Glycobiology vol 7 no 1 pp. 23-29, 1997
© 1997
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Characterization of a putative 82 kDa nuclear ligand for the N-acetylglucosamine-binding protein CBP70
Laboratoire de Glycobiologie et Reconnaissance Cellulaire, INSERM U180, UFR Biomédicale des Saints-Pères (Université René-Descartes Paris V) 45, rue des Saints-Pères, 75270 Paris Cedex 06, France
1Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität Duesbergweg 6, D-55099 Mainz Germany
2To whom correspondence should be addressed
Received on March 15, 1996; revised on August 2, 1996; accepted on August 11, 1996
Since nuclear lectins were first characterized several years ago, six lectins have been isolated. Furthermore, the existence of nuclear glycoproteins containing N-linked cornplex-oligosaccharide chains or O-linked GlcNAc residues was evidenced. These latter are abundant in the nucleus and are well-studied so far. The presence of both glycoprotein and lectin in the cell nucleus led us to postulate that these two proteins could interact and play a role in some nuclear activities such as the modulation of transcription and/or nuclear cytoplasmic exchanges or by the disruption of protein-protein interactions. In such context, the recent data concerning the GlcNAc-binding activity of CBP70 argued this postulate. However, to study the possible role of a glycoprotein-lectin complex, it was critical to isolate the two partners. Because CBP70 was also a cytoplasmic protein, the lectin was isolated in both cytoplasmic and nuclear compartments in order to investigate the putative ligand in the two cellular compartments. The results obtained with cross-linking experiments on isolated and membrane-depleted nuclei incubated with the CBP70 bearing an iodinatable, cleavable, photoreactive cross-linking agent (sulfosuccinimidyl 2-(p-azidosalicylamido) ethyl-1,3'-dithiopropionate) and immunoprecipitation experiments with polyclonal antibodies raised against CBP70, revealed that both nuclear and cytoplasmic CBP70 have the same 82 kDa nuclear ligand which is absent in the cytoplasmic fraction. In addition, this ligand is glycosylated, containing GlcNAc residues, and, therefore, the complex between CBP70 and the 82 kDa polypeptide could be due to a glycoprotein-lectin interaction. These results raised the possibility that nuclear glycoprotein-lectin interaction could be involved in nuclear activities.
nucleus lectins glycoproteins
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