Differential ligand binding by two subunits of the rat liver asialoglycoprotein receptor |
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Authors: | Ruiz, Nydia I. Drickamer, Kurt |
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Affiliation: | Departments of Biochemistry and Molecular Biophysics, Columbia University New York, NY 10032, USA |
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Abstract: | ![]() The rat liver asialoglycoprotein receptor consists of two typesof subunits, a predominant polypeptide designated rat hepaticlectin 1 (RHL-1) and a minor polypeptide, RHL-2/3, that comesin two differentially glycosylated forms. The exact stoichiometryand arrangement of the subunits in the RHL oligomer are notknown. The carbohydrate-recognition domain of RHL-2/ has beenprepared by limited proteolysis of the liver receptor so thatits properties can be compared with those of the correspondingdomain of RHL-1 previously produced in a bacterial expressionsystem. Binding studies indicate that while RHL-1 binds N-acetylgalactosaminewith approximately 60-fold higher affinity than it binds galactose,RHL-2/ has only 2-fold selectivity for N-acetylgalactosamine.In general, the pattern of monosaccharide-binding specificityfor RHL-2/ is similar to RHL-1, but the discrimination of varioussugars relative to galactose is reduced substantially. Limitedproteolysis and crosslinking studies demonstrate that RHL- 2/is easily removed from the RHL oligomer in detergent solutionand that RHL-1 remains at least trimeric following removal ofRHL-2/. These studies suggest that RHL-1 forms a ligand-bindingcore while RHL-2/ acts more as an accessory subunit contributingto selective binding of certain oligosaccharide structures. asialoglycoprotein receptor binding carbohydrate recognition lectin proteolysis |
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