Two
carbohydrate-
binding proteins with subunit molecular weight of about 17,500 and 16,500, respectively, were isolated from
Triton X-100 extracts of rat kidney using a
lactose affinity column. They did not require Ca2+ for the
carbohydrate-binding nor
reducing agents for maintaining their activity. The partial amino acid sequence of the 17.5-kDa
protein (rkCBP-17.5), the main component, revealed that this
protein is a novel member of a superfamily of
beta-galactoside-binding
animal lectins. The N-terminal amino acid sequence of the 16.5 kDa component (rkCBP-16.5) indicated that it is a fragment derived from the
IgE-binding protein (
IgEBP).
Monoclonal antibodies to rkCBP-17.5 were prepared and used to examine the distribution of the
lectin in various organs of adult rats. Immunoreactive
protein with the same molecular weight was found in lung, spleen and liver, in lesser amounts in heart, and in trace amounts in brain and skeletal muscle. rkCBP-17.5 exhibits binding activity to various saccharides with the following order of affinity:
N-acetyllactosamine >
lactose >
D-galactose >
methyl alpha-D-galactopyranoside >
N-acetyl-D-galactosamine >
methyl beta-D-galactopyranoside. It binds to Engelbreth-Holm-Swarm(
EHS) tumor laminin and rat plasma
fibronectin, but does not bind to human plasma
fibronectin.