In vitro and in silico inhibitory validation of Tapinanthus cordifolius leaf extract on alpha-glucosidase in the management of type 2 diabetes

The anti-diabetic properties of medicinal plants are becoming more widely recognized. To identify potential anti-diabetic agents for diabetes drug discovery, the current study used in vitro and in silico approaches to assess the alpha glucosidase inhibitory activities of Tapinanthus cordifolius (TC) leaf extracts and its bioactive components respectively. In vitro alpha glucosidase inhibitory assay was carried out on TC extract and fractions at various concentrations (50-1600 µg/mL), and the compounds with alpha glucosidase inhibitory potentials were identified using molecular docking, pharmacophore modelling, and molecular dynamics simulation. The crude extract exhibited the highest activity with an IC50 value of 248 μg/mL. Out of the 42 phytocompounds of the extract, α-Tocopherol-β-d-mannoside gave the lowest binding energy of -6.20 Kcal/mol followed by, 5-Ergosterol (-5.46 kcal/mol), Acetosyringone (-4.76 kcal/mol), and Benzaldehyde, 4-(Ethylthio)-2,5-Dimethoxy-(-4.67 kcal/mol). The selected compounds interacted with critical active site amino acid residues of alpha-glucosidase, just like the reference ligand. Molecular dynamics simulation revealed the formation of a stable complex between α-glucosidase and α-Tocopherol-β-d-mannoside, with ASP 564 sustaining two hydrogen bond connections for 99.9 and 75.0% of the simulation duration, respectively. Therefore, the selected TC compounds, especially α-Tocopherol-β-d-mannoside might be explored for future research and development as diabetic medicines.Communicated by Ramaswamy H. Sarma.

Chemical approaches for the stereocontrolled synthesis of 1,2-cis-β-D-rhamnosides

In carbohydrate chemistry, the stereoselective synthesis of 1,2-cis-glycosides remains a formidable challenge. This complexity is comparable to the synthesis of 1,2-cis-β-D-mannosides, primarily due to the adverse anomeric and Δ-2 effects. Over the past decades, to attain β-stereoselectivity in D-rhamnosylation, researchers have devised numerous direct and indirect methodologies, including the hydrogen-bond-mediated aglycone delivery (HAD) method, the synthesis of β-D-mannoside paired with C6 deoxygenation, and the combined approach of 1,2-trans-glycosylation and C2 epimerization. This review elaborates on the advancements in β-D-rhamnosylation and its implications for the total synthesis of tiacumicin B and other physiologically relevant glycans.

Fimbria targeting superparamagnetic iron oxide nanoparticles enhance the antimicrobial and antibiofilm activity of ciprofloxacin against quinolone-resistant E. coli

High quinolone resistance of Escherichia coli limits the therapy options for urinary tract infection (UTI). In response to the urgent need for efficient treatment of multidrug-resistant infections, we designed a fimbriae targeting superparamagnetic iron oxide nanoparticle (SPION) delivering ciprofloxacin to ciprofloxacin-resistant E. coli. Bovine serum albumin (BSA) conjugated poly(acrylic acid) (PAA) coated SPIONs (BSA@PAA@SPION) were developed for encapsulation of ciprofloxacin and the nanoparticles were tagged with 4-aminophenyl-α-D-mannopyrannoside (mannoside, Man) to target E. coli fimbriae. Ciprofloxacin-loaded mannoside tagged nanoparticles (Cip-Man-BSA@PAA@SPION) provided high antibacterial activity (97.1 and 97.5%, respectively) with a dose of 32 μg/mL ciprofloxacin against two ciprofloxacin-resistant E. coli isolates. Furthermore, a strong biofilm inhibition (86.9% and 98.5%, respectively) was achieved in the isolates at a dose 16 and 8 times lower than the minimum biofilm eradication concentration (MBEC) of ciprofloxacin. Weaker growth inhibition was observed with untargeted nanoparticles, Cip-BSA@PAA@SPIONs, confirming that targeting E. coli fimbria with mannoside-tagged nanoparticles increases the ciprofloxacin efficiency to treat ciprofloxacin-resistant E. coli. Enhanced killing activity against ciprofloxacin-resistant E. coli planktonic cells and strong growth inhibition of their biofilms suggest that Cip-Man-BSA@PAA@SPION system might be an alternative and/or complementary therapeutic option for the treatment of quinolone-resistant E. coli infections.

Recent Progress in 1,2-cis glycosylation for Glucan Synthesis

Controlling the stereoselectivity of 1,2-cis glycosylation is one of the most challenging tasks in the chemical synthesis of glycans. There are various 1,2-cis glycosides in nature, such as α-glucoside and β-mannoside in glycoproteins, glycolipids, proteoglycans, microbial polysaccharides, and bioactive natural products. In the structure of polysaccharides such as α-glucan, 1,2-cis α-glucosides were found to be the major linkage between the glucopyranosides. Various regioisomeric linkages, 1→3, 1→4, and 1→6 for the backbone structure, and 1→2/3/4/6 for branching in the polysaccharide as well as in the oligosaccharides were identified. To achieve highly stereoselective 1,2-cis glycosylation, including α-glucosylation, a number of strategies using inter- and intra-molecular methodologies have been explored. Recently, Zn salt-mediated cis glycosylation has been developed and applied to the synthesis of various 1,2-cis linkages, such as α-glucoside and β-mannoside, via the 1,2-cis glycosylation pathway and β-galactoside 1,4/6-cis induction. Furthermore, the synthesis of various structures of α-glucans has been achieved using the recent progressive stereoselective 1,2-cis glycosylation reactions. In this review, recent advances in stereoselective 1,2-cis glycosylation, particularly focused on α-glucosylation, and their applications in the construction of linear and branched α-glucans are summarized.

Synthesis of 2-Amino-2-deoxy-β-d-mannosides via Stereoselective Anomeric O-Alkylation of 2N,3O-Oxazolidinone-Protected d-Mannosamine: Synthesis of the Trisaccharide Repeating Unit of Streptococcus pneumoniae 19F Polysaccharide

Cesium carbonate-mediated stereoselective anomeric O-alkylation of a 2N,3O-oxazolidinone-protected d-mannosamine with sugar-derived primary or secondary alkyl triflates afforded the corresponding 2-amino-2-deoxy-β-d-mannosides in moderate to good yields and excellent stereoselectivity. The oxazolidinone ring can be opened with aqueous alkali hydroxide to liberate the amine functionality. This method has been successfully applied to the synthesis of the trisaccharide repeating unit of Streptococcus pneumoniae 19F polysaccharide.

Glyco-dependent nuclear import of glycoproteins, glycoplexes and glycosylated plasmids

This short review deals with some properties of nuclear sugar-binding proteins also called nuclear lectins, the sugar-dependent nuclear import of neoglycoproteins and the attempts of using this pathway to enhance the nuclear import of plasmids in order to hopefully increase the expression of transferred genes.

Capillary affinophoresis of pea lectin with polyliganded affinophores: a model study of divalent-polyvalent interactions

Affinophoresis is a type of affinity electrophoresis using an affinophore, a soluble ionic carrier bearing affinity ligand(s). It was reported previously that an affinophore, prepared by coupling multiple p-aminophenyl alpha-D-mannoside ligands to a part of the carboxyl groups of succinylated polylysine, specifically changed the mobility of pea lectin in agarose gel. The affinophoresis of this divalent lectin with the polyliganded affinophore was investigated by using capillary electrophoresis. Analysis of the mobility change of the lectin in the presence of differently modified affinophores showed that the affinity was larger for affinophores having higher ligand density. Analysis of the inhibition of the mobility change by a neutral ligand, with a known affinity constant for the lectin, allowed estimation of the contributions of monovalent and divalent interactions to the binding in the lectin-affinophore complex. The proportion of divalent complexes was greater for affinophores having higher ligand density. This approach to estimate the contribution of divalency in complex formation should be generally applicable to the analysis of divalent interactions with different techniques other than electrophoresis.

A liposome-based model system for the simulation of lectin-induced cell adhesion

A parallel plate flow chamber with defined wall shear rates was developed in order to study and simulate cellular adhesion to biological membranes as mediated by lectin/carbohydrate interactions. Planar bilayers containing clustered areas of various long-chain alkyl mannosides as carbohydrate ligands and supported on transparent materials were used as model membranes. Their interaction with liposomes bearing Concanavalin A as model cells was observed fluorimetrically by confocal laser scanning microscopy. The use of supported membranes made it possible to study the dependence of adhesion upon different physicochemical parameters of membranes. The liposomes of this model were able to simulate the lectin-mediated adhesion of cells in a shear flow. Once specific receptor-mediated adhesion had taken place, liposomes tended to attach irreversibly to the membrane. This could be avoided by employing lipid compositions which represent a special balance between charged and polyethylene glycol-coupled lipids. This is discussed in term of the interplay between the various attractive and repulsive forces at membrane surfaces. The dependence of liposome adhesion upon the shear rate could be detected. These results were used to evaluate binding forces between lectin-bearing liposomes and ligand-containing planar bilayers.

Difference in binding-site architecture of the serum-type and liver-type mannose-binding proteins

The carbohydrate-recognition domains (CRDs) of the serum-type and the liver-type mannose-binding proteins (MBPs) from rat display different binding characteristics toward mannose-rich oligosaccharides derived from N-glycosides, despite the overall similarity in their binding site architecture, oligomeric status and actual binding specificity at the monosaccharide level. We found that the liver-type MBP CRD of rat (MBP-C) bound methyl glycosides of certain mannobioses and -trioses, which are part of the mannose-rich N-glycoside, more tightly than methyl alpha-mannopyranoside. In contrast, the serum-type MBP CRD of rat (MBP-A) bound all the methyl glycosides of manno-oligosaccharide and methyl alpha-mannopyranoside with similar affinities. The mannobiose and -triose most strongly bound to MBP-C CRD were Man alpha (1-2)Man alpha-OMe and Man alpha (1-2)Man alpha (1-6)Man alpha-OMe, respectively. From these and other data, we postulate that the binding site of MBP-C has an extended area of interaction, probably the size of a mannotriose, while MBP-A interacts essentially with one mannose residue.

Size-dependent release of carboxyfluorescein from cetylmannoside-modified liposomes in human plasma

The interaction of liposomes with human plasma was investigated using 6(5)-carboxyfluorescein (CF) as an aqueous phase marker of cetylmannoside-modified multilamellar vesicles (Man-MLVs) of various sizes. The release of CF decreased with increasing liposome concentration. The time courses of the CF release from Man-MLVs were monitored continuously and were analysed kinetically. The curves were characterized by two phases, the first-order release process and the maximum release, which represent the rate and the extent of CF release, respectively. The increase of liposome size increased the rate of release by 42% and the extent of release by 121%, respectively. These effects of liposome size on the release processes were suggested to result from the size-dependent affinities of liposomes to the human complement system. The assay system of liposomally bound fragments of complement component 3 (C3), such as C3b and/or iC3b, was developed by applying a sandwich enzyme-linked immunospecific assay. The percentage of C3 fragments to total proteins bound to liposomes increased with the size of liposomes and there was a good correlation between the extent of CF release and the percentage of C3 fragments bound. These results indicated that Man-MLVs released entrapped CF via activating the human complement system and the affinity of Man-MLV to complement increased with the size of Man-MLVs in human plasma. These in vitro results suggest the role of complement as an opsonin in the disposition of Man-MLVs in humans.

Systemic elimination of macrophages using liposomes does not prevent the induction of type I diabetes

Silica treatment of experimental animals leads to a prevention of genetically determined or experimentally induced type I autoimmune diabetes. Since silica is toxic for macrophages an important involvement of these cells in the onset of the disease was concluded. Here we show that in vivo elimination of macrophages by liposome treatment does not lead to prevention of streptozotocin-induced diabetes. The results indicate that the presence of mature macrophages is not an important requisite for diabetes induction and that the effects of silica treatment must be attributed to activation of macrophages leading to disturbed cytokine levels, or to effects on other cell types.

Hypoglycemic effect of intestinally administered monosaccharide-modified insulin derivatives in rats

The effect of the modification of insulin (INS) with p-succinylamidophenyl (SA)-alpha-D-glucopyranoside (SAPG), SA-alpha-D-mannopyranoside and SA-alpha-L-arabinopyranoside on the enzymatic degradation and the hypoglycemic effect in rats was studied. When SAPG-INS was administered intraintestinally in the absence of bile and pancreatic juice, blood glucose level decreased to 56% of initial value. Other monosaccharide derivatives were less effective than SAPG-INS. The digestion of monosaccharide derivatives by pepsin and chymotrypsin indicated that the resistance of insulin to enzymatic degradation was increased by its modification with monosaccharide. One possibility for the hypoglycemic effect of SAPG-INS could be the increased resistance of insulin to enzymatic degradation as a result of its modification with monosaccharide.

Identification of 3-deoxy-manno-2-octulosonic acid, 3-deoxy-5-O-methyl-manno-2-octulosonic acid and 3-deoxy-lyxo-2-heptulosaric acid in the cell wall (theca) of the green alga Tetraselmis striata Butcher (Prasinophyceae)

The main constituent of the cell wall complex carbohydrate of the scaly green alga Tetraselmis striata Butcher is shown to be 3-deoxy-manno-2-octulosonic acid (42%). In addition two other 2-keto-sugar acids are present, namely, 3-deoxy-5-O-methyl-manno-2-octulosonic acid (7%), the first methylated derivative of 3-deoxy-manno-2-octulosonic acid found in nature, and 3-deoxy-lyxo-2-heptulosaric acid (11%). The characterization of the three 2-keto-sugar acids has been carried out on the corresponding methyl ester methyl glycosides using GLC-MS and 500-MHz 1H-NMR spectroscopy, and on the corresponding reduced alditol acetates using GLC-MS. Other monosaccharides occurring in the cell wall are D-galacturonic acid (14%), D-galactose (4%), D-gulose (2%), D-glucose (1%) and L-arabinose (1%).

Affinophoresis of pea lectin and fava bean lectin with an anionic affinophore, bearing rho-aminophenyl-alpha-D-mannoside as an affinity ligand

Affinophoresis is an electrophoretic separation technique for biological polymers with the aid of an affinophore, which is a macromolecular polyelectrolyte bearing affinity ligands. The affinophore migrates rapidly in an electric field, and consequently the electrophoretic mobility of molecules having an affinity for the ligand is specifically changed. An anionic affinophore-bearing mannosyl residue was synthesized for the affinophoresis of lectins. rho-Aminophenyl-alpha-D-mannopyranoside and aminomethanesulphonic acid were coupled to about one-tenth and one-fifth, respectively, of the carboxyl groups of succinyl-poly-L-lysine with an average degree of polymerization of 120 by the use of a water-soluble carbodiimide. Extracts of seeds of pea (Pisum sativum) or fava bean (Vicia fava) were subjected to two-dimensional agarose gel electrophoresis, in which the first dimension was ordinary agarose gel electrophoresis and the second dimension was affinophoresis with the affinophore. The separated proteins were stained with Coomassie Blue R250. The lectins in both seed extracts were separated from a diagonal line formed by other proteins in the extracts. About 10 ng of the separated pea lectin was detected on a nitrocellulose blot by immunostaining with a horseradish peroxidase-conjugated second antibody.

A method for assaying the rhamnosidase activity of naringinase

The use of the p-nitrophenyl-alpha-L-rhamnopyranoside for the specific measurement of the alpha-rhamnosidase activity of naringinase, by colorimetrically following the appearance of p-nitrophenolate anion, is proposed. Use of this synthetic substrate did not change the pH, temperature, or ionic strength optima of the enzyme. It did, however, result in (a) a decrease of the Michaelis constant of the enzyme, allowing the Vmax to be measured, this being impossible to accomplish with naringin, (b) an increase in the sensitivity of the assay to the presence of inhibitors in the reaction media, (c) an increase in the sensitivity which enabled measurement of low levels of naringinase due to the high absorptivity of p-nitrophenolate, and (d) a quick and cheap method of evaluating the alpha-rhamnosidase activity of naringinase.

Simplified concanavalin-A sepharose adsorption method for separation of cone visual pigments from rhodopsin

Batch adsorption of chicken photoreceptor extract using Concanavalin-A Sepharose enables separation of rod and cone pigments and separation of cone pigments of different color sensitivity. In earlier work, column separations using the same adsorption medium, although effective, with high resolution, were slow, demanding and required many differential bleachings of column fractions for analysis. It is shown here that affinity separations can be performed in the batch adsorption mode to purify cattle, frog and chicken rhodopsin. These procedures are more rapid and much more convenient. An extract from the chicken retina can rapidly be separated into four fractions, including three highly enriched (80% or more) visual pigment fractions: (1) extraneous proteins, carotenoids and phospholipids; (2) short wavelength-sensitive pigments; (3) iodopsin; and (4) rhodopsin. While the resolution is not as great as that of the columns, the selectivity is sufficient to produce cone pigments, which are only slightly contaminated with rhodopsin and free of other proteins, either to experiment with directly or to enable heavier loading on high resolution columns. The method is adaptable both to highly labile pigments and to very small quantities, neither of which perform well in column separations.

Steric control in the polymerization of 1,2-anhydro-3,4,6-tri-O-benzyl-beta-D-mannopyranose

Polymerization of 1,2-anhydro-3,4,6-tri-O-benzyl-beta-D-mannopyranose under acid catalysis has led to a series of polymers varying in anomeric configuration from approximately 90% alpha to 70% beta. Optical rotations follow 13C-n.m.r. estimates of anomeric composition linearly over this range. Low-temperature polymerization with trifluoromethanesulfonic anhydride as initiator favors mainly cis-opening of the anhydro ring, presumably through the intermediary of a macroester. These results are compared with related glycosylation and polymerization reactions on 1,2-anhydro sugar derivatives, and some mechanistic conclusions are proposed.

Tumoricidal activation of murine alveolar macrophages by muramyldipeptide substituted mannosylated serum albumin

Rat and mouse alveolar macrophages have almost no spontaneous tumoricidal activity and are only slightly activated by muramyldipeptide (MDP). When MDP was carried by serum albumin, the activation was higher than with free MDP but only at high concentration. When MDP was bound to a neoglycoprotein (mannosylated serum albumin) - which binds to the sugar binding receptor at the macrophage cell surface and is actively endocytosed - the activation of rat or mouse alveolar macrophages is dramatically enhanced even at very low concentration of neoglycoprotein -bound MDP. Furthermore, neoglycoprotein -bound MDP injected i.v. or i.p. was found to be able to activate alveolar macrophages, the activity of which was maximal after 48 hours in mice and 72 hours in rats. Such conjugates have so potential values as new immunostimulant agents in cancer and parasite therapy.

Solution conformation of alpha D(1-3)- and alpha D(1-6)-linked oligomannosides using proton nuclear magnetic resonance

The solution conformations of synthetic methyl mannobiosides and a methyl mannotrioside containing alpha D(1-3) and alpha D(1-6) linkages have been determined through the use of 1H nuclear magnetic resonance techniques, namely, the nuclear Overhauser effect and proton relaxation time measurements. 3J(C,H) coupling constants, obtained from a compound enriched with 13C, were also used. The allowed conformations were found to be in agreement with those determined from potential energy calculations and crystal structures. The methyl mannotrioside is an analogue of a mannotriose unit which occurs naturally in the "core" of asparagine-linked glycopeptides and in an "arm" of high mannose N-linked glycopeptides.

Binding kinetics of methyl alpha-D-mannopyranoside to concanavalin A: temperature-jump relaxation study with 4-methylumbelliferyl alpha-D-mannopyranoside as a fluorescence indicator ligand

The binding of methyl alpha-D-mannopyranoside and methyl alpha-D-glucopyranoside to concanavalin A has been investigated by the temperature-jump relaxation kinetic technique using the competitive inhibitor 4-methylumbelliferyl alpha-D-mannopyranoside as an indicator of the binding reaction. The analysis shows that these saccharides bind to concanavalin A in a single bimolecular step. The binding parameters are compared to those of derivatized carbohydrates which have previously been used to study the binding of saccharides to concanavalin A. The similarity of the association rate constants indicates that a common process is involved in the binding of all carbohydrates to concanavalin A. The different affinities of saccharides for the lectin are primarily due to the different dissociation rate constants. A discussion of the proposed mechanism is given under the Appendix to clarify the fact that one of the observed relaxation times is faster than is possible with only the kinetic indicator reaction.

Loss of lectin-like activity in aberrant type 1 fimbriae of Escherichia coli

Growth of a streptomycin-resistant strain of Escherichia coli (VL-2) in the presence of 30 microgram of streptomycin per ml resulted in the production by these bacteria of structurally altered, nonfunctional type 1 fimbriae. This strain, when grown in this subinhibitory concentration of streptomycin, became incapable of producing mannose-sensitive hemagglutination (<1% of that of the control). Adhering ability to epithelial cells and human leukocytes was also diminished (42 and 7% of that of the control, respectively). Although these streptomycin-treated bacteria were as heavily fimbriated as untreated bacteria, their fimbriae were significantly longer. Furthermore, in contrast to the fimbriae of the untreated bacteria, those isolated from the drug-treated bacteria were found to lack mannose binding activity as measured by hemagglutination. It appears, therefore, that streptomycin can cause even resistant bacteria to produce an aberrant fimbrial protein, possibly by causing misreading of messenger RNA. These studies indicate that the use of sublethal doses of certain antibiotics whose mode of action is well known may shed light on the genetic and chemical modulation of bacterial factors involved in mucosal colonization.

Activation of concanavalin A by Cd2+

Binding of Cd2+ to concanavalin A and the subsequent induction of saccharide-binding activity has been studied at pH 6.5. We found that Cd2+ bound to both metal sites, S1 and S2, and that Cd2+ alone would induce sugar binding in concanavalin A. Using the fluorescent sugar 4-methylumbelliferyl alpha-D-mannopyranoside we determined that full saccharide-binding activity was obtained only when the total bound Cd2+ stoichiometry reached 2 ions/concanavalin A subunit. We also report evidence suggesting that the binding of Cd2+ to S2 is the crucial step in activation and that Cd2+ binding to S1 induces a form of concanavalin A similar to that induced by Zn2+, Ni2+, or Co2+ and different from that induced by Mn2+.

Structure of a mycobacterial polysaccharide-fatty acyl-CoA complex: nuclear magnetic resonance studies

MMP, a linear alpha 1 leads to 4 linked polymer of 3-O-methylmannose, regulates the fatty acid synthetase from Mycobacterium smegmatis by forming stoichiometric complexes with the long-chain acyl-CoA synthetase products. In agreement with previous proposals [Bloch, K. (1977) in Advances in Enzymology and Related Areas of Molecular Biology, ed. Meister, A. (Wiley, New York), Vol. 45, pp. 1-84], nuclear magnetic resonance studies show that the polysaccharide, a random coil in its free form, undergoes a major conformational transition upon enclosing long-chain acyl-CoA. The polysaccharide, probably in helical conformation in the complexed form, interacts with both the paraffinic chain and the CoA moieties of the included fatty acyl thioester.

Binding of manno-oligosaccharides to concanavalin A. Substitution titration with a fluorescent-indicator ligand

The association constants for binding of methyl alpha-D-mannopyranoside (I), mannobiose (II) and mannotriose (III) to concanavalin A were determined in the temperature range 285-313 K by a substitution titration, using 4-methylumbelliferyl alpha-D-mannopyranoside as a carbohydrate-specific and fluorescent indicator. All binding equilibria are simple, but establish extremely slowly with II and III. At 298.3 K, K increases moderately from I to III: (6.4 +/- 0.5) x 10(3), (1.2 +/- 0.1) x 10(4) and (1.10 +/- 0.05) x 10(5) M-1. For binding of I, II and III, the - delta H degree values are constant (36 +/- 2 kJ mol-1) and equal to the average value (36.1 +/- 0.6 kJ mol-1) obtained for the three corresponding 4-methylumbelliferyl alpha-D-manno-oligosaccharides [Van Landschoot, A., Loontiens, F. G., and De Bruyne, C. K (1978) Eur. J. Biochem. 83, 277-285]. The data are interpreted as arising from specific binding to a single mannopyranosyl residue in (alpha 1 leads to 2)-linked manno-oligosaccharides.

I and i antigens of human peripheral blood lymphocytes cocap with receptors for concanavalin A

Surface immunofluorescence experiments using a human anti-i and two anti-I antisera have been performed on human peripheral blood lymphocytes. These are known to contain cold-reactive monoclonal IgM antibodies against the carbohydrate sequence: (formula: see text). A high proportion of B- and T-type lymphocytes express these I and i determinants. In the presence of anti-human immunoglobulin, the cold-reactive membrane-associated complexes of I-anti-I and i-anti-i become stabilized, and redistribution (with patching and capping) can be elicited at 37 degrees C. Dual fluorescence experiments have shown striking concordant staining of I or i (fluorescein) caps and patches with concanavalin A (rhodamine) reactive sites on normal and leukemic cells, suggesting that a proportion of I and i active structures of lymphocyte membranes are structurally associated or physiologically coupled with glycoproteins carrying oligosaccharides with branched mannosyl cores.

Concanavalin A stimulation of plasminogen activator production in pig kidney cells in culture

Addition of subtoxic doses of the lectin concanavalin A to growing subconfluent monolayer cultures of pig kidney cells causes an increase in extra- and intracellular plasminogen activator activity which is reversibly inhibited by actinomycin D, cycloheximide and alpha-methyl-D-mannoside. These results suggest that cell surface events may play an important modulatory role in plasminogen activator production.

Biphasic association of p-nitrophenyl 2-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside and concanavalin A as detected by stopped flow spectroscopy

Kinetics of binding of p-nitrophenyl 2-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside (M2) to concanaviln A (con A) were examined. The time course of formation of a M2 . con A complex is clearly biphasic, whereas the association with con A of p-nitrophenyl 2-O-methyl-alpha-D-mannopyranoside and other monosaccharides is a monophasic process. The biphasic time course of the binding of M2 to conA is most simply explained in terms of a model wherein the disaccharide can bind to con A two different ways. In the initial rapid phase of the biphasic reaction, both complexes form in amounts determined by the relative values of the rate constants for association. In the subsequent slow phase, the complexes equilibriate according to the relative values of the initial constants for formation of each complex. The enthalpy of activation for formation of the initial complexes with M2 is about 4 kcal/mol less favorable than for monosaccharides, whereas the entropy of activations about 14 e.u. more favorable for binding of the disaccharide. These differences in the activation parameters for binding M2 and monosaccharides suggest that con A interacts simultaneously with groups on both mannopyranosyl residues.

Saccharide binding to transition metal ion free concanavalin A

Saccharide binding has been observed with demetallized concanavalin A in the presence of Ca(2+) only, using the fluorescent sugar 4-methylumbelliferyl alpha-D-mannopyranoside. At pH 7.2 both the nicked and intact forms of concanavalin A bound 4-methylumbelliferyl alpha-D-mannopyranoside with similar affinities. Competitive binding with methyl alpha-D-mannopyranoside was demonstrated. The association constants at 5 degrees C were 9.6 +/- 0.6 X 10(4) M(-1) for 4-methylumbelliferyl alpha-D-mannopyranoside and 1.1 +/- 0.3 X 10(4) M(-1) for methyl alpha-D-mannopyranoside. 4-Methylumbelliferyl alpha-D-mannopyranoside binding was also observed if demetallized concanavalin A was remetallized with less than stoichiometric amounts of Ca(2+). The association constants with low Ca(2+) concentrations were similar to those determined with saturating Ca(2+). With less than stoichiometric levels of Ca(2+), the number of sugar molecules bound per protein subunit was a reflection of the fraction of activated lectin subunits. These results show that saccharide binding activity of concanavalin A does not require a transition metal ion at pH 7.2; only Ca(2+) is required. At pH values near 5, where most previous studies have been carried out, both a transition metal ion and Ca(2+) are necessary.

Interaction of calcium and manganese ions with apoconcanavalin A and sugar binding

The interaction of apoconcanavalin A (apo-Con A) with Mn2+ and Ca2+ was studied at 25 degrees C using fluorescence stopped flow. The reaction was monitored using 4-methylumbelliferyl alpha-D-mannopyranoside whose fluorescence is quenched on binding to the metalloproteins. At pH 5.0 entry of Mn2+ into apo is second-order (rate constant = 1.2 x 103 M(-1) s(-1)); at higher pH the rate constant is greater than 104 M(-1) s(-1). Reaction of excess Ca2+ with Mn(Con A) is pseudo-first-order with kobsd = Kk[Ca2+](1 + K[Ca2+])(-1). This is interpreted as rapid formation of unlocked MnCa(Con A), with a formation constant K = 3.5 x 102 M(-1), which transforms (k = 0.026 s(-1)) to a locked form, indistinguishable from native. At pH 6.4 and 7.2, K greater than or equal to 103 M(-1) and k = 0.043 and 0.050 s(-1), respectively. Ca(Con A) and Mn(Con A) precipitate glycogen and bind to 4-methylumbelliferyl alpha-D-mannopyranoside as effectively as native protein at pH 7.2. Treatment of the Ca or Mn forms with EDTA produces an apo form with a small binding capacity, which it loses slowly.

Glycosidases of the retinal pigment epithelium

The pH optima and apparent Km and Vmax values were determined for nine glycosidases of the retinal pigment epithelium (RPE) of the calf. In terms of micromoles of substrate cleaved per milligram protein per hour, the following relative order of enzymatic activities was observed: beta-N-acetylglucosaminidase greater than alpha-glucosidase = beta-N-acetylgalactosaminidase greater than alpha-mannosidase greater than beta-galactosidase greater than beta-glucosidase greater than alpha-fucosidase greater than alpha-galactosidase greater than beta-glucuronidase. The pH optimum of each of these enzymes was in the acidic range (below pH 6). All these findings refer to enzymatic activities of bovine RPE preparations obtained by the brushing procedure of Glocklin and Potts and washing as described by Berman and Feeney. Thus they may relate to those activities associated with particulate components of the RPE cell and not to the more soluble glycosidases. The distribution of the glycosidases between the washes of the cells and the final pellet of bovine RPE cells was examined. The activities of 10 glycosidases in the RPE of the embryonic chick were also examined. Neither beta-mannosidase nor beta-fucosidase activities could be detected in washed bovine RPE cells, although beta-mannosidase was detected in RPE of the embryonic chick. The presence of isoenzymes of beta-glucuronidase in bovine RPE was indicated. Specificity by beta-glucuronidase of bovine RPE for synthetic substrates was observed.

Sugar binding properties of various metal ion induced conformations in concanavalin A

Concanavalin A is known to undergo a first-order conformational transition when metals are added to the demetallized protein at pH 5.6 (Brown, R.D., III, et al. (1977) Biochemistry 16, 3883--3896). The rate constants for this process, which wer have measured using a polarographic technique, are identical when zinc, cobalt, or manganese occupies S1 and calcium occupies S2. The reducible sugar, p-nitrophenyl alpha-D-mannopyranoside, binds only to the locked conformational structure which is formed upon the addition of metals. The affinity of the protein for sugars is dependent upon occupancy of S1 and S2 and quite sensitive to the identity of the metal in S2. The metals may be removed from the locked protein structure and the protein temporarily retains its ability to bind with sugars but with a considerably lower affinity. The locked form of concanavalin A is unstable at a pH near 2 and unfolds to the unlocked structure with a half-life of 25 min resulting in simultaneous loss of metal and sugar binding.

Interactions between chondroitin sulfate and concanavalin A

Chondroitin sulfate, the major extracellular matrix glycosaminoglycan, formed an insoluble complex with concanavalin A at pH 5.4 or below. Concanavalin A (500 microgram/ml) reacted only within a relatively narrow concentration range of chondroitin sulfate (optimally between 5 and 50 microgram/ml) at pH 5.4 in 0.05 M buffer. Similar precipitin-like interactions were seen between concanavalin A and hyaluronic acid or heparin. No precipitating complexes formed between concanavalin A and the glycosaminoglycans at these concentrations in physiological salt solutions (approx. 0.15 M) unless the pH was below 4.5. Precipitating self-aggregates of concanavalin A appeared to be promoted by chondroitin sulfate at pH 7.3, but no significant precipitation occurred between the reactants at this pH even at very high concentrations, nor did soluble complexes form as determined by affinity chromatography on Sephadex G-200 or fractionation on Bio-Gel P-200. Thus, binding between the lectin and glycosaminoglycans appeared to depend upon reversible non-specific electrostatic interactions observed only at low Ph and low ionic strength. Stable interactions were not seen in experiments using physiologically balanced salts at near neutral pH.

Binding of 4-methylumbelliferyl alpha-D-mannopyranoside to tetrameric concanavalin A Fluorescence temperature-jump relaxation study

The kinetics of saccharide binding to the treatment form of concanavalin A have been studies at pH 7.2 with the temperature-jump method. 4-Methylumbelliferyl alpha-D-mannopyranoside was used as a ligand; its fluorescence is totally quenched upon binding. A single relaxation of ligand fluorescence (tau = 20-400 ms) was observed and was investigated at three different temperatures, using kinetic titration and dilution types of experiments. The concentration dependence of the relaxation time and amplitude was consistent with a single-step bimolecular association and independent binding sites. In the temperature range 13-24 degrees C the association and dissociation rate parameters are in the range (6-10) X 10(4) M-1 s-1 and (1.4-3.2)s-1 respectively, corresponding to activation energies for the forward and reverse reactions equal to approx. 13 and 8 kcal/mol (54 and 33 kJ/mol) respectively. Two additional relaxations of protein fluorescence (3 ms and larger than 1 s at 25 degrees C) were unaffected by carbohydrate binding. Tetrameric concanavalin A shows carbohydrate binding parameters that are almost identical to those of native or derivatized dimeric concanavalin A.

Multiple alpha-mannosidase activities in mammalian tissues as shown by metal-ion activation

1. Four different types of alpha-mannosidase activity were shown to occur in several tissues from the rat. There is the Zn2+-dependent enzyme, active at acidic pH, and three enzymes that are active near to neutral pH. 2. The 'neutral' enzymes are activated by Fe2+, Co2+ or Mn2+. 3. Optimum activities for these three enzymes are shown at pH values of 5.2, 6.5 and 7.3. The activity at pH6.5 is the only one evident without metal-ion activation, but activity is enhanced by all three metal ions. The activity at pH 5.2 is seen only in the presence of Fe2+ or Co2+, and the activity at pH7.3 is seen only in the presence of Co2+ or Mn2+ and in a non-chelating buffer medium. 4. The pH6.5-active enzyme is inactivated by EDTA, but activity is restored by excess of metal ion. 5. The enzymes differ markedly in their stability. The pH6.5-active enzyme is very labile and the pH7.3-active enzyme is the most stable. 6. Tissue preparations vary widely in their activity at pH6.5, but where activity is low it can be increased by incubation with one of the activating metal cations. 7. All the enzymes active at neutral pH are inhibited by heavy-metal ions and stabilized to some extent by thiol groups.

Purification and properties of a beta-mannosidase from Aspergillus niger

A beta-mannosidase (beta-D-mannoside mannohydrolase, EC 3.2.1.25) was purified to apparent homogeneity from the culture filtrate of the fungus, Aspergillus niger. The enzyme had an estimated molecular weight of about 120,000 and was a glycoprotein. Radioactive enzyme was prepared by growing the fungus in [14C]fructose, and this enzyme was used for the preparation of 14C-glycopeptides. The glycopeptides were purified on Sephadex G-25 and G-50 and were then hydrolyzed for sugar analysis. Two radioactive sugars were found in the glycopeptides and these were identified as mannose and glucosamine in a ratio of 2.5 or 3:1. Based on susceptibility of the enzyme to alkaline treatment and the formation of [3H]glucosaminitol in the presence of NaB3H4, the oligosaccharide is apparently attached to the protein in a GlcNAc-asparagine linkage. The beta-mannosidase had good activity on p-nitrophenyl-beta-D-mannoside but was inactive on p-nitrophenyl-alpha-D-mannoside as well as on other p-nitrophenyl glycosides. It also showed good activity on the beta(1 leads to 4)-linked trisaccharide of mannose and somewhat lower activity of the corresponding disaccharide. With each of these substrates the Km was about 1 mM, whereas with the p-nitrophenyl-beta-D-mannoside the Km was about 2 mM. The beta-mannosidase also released [14C]mannose from the Man-GlcNAc-GlcNAc trisaccharide isolated from the lipid-linked oligosaccharides of aorta and released mannose from the disaccharides, Man-(beta1 leads to 4)GlcNAc and Man-(beta1 leads to 4)ManNAc. The pH optimum for the enzyme was about 3.5 to 4.0 in glycine or acetate buffer.

Determination of the anomeric configurations of Corbicula ceramide di- and trihexoside by chromium trioxide oxidation

The anomeric configurations of Corbicula ceramide dihexoside and ceramide trihexoside were determined by chromium trioxide oxidation and the structures of these lipids were shown to be Man-beta(1 leads to 4)-Glc-beta(1 leads to 1)-ceramide and Man-alpha(1 leads to 4)-Man-beta(1 leads to 4)-Glc-beta(1 leads to 1)-ceramide. These results are compatible with those obtained by enzymic hydrolysis reported previously.

Purification and interaction with estradiol-17beta

The combination of polyacrylamide gel electrophoresis and Concanavalin-A-Sepharose affinity chromatography has permitted the isolation on a preparative scale, of four molecular forms of rat alpha1-fetoprotein: a "slow" and a "fast" fraction, each separable into Concanavalin-A-adorbed ("high carbohydrate", i.e. rich in accessible alphaD-Mannosyl and alphaD-Glucosyl residues) and a Concanavalin-A-non adsorbed ("low carbohydrate") fractions. These four iso-alpha-fetoproteins (iso-AFP) bind estradiol-17beta. However, they disclose differences in both their association constants and number of binding sites for this hormone. Very high affinity sites (10(9)) are mainly located on the "slow-low carbohydrate" form. Low affinity, high capacity sites are preferentially located on the "high carbohydrate" form. These results confirm the molecular and functional heterogeneity of rat AFP and suggest that the carbohydrate moiety of the protein may have a role in estrogen-AFP interactions.

Colony stimulating factor (CSF) from human leukemic urine: affinity chromatography and isoelectric focusing

Biological activities associated with colony-stimulating factor (CSF) from human leukemic urine were found to be selectively retained on an affinity adsorbent of Con A-Sepharose. Elution of activity was achieved using a linear gradient of eith alpha-methyl-D-mannopyranoside (alphaMM) or alpha-methyl-D-glucopyranoside (alphaMG), and resulted in significant increases in specific biological activity. Rechromatography of appropriate fractions indicated that retention of CSF activities was not artifactual. Pretreatment of the affinity matrix with alphaMM completely inhibited binding of CSF. Affinity chromatography of CSF on a Blue Dextran-Sepharose adsorbent was found to be an effective method for removing albumin, a major protein contaminant in urinary preparations. Treatment of CSF with neuraminidase had no effect on its in vitro activity; however, such treatment resulted in an increase in the isoelectric point of CSF from pH 3.5 to pH 4.7, as determined using both sucrose and polyacrylamide gel stabilized pH gradients. Relatively broad regions of biological activity were observed following isoelectric focusing of both neuraminidase-treated and untreated CSF, suggesting that activity was associated with a heterogeneous/polydisperse population of molecular species.

Photoaffinity labeling of concanavalin A. Preparation of a concanavalin A derivative with reduced valence

Concanavalin A (Con A) was labeled with p-azidophenyl alpha-D-mannopyranoside under ultraviolet irradiation and the reaction products were separated by affinity chromatography on Sephadex G-100 at pH 5. One of the Con A derivatives thus obtained was characterized as a monovalent dimer at pH 5 and a divalent tetramer at pH 7 by sedimentation equilibrium and equilibrium dialysis, indicating that this photoaffinity labeling did not alter the quaternary structure of Con A. In agreement with these results, the labeled Con A did not show the capacity to precipitate glycogen at pH 5, but it formed precipitates with glycogen at pH 7. Although its hemagglutinating activity was found to be weaker than that of the native Con A, the dose-response cure of the labeled Con A in the mitogenic stimulation of human peripheral lymphocytes was almost identical to that of the native con A.