Glycobiology Advance Access originally published online on February 8, 2008
Glycobiology 2008 18(4):331-338; doi:10.1093/glycob/cwn012
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Laminin-1 is a novel carrier glycoprotein for the nonsulfated HNK-1 epitope in mouse kidney
2 Department of Biological Chemistry, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto 606-8501
3 Department of Biological Chemistry, Human Health Science, Graduate School of Medicine, Kyoto University, Kyoto 606-8503
4 Division of Biological Chemistry and Biologicals, National Institute of Health Sciences, Tokyo 158-8501, Japan
1 To whom correspondence should be addressed: Tel: +81-75-751-3959; Fax: +81-75-751-3959; e-mail: shogo{at}hs.med.kyoto-u.ac.jp
Received on October 5, 2007; revised on January 14, 2008; accepted on February 2, 2008
The HNK-1 epitope has a unique structure comprising the sulfated trisaccharide (HSO3-3GlcAβ1-3Galβ1-4GlcNAc), and two glucuronyltransferases (GlcAT-P and GlcAT-S) are key enzymes for its biosynthesis. However, the different functional roles of these enzymes in its biosynthesis remain unclear. Recently, we reported that a nonsulfated form of this epitope, which is biosynthesized by GlcAT-S but not by GlcAT-P, is expressed on two metalloproteases in mouse kidney. In this study, we found that a novel glycoprotein carrying the nonsulfated HNK-1 epitope in mouse kidney was enriched in the nuclear fraction. The protein was affinity-purified and identified as laminin-1, and we also confirmed the N-linked oligosaccharide structure including nonsulfated HNK-1 epitope derived from laminin-1 by mass spectrometry. Curiously, immunofluorescence staining of kidney sections revealed that laminin-1 appeared not to be colocalized with the nonsulfated HNK-1 epitope. However, proteinase treatment strengthened the signals of both laminin-1 and the nonsulfated HNK-1 epitope, resulting in overlapping of them. These results indicate that the nonsulfated HNK-1 epitope on laminin-1 is usually embedded and masked in the robust basement membrane in tight association with other proteins. To clarify the associated proteins and the functional role of the carbohydrate epitope, we investigated the interaction between laminin-1 and alpha-dystroglycan through their glycans in mouse kidney using the overlay assay technique. We obtained evidence that glucuronic acid as well as sialic acid inhibited this interaction, suggesting that the nonsulfated HNK-1 epitope on laminin-1 may regulate its binding and play a role in maintenance of the proper structure in the kidney basal lamina.
Key words: Dystroglycan / glucuronyltransferase / HNK-1 / laminin
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