* To whom correspondence should be addressed.
Received January 13, 2011; Revision received March 1, 2011
Placenta is a source of carbohydrate-binding proteins that function as molecular scavengers, but they could also be involved in interactions that assist in metabolic control. Mannose/N-acetyl-glucosamine (Man/GlcNAc)-binding proteins from placenta were isolated and their reactivity towards placental insulin and insulin-like growth factor receptors (IR and IGF-Rs) was analyzed. The lectins reduced the binding of insulin and IGF-I in a dose-dependent manner, while almost no effect was observed on the binding of IGF-II. The shape of the inhibition curves changed, suggesting altered binding specificity. The presence of sugar could not reverse completely the effect of the lectins, implicating both lectin–sugar and protein–protein conformational recognition. Since biological molecules in our experimental system were those that are in close relation in vivo, placental Man/GlcNAc-specific lectins may be regarded as potential allosteric modulators of ligand–receptor interactions in a system of homologous ligands, selectively affecting only binding to tyrosine kinase type receptors (IR and IGF-1R).
KEY WORDS: insulin, insulin-like growth factors, receptors, lectins, placenta