Kinetics of binding of oligosaccharides to a homogeneous pneumococcal antibody: dependence on antigen chain length suggests a labile intermediate complex

Abstract

Temperature-jump experiments were performed with di-, tetra-, and hexasaccharides derived from type III pneumococcal polysaccharide using a homogeneous corresponding antibody IgG 45-394. A decrease in stability of the oligosaccharide-antibody complexes with decreasing chain length was observed and entirely reflected in the decrease of the association rate constants which were 1.7 X 10(4) M-1 s-1 for the di-, 3.7 X 10(5) M-1 s-1 for the tetra-, and 1.1 X 10(6) M-1 s-1 for the hexasaccharide at 23 degrees C. The dissociation rate constants for all oligomers were about 12 s-1. This marked chain-length dependence of the association rate constants as well as their low values are unexpected for a single binding step. A mechanism is proposed which consists of a fast formation of a labile oligosaccharide-antibody precomplex followed by a slow isomerization step which is induced by the oligosaccharide ligands but which is chain-length independent.

Analysis by Surface Plasmon Resonance of the Influence of Valence on the Ligand Binding Affinity and Kinetics of an Anti-carbohydrate Antibody

“…Presumably, this is typical of protein-carbohydrate interactions in general and is the reason for their low intrinsic affinities. Fluorescence (16) and NMR (17) methods have given on-rates for other proteincarbohydrate interactions that are similar to those reported here. These methods have also indicated that fast off-rates are responsible for the low affinities of protein-carbohydrate interactions and that differences in binding constants are primarily the result of differences in off-rates.…”

“…It is possible to obtain rate constants for protein-carbohydrate interactions by fluorescence (16) and NMR (17) methods, but these approaches are not generally applicable. Shinohara et al (18) demonstrated that SPR could be used to study the specificities of different lectins for various glycopeptides but did not attempt to analyze the contribution of lectin valence to observed rate constants.…”

Effect of Molecular Size on the Ability of Zwitterionic Polysaccharides to Stimulate Cellular Immunity

“…Up to hundreds of repeating units in the case of group B streptococcal and S. pneumoniae type 14 capsular polysaccharides are necessary to elicit optimal binding activity, thus supporting the hypothesis that anticapsular Abs recognize a conformational epitope fully expressed only in high m.w. forms of the T cell-independent saccharide molecules (21,24,40). Although six to seven sugar residues of a linear ␣(136)-linked glucose have been proven sufficient to fill the Ag-binding site of Igs (16 -18), such small-sized saccharides do not induce humoral response in primates.…”

High affinity anti‐carbohydrate antibodies identified in anti‐A‐variant streptococcal antisera

“…This can be illustrated by a specific example. The anti-S111 pneumococcal polysaccharide antibody 45394 possesses binding sites of intrinsic affinity 0.9-3.0 X 10' M-r [8] with a dissociation rate constant of 1 l-1 2 s-l. From the stability of its soluble antigen-antibody complexes, a dissociation rate constant for the complexes of -10-l s-l can be estimated [9] yielding an estimate of the overall association constant for antibody in the complex of 10" M-r. The SIII polysaccharide has mol.…”

“…Where quantitative data are available, an interesting generalization is apparent. The intrinsic affinities of antibody combining sites for fully complementary polysaccharide units lie in the range lo'--lo6 M-' [2,4,8]. In the course of screening rabbit anti-streptococcal group A-variant carbohydrate antibodies for antigen binding detectable by antibody fluorescence changes, several preparations were found to contain anti-polysaccharide antibodies of higher than average affinity (K, -10' M-l).…”