Kinetics of binding of oligosaccharides to a homogeneous pneumococcal antibody: dependence on antigen chain length suggests a labile intermediate complex.
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.
D000907:Antibodies, Bacterial; D001666:Binding Sites, Antibody; D007074:Immunoglobulin G / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D009844:Oligosaccharides / Q000276:immunology; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D011485:Protein Binding; D013296:Streptococcus pneumoniae / Q000276:immunology*; D013329:Structure-Activity Relationship; D013696:Temperature; D013816:Thermodynamics
D000907:Antibodies, Bacterial; D007074:Immunoglobulin G; D008024:Ligands; D009844:Oligosaccharides; D011135:Polysaccharides, Bacterial