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.