Comparative cross-linking activities of lactose-specific plant and animal lectins and a natural lactose-binding immunoglobulin G fraction from human serum with asialofetuin.
Plant and animal lectins bind and cross-link certain multiantennary oligosaccharides, glycopeptides, and glycoproteins. This can lead to the formation of homogeneous cross-linked complexes, which may differ in their stoichiometry depending on the nature of the sugar receptor involved. As a precisely defined ligand, we have employed bovine asialofetuin (ASF), a glycoprotein that possesses three asparagine-linked triantennary complex carbohydrate chains with terminal LacNAc residues. In the present study, we have compared the carbohydrate cross-linking properties of two Lac-specific plant lectins, an animal lectin and a naturally occurring Lac-binding polyclonal immunoglobulin G subfraction from human serum with the ligand. Quantitative precipitation studies of the Lac-specific plant lectins, Viscum album agglutinin and Ricinus communis agglutinin, and the Lac-specific 16 kDa dimeric galectin from chicken liver demonstrate that these lectins form specific, stoichiometric cross-linked complexes with ASF. At low concentrations of ASF, 1:9 ASF/lectin (monomer) complexes formed with both plant lectins and the chicken lectin. With increasing concentrations of ASF, 1:3 ASF/lectin (monomer) complexes formed with the lectins irrespective of their source or size. The naturally occurring polyclonal antibodies, however, revealed a different cross-linking behavior. They show the formation of 1:3 ASF/antibody (per Fab moiety) cross-linked complexes at all concentrations of ASF. These studies demonstrate that Lac-specific plant and animal lectins as well as the Lac-binding immunoglobulin subfraction from specific stoichiometric cross-linked complexes with ASF. These results are discussed in terms of the structure-function properties of multivalent lectins and antibodies.
Gupta
D
D
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Kaltner
H
H
Dong
X
X
Gabius
H J
HJ
Brewer
C F
CF
D000818:Animals; D001212:Asialoglycoproteins / Q000378:metabolism*; D060748:Fetuins; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D007785:Lactose / Q000378:metabolism*; D028321:Plant Preparations; D010940:Plant Proteins; D010944:Plants / Q000378:metabolism*; D011233:Precipitin Tests; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological / Q000378:metabolism*; D000509:alpha-Fetoproteins / Q000378:metabolism*
D001212:Asialoglycoproteins; D060748:Fetuins; D007074:Immunoglobulin G; D028321:Plant Preparations; D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological; D000509:alpha-Fetoproteins; C017029:asialofetuin; C009674:ribosome inactivating protein, Viscum; D007785:Lactose