Studies on chemical modification of cold agglutinin from the snail Achatina fulica

Cold Agglutinin Disease in a Rhesus Macaque (Macaca mulatta)

Cold agglutinin disease (CAD) is a condition involving anemia and its related symptoms; it is caused by autoantibodies that bind and agglutinate red blood cells in areas susceptible to hypothermia, such as extremities exposed to cold temperatures. CAD is rare, with 5 to 20 human cases per million individuals. In this report, we describe a case of CAD in a previously healthy and experimentally naïve adult Indian rhesus macaque that was housed indoors and presented with blood in the urine. After our observations of hemoglobinuria and anemia led us to suspect CAD, we demonstrated that the macaque's blood agglutinated at reduced temperatures. We also noticed that the provision of cold foraging treats triggered episodes of hemoglobinuria. Further investigation revealed that serum from the macaque agglutinated RBCs in vitro with high thermal amplitude (at or below 30 °C) and had an antibody titer of 8 to 32. The serum contained autoantibodies of the immunoglobulin M (IgM) isotype; agglutinins of the IgG isotype were not detected. The cold-dependent IgM autoantibodies in the serum from the affected macaque reacted against a common RBC antigen because RBCs collected from other macaques were bound and agglutinated by the affected animal's IgM under cold conditions. This in vitro binding activity was reversible when the test temperature was returned to normal body temperature (37 °C). These findings demonstrated cold-dependent RBC-specific IgM agglutinins and led us to a diagnosis of CAD. This is the first documented case of spontaneous CAD in a rhesus macaque.

Chemical modification studies of Artocarpus lakoocha lectin artocarpin

The effect of chemical modification on an anti T-like lectin, artocarpin isolated from Artocarpus lakoocha seeds was investigated in order to identify the type of amino acids involved in its agglutinating activity. Modification of carboxyl groups, arginine and lysine residues, did not affect the lectin activity. However, modification of tryptophan, tyrosine and histidine residues led to a complete loss of its activity, indicating the involvement of these amino acids in the saccharide-binding ability. A protection was observed in the presence of inhibitory sugar. A marked decrease in the fluorescence emission was found when the tryptophan residues of lectin were modified. The circular dichroism spectra showed the presence of an identical pattern of conformation in the native and modified lectin, indicating that the loss in activity was due to modification only. The effect of pronase on artocarpin showed loss of activity whereas papain and trypsin had no effect. The specific activity of artocarpin remained unaltered on treatment with glycosidases but remarkable increase in the activity (of the same) was observed with xylanase treatment. Immunodiffusion studies with chemically modified lectin showed no gross structural changes, indicating that the group specific modifying agents did not alter the antigenic sites of the modified lectin.

Chemical modification studies on a blood group A-specific lectin, crotalarin (Crotalaria striata) and its effect on hemagglutinating activity

Crotalarin, the N-acetyl-D-galactosamine-binding blood group A-specific lectin from the seeds of Crotalaria striata was subjected to various chemical modifications in order to ascertain the amino acid residues responsible for its carbohydrate-binding property. Modification of lysine, cysteine and arginine residues did not affect the carbohydrate-binding activity of the lectin. However, modification of tyrosine residue and carboxy group of the acidic amino acids led to a complete loss of its activity, indicating the involvement of tyrosine and aspartic and glutamic acid in the saccharide-binding respectively. The hemagglutinating activity of the lectin was completely/almost completely lost by modification of tryptophan residues. The relative loss in hemagglutinating activity on modification of tryptophan residues indicate that one residue/molecule is required for the carbohydrate-binding activity of the lectin. Modification was not effective in the presence of D-galactose (0.2 M). A marked decrease in the fluorescence emission was found as the tryptophan residues of crotalarin were modified. The c.d. spectra showed the presence of an identical pattern of conformation in the native and modified lectins which confirms that the loss in activity was due to modification only. The effect of periodate oxidation on crotalarin showed loss of activity whereas action of enzymes retained most of the activity.

Physicochemical studies of binding of 4-methylumbelliferyl beta-D-galactopyranoside to cold agglutinin

The fluorescence of 4-methylumbelliferyl beta-D-galactopyranoside (MeUmbGalp) was quenched in the presence of cold agglutinin, showing that there was binding between MeUmbGalp and cold agglutinin. That binding was saccharide-specific. By using this quenching phenomenon, the association constants (Ka) of the binding of cold agglutinin at different temperatures (10 degrees C and 15 degrees C) to MeUmbGalp and also the number of binding sites were calculated. The Ka values were found to be 2.63 x 10(3) M-1 at 10 degrees C and 1.58 x 10(3) M-1 at 15 degrees C. Though there is a change in Ka values, the number of binding sites was calculated to be six at both temperatures (10 degrees C and 15 degrees C). From the Ka values the thermodynamic parameters (free energy, enthalpy and entropy) of the binding were derived, and analysis of the data indicated that the binding is spontaneous, exothermic and hydrophobic in nature.