Concanavalin with dextrans

Silica gel coated with dextran or agarose Protein A, concanavaline A [139]... 

Kokufuta, Zhang and Tanaka developed a gel system that undergoes reversible swelling and collapsing changes in response to saccharides, sodium salt of dextran sulfate (DSS) and a-methyl-D-mannopyranoside (MP) [126]. The gel consists of a covalently cross-linked polymer network of W-isopropylacrylamide into which concanavalin A (ConA) is immobilized. As shown in Fig. 31, at a certain temperature the gel swells five times when DSS ions bind to ConA due to the excess ionic pressure created by DSS. The replacement of the DSS by non-ionic MP brings about collapse of the gel. The transition can be repeated with excellent reproducibility. 

Fig. 7A—C. Biochemo-mechanical function of NIPA gel with immobilized concanavalin A (A) Schematic illustration of saccharide-responsive, reversible swelling of a NIPA gel loaded with concanavalin A. Na DS"- is dextran sulfate sodium (DSS). (B) Temperature dependence for equilibrated volume of NIPA gel including the Con A-DSS complex (DSS-gel, O), MP (MP-gel, ), and free of both DSS and MP (A). The latter was prepared as a control sample as described in the text except for the use of an aqueous Con A solution instead of the Con A-DSS solution. Hysteresis was observed in the volume changes of the MP-gel and free-Con A gel on heating and cooling, indicating a discontinuous phase transition. The diameter of each gel in the collapsed state, determined at 50 °C, was d0 = 0.074 mm the volume of this gel is denoted Vp. The concentration of dry matter in the collapsed state was estimated from the preparation recipe to be 90 wt%. (C) Repeated swelling/shrinking control at 34.5 °C by alternate binding of DSS and MP to gel-entrapped Con A. (E. Kokufuta, Y.-Q. Zhang and T. Tanaka [78])...

Several processes in the immune response are affected by lithium in vivo and in vitro 139). The proliferative responses of hamster lymphoid cells to concanavalin A or phytohemagglutinin, which stimulate mitosis in T cells, were enhanced by lithium in a serum-free culture system. Proliferative stimulation also was obtained with lithium using the B cell mitogen lipopolysaccharide, but the B cell mitogens dextran sulfate and trypsin had no effect 140-143). Lithium increased the effects of suboptimal concentrations of stimulants, but had smaller effects on stimulation by optimal concentrations. With concanavalin A, the response to optimal stimulatory concentrations was inhibited 140). Paradoxical results such as these may be due to inhibitory effects of lithium on adenylate cyclase, or to effects on membrane transport systems 141). Most of these experiments used very high concentrations of lithium, considerably in excess of normal therapeutic doses (maximal inhibitory concentrations were 10 mM with hamster cells and 5 mM with human lymphocytes). At therapeutic levels of lithium, increased incorporation of [ H]thymidine was seen in human peripheral blood mononuclear cells. 

Without doubt, concanavalin A (Con A) is the most celebrated and has proven to be one of the most useful of the plant lectins. Its physical chemical properties and carbohydratebinding properties are well documented in previous reviews [3,8]. Suffice it to note that it was first isolated and crystallized by Sumner and Howell in 1936, who showed it to require metal ions for its activity [74]. By virtue of its interaction with branched a-D-glucans, it is readily prepared by affinity chromatography on crossed-linked dextran (Sephadex) [75, 76]. A homotetramer at pH 7 (subunit M, = 26 500 Da) of Con A has been sequenced [77] and its crystal structure determined both in its native form [38,39] and complexed with methyl a-D-mannopyranoside [40] and Man(al-3)[Man(al-6)]Man[49]. 

Figure 1 Uptake of PLGA nanoparticles containing tetramethylrhodamine-labeled dextran by monocyte-derived human immature DCs in culture. DC surface was labeled FITC-labeled concanavalin and shows veiling on the cell membrance (A). Pretreatment of cells with cytochalasin B resulted in inhibition of the nanoparticle uptake (C) whereas placebo treated cells showed strong uptake (B). ) (From Ref 125.)...

The spot test described herein is based on the Viscometric Affinity Assay (VAA) described earlier [/, 2]. The principle of the VAA is based on the fact that the mixture of the glucose-specific lectin Concanavalin A (ConA, [3,4]) with a highly concentrated dispersion of 1,000 kDa dextran (wt 1-10%) yields a tremendous rise of the resulting viscosity (up to 20 times). Such viscous dispersions can adopt gel-like properties as discussed in detail by Ehwald et al. [5]. This viscous behavior is due to extensive intermolecular affinity crosslinking of dextran molecules by ConA (see Figure la). 

Figure 8.16. Bioaffinity sensor with concanavaline A and dextran marked by fluorescing group...

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