Open Accessα3‐Galactosylated glycoproteins can bind to the hepaticasialoglycoprotein receptor
Author(s) -
Joziasse David H.,
Lee Reiko T.,
Lee Yuan C.,
Biessen Erik A. L.,
Schiphorst Wietske E. C. M.,
Koeleman Carolien A. M.,
van den Eijnden Dirk H.
Publication year - 2000
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.2000.01747.x
Subject(s) - lectin , glycoprotein , asialoglycoprotein receptor , glycan , biochemistry , sialic acid , oligosaccharide , chemistry , in vitro , orosomucoid , membrane glycoproteins , concanavalin a , receptor , galactose , hepatocyte
In mammals, clearance of desialylated serum glycoproteins to the liver is mediated by a galactose‐specific hepatic lectin, the ‘asialoglycoprotein receptor’. In humans, serum glycoprotein glycans are usually capped with sialic acid, which protects these proteins against hepatic uptake. However, in most other species, an additional noncharged terminal element with the structure Galα1→3Galβ1→4R is present on glycoprotein glycans. To investigate if α3‐galactosylated glycoproteins, just like desialylated glycoproteins, could be cleared by the hepatic lectin, the affinities of α3‐galactosylated compounds towards this lectin were determined using an in vitro inhibition assay, and were compared with those of the parent compounds terminating in Galβ1→4R. Diantennary, triantennary and tetraantennary oligosaccharides that form part of N ‐glycans were α3‐galactosylated to completion by use of recombinant bovine α3‐galactosyltransferase. Similarly, desialylated α 1 ‐acid glycoprotein (orosomucoid) was α3‐galactosylated in vitro . The α3‐galactosylation of a branched, Galβ1→4‐terminated oligosaccharide lowered its affinity for the membrane‐bound lectin on whole rat hepatocytes 50–250‐fold, and for the detergent‐solubilized hepatic lectin 7–50‐fold. In contrast, α3‐galactosylation of asialo‐α 1 ‐acid glycoprotein caused only a minor decrease in affinity, increasing the IC 50 from 5 to 15 n m . Fully α3‐galactosylated α 1 ‐acid glycoprotein, intravenously injected into the mouse, was rapidly cleared from the circulation, with a clearance rate close to that of asialo‐α 1 ‐acid glycoprotein ( t 1/2 of 0.42 min vs. 0.95 min). Its uptake was efficiently inhibited by pre‐injection of an excess asialo‐fetuin. Organ distribution analysis showed that the injected α 1 ‐acid glycoprotein accumulated predominantly in the liver. Taken together, these observations suggest that serum glycoproteins that are heavily α3‐galactosylated will be rapidly cleared from the bloodstream via the hepatic lectin. It is suggested that glycosyltransferase expression in murine hepatocytes is tightly regulated in order to prevent undesired uptake of hepatocyte‐derived, circulating glycoproteins.