Protein-ligand interaction. A calorimetric study of the interaction of oligosaccharides and hen ovalbumin glycopeptides with concanavalin A

The forgotten sugar: A review on multifarious applications of melezitose

Although, 187 years elapsed after the discovery of melezitose, it is a high time to deduce some solid applications as there are only 13 more years left to celebrate a double century of this sugar. The forgotten sugar has multifarious applications; it is used as a metabolic marker to differentiate melezitose fermenting microorganisms, as a carbon source to culture specific microorganisms, as a potential surfactant and excipient to stabilize pharmaceuticals, as a lyoprotectant or cryoprotectant for several industrial applications, as an edibility enhancer in food industry, as a hair smoothening agent in cosmetic industry, and provide protective & nourishing effects in fisheries and aquaculture industries. In entomological research, it is used to study niche differentiation, increased longevity of insects and also as a biocontrol agent. This review brings out the best possible applications of melezitose and present in the form of a mnemonic to remember this forgotten sugar.

Microbead analysis of cell binding to immobilized lectin. Part II: Quantitative kinetic profile assay for possible identification of anti-infectivity and anti-cancer reagents

There has been a re-emergence of the use of lectins in a variety of therapeutic venues. In addition lectins are often responsible for the binding of pathogens to cells and for cancer cell clumping that increases their escape from body defenses. It is important to define precisely the activity of inhibitors of lectin-binding that may be used in anti-infection and anti-cancer therapeutics. Here we describe a kinetic assay that measures the activity of saccharide inhibitors of lectin binding using a model system of yeast (Saccharomyces cerevisiae) and lectin (Concanavalin A, Con A) derivatized agarose microbeads that mimics pathogen-cell binding. We show that old methods (part I of this study) used to identify inhibitor activity using only one sugar concentration at one time point can easily provide wrong information about inhibitor activity. We assess the activity of 4 concentrations of 10 saccharides at 4 different times in 400 trials and statistically evaluate the results. We show that d-melezitose is the best inhibitor of yeast binding to the lectin microbeads. These results, along with physical chemistry studies, provide a solid foundation for the development of drugs that may be useful in anti-infectivity and anti-cancer therapeutics.

Electrochemical sensing of concanavalin A using a non-ionic surfactant with a maltose moiety

To electrochemically detect concanavalin A (ConA), a new method was developed using mixed micelles between a non-ionic surfactant with a maltose moiety and electroactive daunomycin. The surfactants, in which the length of the alkyl chain was different, were n-decyl-β-D-maltoside, n-dodecyl-β-D-maltoside, and n-tetradecyl-β-D-maltoside. The measurement principle was due to the micelle breakdown caused by the binding between the ConA and maltose moieties. When ConA was combined with maltose moieties at a concentration of surfactant that was near the critical micelle concentration, the daunomycin that formed the micelles was moved to a solution from the micelles. As a result, the peak current of daunomycin increased as the concentration of ConA was increased. The mechanism was proposed using voltammetry, spectrometry, and gel filtration. The linear range using n-tetradecyl-β-D-maltoside was 2.0×10(-9) to 8.0×10(-8) M of ConA, and it was the most sensitive in the presence of the three surfactants. To examine whether selective binding took place, measurements with several proteins were carried out. The electrode responses of daunomycin were not influenced by the presence of 5.0×10(-6) M protein. Furthermore, this method could be applied to the determination of ConA in a serum, and to the measurement of sugar chains that can be combined with ConA on the cell surface.

Microbead analysis of cell binding to immobilized lectin: an alternative to microarrays in the development of carbohydrate drugs and diagnostic tests

Microarray technology is currently used in the development of carbohydrate drugs and diagnostic tests. Here we model an inexpensive alternative to microarrays using derivatized microbeads. In this model we examine the binding of mannose-rich yeast to microbeads derivatized with concanavalin A (Con A), a mannose-binding lectin, in the presence of 30 different sugars and 9 different pH conditions. We developed a listing of effective saccharide inhibitors of immobilized Con A based on 3901 replicates. We suggest that this is the most extensive saccharide inhibitor list ever developed for this lectin and it may be useful to use this listing to replace the less extensive lists that have been in the literature for decades. Information is also provided on pH effects on immobilized Con A binding based on 918 trials. Two assays to study binding, one which qualitatively scores more or less binding than control in thousands of replicate samples, and another that quantitatively evaluates binding by counting the number of cells bound to each bead, are also modeled here. We know of no previous studies that provide such extensive information on saccharide inhibition and pH effects on the binding of immobilized Con A. We suggest that this microbead approach, using beads derivatized with lectins or sugars, and the two simple assays presented here, can in some cases substitute for more expensive microarray technology in the development of carbohydrate drugs and diagnostic tests. If, for example, our model Saccharomyces cerevisiae was a pathogen, these studies show that it binds via cell surface mannose residues and drugs to prevent binding could be developed using the inhibitors of binding identified here. The beads could be also used in the development of diagnostic tests that identify the presence of the organism in blood samples, etc. in much the same way as microarray technology is being used today.

Multisite and multivalent binding between cyanovirin-N and branched oligomannosides: calorimetric and NMR characterization

Binding of the protein cyanovirin-N to oligomannose-8 and oligomannose-9 of gp120 is crucially involved in its potent virucidal activity against the human immunodeficiency virus (HIV). The interaction between cyanovirin-N and these oligosaccharides has not been thoroughly characterized due to aggregation of the oligosaccharide-protein complexes. Here, cyanovirin-N's interaction with a nonamannoside, a structural analog of oligomannose-9, has been studied by nuclear magnetic resonance and isothermal titration calorimetry. The nonamannoside interacts with cyanovirin-N in a multivalent fashion, resulting in tight complexes with an average 1:1 stoichiometry. Like the nonamannoside, an alpha1-->2-linked trimannoside substructure interacts with cyanovirin-N at two distinct protein subsites. The chitobiose and internal core trimannoside substructures of oligomannose-9 are not recognized by cyanovirin-N, and binding of the core hexamannoside occurs at only one of the sites on the protein. This is the first detailed analysis of a biologically relevant interaction between cyanovirin-N and high-mannose oligosaccharides of HIV-1 gp120.

Fluorescence Anisotropy Assays Reveal Affinities of C- and O-Glycosides for Concanavalin A(1)

The free energies of binding of various C- and O-glycosides to the lectin concanavalin A were measured using fluorescence anisotropy. Fluorescein derivatives of mannose and glucose were synthesized and were shown to bind to concanavalin A with free energies of -5.1 and -4.3 kcal mol(-)(1), respectively. Competition experiments were performed to determine the binding energies of different nonfluorescent carbohydrates, and the results were in excellent agreement with the binding energies determined by microcalorimetry. The minimum carbohydrate epitope that fills the lectin carbohydrate binding site, methyl 3,6-di-O-(alpha-mannopyranosyl)-alpha-mannopyranoside, competes directly for the site with the fluorescent ligands, indicating that the fluorescent ligands bind specifically. The binding affinities of C-glycosides to concanavalin A were compared with those of O-glycosides. The free energies of binding for corresponding C- and O-glycosides differed by less than 0.5 kcal mol(-)(1), indicating that recognition properties of C- and O-glycosides are very similar. It was found that for some ligands the use of a carbon linkage rather than an oxygen linkage caused the specificity of binding to decrease slightly.

Sensitive titration microcalorimetric study of the binding of Salmonella O-antigenic oligosaccharides by a monoclonal antibody

The binding of several oligosaccharide haptens by a monoclonal antibody, Se155-4, specific for Salmonella serogroup B O-antigen was studied by titration microcalorimetry. In the software developed by Wiseman et al. [Wiseman, T., Williston, S. & Brandts, J.F. (1989) Anal. Biochem. 17, 131-137] the number of binding sites/macromolecule is one of the optional regression parameters in the non-linear least-squares analysis of the calorimetric data. Instead, an approach was adopted in which the concentration of binding sites was treated as a regression parameter, obviating the requirement for precise values of antibody absorption coefficients and minimizing effects due to partially inactive antibody preparations. Furthermore, performing the least-squares analysis in two steps, first using a differential heat mode and then an integral heat mode, was shown to yield the most accurate results. The technique gave accurate results using not more than 1-2 mumol ligand and less than 7 mg antibody. Haptens 2-5 were oligomers of the O-antigenic repeating unit varying in chain length by 2-5 repeating units and a trisaccharide glycoside 1, which filled the binding site. The latter hapten exhibited a favourable entropy contribution to binding (delta Go = -31 kJ.mol-1; delta Ho = -21 kJ.mol-1 and -T delta So -10 kJ.mol-1), while all four oligomers 2-5 showed a constant binding energy delta Go = -33 kJ.mol-1, composed of increasingly stronger enthalpy forces compensated by an increasingly unfavourable entropy contribution. These observations are compared with results from enzyme immunoassays and a high-resolution crystal structure for the dodecasaccharide 3 bound to the Fab derived from Se155-4.

Binding of lanthanum and gadolinium ions to concanavalin A studied calorimetrically at 25 degrees C

The interaction between Concanavalin A (ConA) and the lanthanide ions La3+ and Gd3+ has been studied calorimetrically at 25 degrees C. The measurements were carried out at a pH of 4.5, where the protein exists prevailingly as a dimer. Calorimetry allows the direct determination of the binding enthalpy and the evaluation of both the apparent association constant, and the apparent free energy and entropy. Three groups of data were collected. The first concerns the interaction of the 'native' protein, i.e., fully metallized with Mn2+ and Ca2+, with the lanthanides. The second concerns the interaction of the completely demetallized protein with La3+ and Gd3+. Finally, the affinity of each complex was tested for the specific sugar alpha-methylmannopyranoside. The analysis of the thermodynamic parameters obtained, led to the following conclusions: 1) a specific site, named S3, exists on the protein for the lanthanides, distinct from the S1 site of the transition metal and from the S2 site, specific for calcium. There is only one S3 site per protomer when the protein has Mn2+ in S1 and Ca2+ in S2. Moreover, there is no appreciable competition for S1 and S2 from the lanthanides. The 'native' protein, metallized with La3+ or Gd3+, is a fully functional protein. 2) The demetallized protein (ApoCon A) has at least two sites per protomer for the lanthanides. The hypothesis is that, besides the S3 site, the lanthanides, in the absence of Mn2+, can also occupy the S1, but not the S2, site. The protein metallized only with gadolinium ion is completely inactive toward the interaction with the mannoside. The same happens when, along with gadolinium, only calcium or manganese is present. Hence, in the absence of the transition metal in S1 or of calcium in S2, the protein is not in the conformation suitable to interact with its specific substrate.