Glycobiology, 2000, Vol. 10, No. 9 891-900
© 2000 Oxford University Press
Carbohydrate groups of 
1-microglobulin are important for secretion and tissue localization but not for immunological properties
Section for Molecular Signalling, Department of Cell and Molecular Biology, Lund University, Lund, Sweden, 2Section for Tumour Immunology, Department of Cell and Molecular Biology, Lund University, Lund, Sweden, 3Department of Radiation Physics, The Jubileum Institute, Lund University, Lund, Sweden, and 4Haematology Research Laboratory, Department of Laboratory Medicine, Lund University, Lund, Sweden
The role of the carbohydrates for the structure and functions of the plasma and tissue protein 
1-microglobulin (1m) was investigated by deletion of the sites for N-glycosylation by site-directed mutagenesis (N17,96
Q). The mutated cDNA was expressed in a baculovirus-insect cell system resulting in a nonglycosylated protein. The biochemical properties of N17,96Q-1m were compared to nonmutated 1m, which carries two short non-sialylated N-linked oligosaccharides when expressed in the same system. Both proteins carried a yellow-brown chromophore and were heterogeneous in charge. Circular dichroism spectra and antibody binding indicated a similar overall structure. However, the secretion of N17,96Q-1m was significantly reduced and 
75% of the protein were found accumulated intracellularly. The in vitro immunological effects of recombinant nonmutated 1m and N17,96Q-1m were compared to the effects of 1m isolated from plasma, which is sialylated and carries an additional O-linked oligosaccharide. All three 1m variants bound to human peripheral lymphocytes and mouse T cell hybridomas to the same extent. They also inhibited the antigen-stimulated proliferation of peripheral lymphocytes and antigen-stimulated interleukin 2-secretion of T cell hybridomas in a similar manner. After injection of rats intravenously, the blood clearance of recombinant nonmutated and N17,96Q- 1m was faster than that of plasma 1m. Nonmutated 1m was located primarily to the liver, most likely via binding to asialoglycoprotein receptors, and N17,96Q-1m was located mainly to the kidneys. It is concluded that the carbohydrates of 1m are important for the secretion and the in vivo turnover of the protein, but not for the structure or immunological properties.
1 To whom correspondence should be addressed at: Section for Molecular Signalling, Department of Cell and Molecular Biology, P.O. Box 94, University of Lund, S-221 00 Lund, Sweden
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