the presence of glucose, mannose and galactose as the products of hydrolysis of hemoglobins A1a1, A1a2, A1b, A1c and A0. The presence of galactose cannot be explained by the earlier hypothesis of Amadori rearrangement and suggests the existence of further complex rearrangements. Monosaccharide content of the different hemoglobin components varies from 0.2-2.0 mol/mol of alpha beta dimer with an increase of 1.5-2.0-times in diabetic components. This increase is not accompanied by net charge differences, suggesting that additionally bound sugars are not responsible for the pI modification of these hemoglobins. The pattern of glucose, mannose and galactose ratio in normal individuals divides these hemoglobins into two classes, hemoglobins A1b, A1c and A0 (ratio 0.60:0.25:0.15) on one hand and hemoglobins A1a1 and A1a2 (ratio 0.40:0.40: 0.20) on the other. These findings suggest that diverse mechanisms for sugar binding might exist between these two classes of glycosylated hemoglobins. This difference disappears in diabetic components suggesting that the non-NH2-terminal sites are glycosylated in all components by a common mechanism. Increase in glucose at the expense of mannose and galactose, as observed in diabetics, could be an indicator of recent glycosylation.

Blood Glucose↗
PubMed1982

Inhibition of secondary IgG responses by monosaccharides: evidence for I-region control.

Certain monosaccharides selectively inhibit secondary IgG responses in vitro. Genetic analyses described in this report revealed that the inhibitory sugars differed between mouse strains and these differences mapped to the I-J and I-C subregions of the murine MHC. These results imply that interaction between T and B lymphocytes can involve the recognition of I-region controlled carbohydrate structures.

Acetylgalactosamine↗
PubMed1975

Pancreatic islet cells: effects of monosaccharides, glycolytic intermediates and metabolic inhibitors on membrane potential and electrical activity.

1. The effects of monosaccharides, glycolytic intermediates, metabolic inhibitors and anxia, have been studied on the membrane electrical activity of mouse pancreatic islet cells in vitro using a single intracellular micro-electrode for both voltage recording and current injection. 2. In addition to D-glucose (28mM), D-mannose (16-6mM), and L-leucin (10mM), the substances D-glyceraldehyde (11mM), and acetoacetate (20 mM), induced action potentials in islet cells but other glucos analogues and metabolic intermediates including L-glucose dod not. 3. Mannoheptulose 20 mM), but not D-galactose or 2-deoxy-D-glucose, antagonized the electrical activity induced in islet cells by D-glucose, 28mM. Prior treatment of the cells with mannoheptulose caused them to hyperpolarize and completely prevented the appearance of electrical activity on subsequent exposure to D-glucose. 4. Electrical activity induced by D0glucose 28mM, was progressively inhibited by phloridzin, 10mM, if the cells were exposed to D-glucose and inhibitor simultaneously, and abolished on pretreatment with inhibitor for 30-60 min. Phloridzin also caused depolarization of the islet cells which was independent of extracellular glucose. 5. Anoxia completely blocked the electrical activity induced by glucose but not that evoked by D-glyceraldehyde, L-leucine, tolbutamide or glibenclamide. 6. Iodoacetic acid, 5 mM, rapidly blocked glucose-induced electrical activity whilst that elicited by tolbutamide was relatively resistant to inhibition. 7. The nature and possible location of the glucoreceptor in pancreatic islet cells is discussed in relation to the origin and functional significance of glucose-induced electrical activity and insulin secretion.

Acetoacetates↗
PubMed1972

The effects of different bile salts on the absorption of fluid, electrolytes, and monosaccharides in the small intestine of the rat in vivo.

The effects of different bile salts on the absorption of fluid, electrolytes, and monosaccharides have been investigated in the rat small intestine in vivo. In the jejunum, deoxycholate (1 mM) impaired absorption of water and potassium, but not of sodium or glucose; at higher concentrations (2.5 and 5 mM) secretion of fluid and electrolytes occurred, and glucose and fructose absorption was impaired. By contrast, in the ileum, 1 mM deoxycholate failed to inhibit fluid and electrolyte absorption, and a concentration of 10 mM was required completely to inhibit absorption; secretion was not observed in the ileum. Chenodeoxycholate (5 mM) produced a similar effect to deoxycholate on fluid and electrolyte absorption in both jejunum and ileum, but taurocholate (5 mM) and taurodeoxycholate (5 mM) were ineffective.In jejunum, cholate, taurocholate, and taurodeoxycholate, each at a concentration of 5 mM, were less effective inhibitors of glucose transport than deoxycholate; chenodeoxycholate failed to inhibit glucose absorption. Deoxycholate produced histological damage at 5 mM, but not at lower concentrations. The functional and structural abnormalities were shown to be reversible phenomena. These findings may be relevant to the pathogenesis of diarrhoea in patients with bacterial overgrowth in the small intestine.

Animals↗
PubMed1984

Facilitated diffusion of monosaccharides in smooth muscle of rat vas deferens in vitro.

The suitability of rat vas deferens for investigating sugar transport in smooth muscle was determined in vitro, with the nonmetabolized glucose analog 3-O-methyl-D-glucose as test sugar. Vas deferens smooth muscle contains a facilitated diffusion system for monosaccharides, as shown by saturation of the transport sites and by competition between 3-O-methyl-D-glucose and D-glucose. The activity of the facilitated diffusion system could be enhanced by hyperosmolarity and by contractile activity, but frequency dependency could not be established. A high concentration of insulin (100 mU/mL) was required to stimulate sugar transport. As smooth muscle is not a primary tissue for the storage of energy reserves, it does not require large numbers of insulin receptors.

Animals↗