A rapid and sensitive assay for detection of nanogram quantities of castor-bean (Ricinus communis) lectins

Sugar-quantum dot conjugates for a selective and sensitive detection of lectins

One-pot synthesized neoglycoconjugates with a reactive thiol group are introduced here for functionalization with carbohydrates for solubilization and stabilization of CdSe-ZnS quantum dots in aqueous solution. Three different sizes of quantum dots (QDs) with lactose, melibiose, and maltotriose on their surface have been utilized, for the first time, for lectin detection through agglutination assay. The sugar-QDs thus synthesized were characterized by transmission election microscopy (TEM), fluorescence, and absorption spectroscopy. Agglutination of sugar-QDs by three different lectins occurred through specific multivalent carbohydrate-lectin interactions and was studied extensively by monitoring the scattered light at 600 nm. This assay was very selective, which has been demonstrated by a more selective binding of soybean agglutinin (SBA) with melibiose-QD, as compared to lactose-QD, and specific deagglutination caused by alpha-d-galactose, while alpha-d-mannose did not show any effect. The detection sensitivity of the maltotriose-QD was tested with Concanavalin A (ConA), and as little as 100 nM of the lectin was detected using light scattering. The detection sensitivity of this protocol has been enhanced considerably by the fluorescence properties of QDs. This agglutination process seems to occur through formation of smaller soluble aggregates, which further associate to form larger aggregates.

Detection of ricin and other ribosome-inactivating proteins by an immuno-polymerase chain reaction assay

Ribosome-inactivating proteins (RIPs) are plant proteins with enzymatic activity, classified as type 1 (single chain) or type 2 (two chains). They are identified as rRNA N-glycosidases (EC 3.2.2.22) and cause an irreversible inhibition of protein synthesis. Among type 2 RIPs, there are potent toxins (ricin is the best known) that are considered as potential biological weapons. The development of a fast and sensitive method for the detection of biological agents is an important tool to prevent or deal with the consequences of intoxication. In this article, we describe a very sensitive immuno-polymerase chain reaction (IPCR) assay for the detection of RIPs-a type 1 RIP (dianthin) and a type 2 RIP (ricin)-that combines the specificity of immunological analysis with the exponential amplification of PCR. The limit of detection (LOD) of the technique was compared with the LODs of the conventional immunological methods enzyme-linked immunosorbent assay (ELISA) and fluorescent immunosorbent assay (FIA). The LOD of IPCR was more than 1 million times lower than that of ELISA, allowing the detection of 10 fg/ml of dianthin and ricin. The possibility to detect ricin in human serum was also investigated, and a similar sensitivity was observed (10 fg/ml). IPCR appears to be the most sensitive method for the detection of ricin and other RIPs.

Glycation increases the permeability of proteins across the blood-nerve and blood-brain barriers

Our previous investigations have demonstrated increased permeability across the blood-nerve barrier of human plasma albumin after glycation with D-glucose [J.F. Poduslo and G.L. Curran, Proc. Natl. Acad. Sci. USA, 89 (1992) 2218-2222]. In the present investigation, the generality of this observation was evaluated by measuring the permeability coefficient-surface area product (PS) after correction for the residual plasma volume (Vp) across the blood-nerve barrier (BNB), as well as the blood-brain barrier (BBB), for nerve growth factor (NGF) and human IgG after in vitro glycation with D-glucose using an i.v. bolus injection technique in the cannulated brachial vein and artery of normal adult rats. Glycated proteins (gNGF and gIgG) had significantly decreased circulating plasma half-lives compared to the non-glycated proteins. The PS across the BNB obtained for gNGF was significantly increased compared to NGF with a 2.0-fold increase observed after 8 weeks of glycation and a 5.1-fold increase at 21 weeks of glycation. The Vp measurement for NGF and gNGF across the BNB was not significantly different at 8 weeks of glycation but was 1.3-fold greater at 21 weeks of glycation. The PS across the BBB for gNGF was about 2-fold greater than NGF with a glycation time of 8 weeks and 3.2-3.6-fold greater with a glycation time of 21 weeks for six different brain regions. No changes were observed in the Vp for any of the brain regions for gNGF compared to NGF. The PS across the BNB for gIgG compared to IgG was significantly greater with a 4.1-fold relative increase and no significant difference in the Vp values.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein blotting: detection of proteins with colloidal gold, and of glycoproteins and lectins with biotin-conjugated and enzyme probes

Methods to detect "native" proteins immobilized on nitrocellulose membranes in spot tests or on blots prepared from polyacrylamide slab gels after electrophoretic separation are described. Gold sols were found to be useful as general stains for proteins: They are polychromatic, yield an indelible record, and are complementary to india ink as protein stains because these two stains have different sensitivities for a number of proteins tested. For detection of wheat germ lectin (WGL)-binding glycoproteins, avidin-peroxidase was an effective enzyme probe, because the glycoportion of the avidin moiety possesses binding affinity to WGL. Glycocomponents in human parotid saliva were detected with this probe and with the following biotin-conjugated lectins as intermediary probes: soybean lectin, Bandeiraea simplicifolia lectin, Lotus tetragonolobus lectin, and kidney bean lectin. Autoclaving blots prior to probing eliminated endogenous peroxidase activity. Concanavalin A and WGL were separated by isoelectric focusing and detected on blots with horseradish peroxidase and avidin-peroxidase, respectively. The versatility of the biotin/avidin system was used to detect other lectins on similar blots using biotin-conjugated glycoproteins as intermediary probes: Helix pomatia lectin and B. simplicifolia lectin were detected with biotinyl neoglycoproteins, and kidney bean lectin with biotin-conjugated components of parotid saliva.

A simple and rapid method for quantification of hapten specific antibodies

A sensitive and simple method for quantitation of antibodies against small molecules is described using DNP-lysozyme as the enzyme conjugate. The anti-DNP antiserum was raised against DNP-bovine serum albumin conjugate. Anti-DNP antibody or its monovalent fragment (Fab) reduced the enzyme activity of DNP-lysozyme conjugate in a concentration-dependent manner. The inhibition of enzyme activity is a specific measure of the antibody and Fab content of the sample. The specificity of the reaction was assessed by reduction of antibody-induced inhibition by DNP-lysine. The ability of DNP-lysine to reduce the antibody-induced inhibition of DNP-lysozyme activity also makes possible a sensitive assay for DNP-lysine.

Preparation, properties, and applications of carbohydrate conjugates of proteins and lipids

As a result of the growing awareness of the involvement of the oligosaccharide moieties of glycoproteins and glycolipids in cell surface recognition and binding phenomena, a wide variety of methods have been developed, many quite recently, for preparing glycoconjugates. The chemical methods used for the attachment of sugars and certain hydrophilic polymers (e.g., polyethylene glycol) are discussed, as are the effects of such modifications on various properties of the protein (immune response, thermal stability and resistance to proteolysis, clearance, and specific binding to cell surface receptors). Enzymatic approaches to glycoconjugate preparation are also considered, and several examples are given of the preparation of model glycolipids, useful in studying cell surface phenomena. In a final section, three areas are considered in which rapid advances seem likely to occur: improved methods for the preparation of glycoconjugates; direct modification of cell surface glycoconjugates; and modification for the purpose of studying location and environment of membrane glycoconjugates.