HIGH AFFINITY LIGANDS FOR HUMAN LYMPHOCYTE RECEPTOR CD69
Jiří Pavlíček1, Rüdiger Ettrich2, Petr Novák3,Petr Man1,3, Jana Vodrážková1 and Karel Bezouška1,3
1 Department of Biochemistry, Faculty of Science, Charles University in Prague, Hlavova 8, CZ-12840 Praha 2, Czech Republic; 2Laboratory of High Performance Computing, Institute of Physical Biology USB and Institute of Landscape Ecology AS CR, Zámek 136, CZ-37333 Nové Hrady, Czech Republic; 3 Institute of Microbiology, Academy of Sciences of the Czech Republic, CZ-14220 Praha 4, Czech Republic
CD69 is one of very important activating receptors expressed on the surface of human lymphocytes. This molecule exists as a homodimer, each of its subunits being terminated with the globular domain related to the C-type lectin family. Although the crystal structure of this domain has been recently solved , its potential ligands and the function of the whole receptor remain unclear. In our laboratory  we established that calcium ion can be bound tigtly in the molecule and this binding increases the affinity of the protein to N-acetylglucosamine and N-acetylgalactosamine. The positions of binding sites has been suggested by molecular modeling and proved by site-directed mutagenesis.
These data allowed us to find potential high affinity ligands among branched oligosaccharides terminated with N-acetylglucosamine units. We isolated these molecules by deglycosylation of ovomucoid and characterized them by mass spectrometry. From results of our binding studies we can conclude that pentaantenary structure is the ligand with the highest known affinity for CD69 molecule. It has been published [3, 4] that similar structures are expressed on the surface of some tumor cells. This finding indicates that one role of CD69 molecule on the cells of the immune system may be to attract killer lymphocytes to the tumor sites.
Acknowledgement: This work was supported by Institutional Research Concept No. AV0Z5020903 (for Institut of Microbiology) and by grants MSM 113100001, GAČR 203/01/1018 and A7020006.
 S. Natarajan et al., Biochemistry, 39 (2000) 14779–14786.
 K. Bezouška et al. BBRC, 208 (1995) 68-74.
 J. W. Dennis et al. Science, 236 (1987) 582-585.
 E. Gorelik et al. Cancer and Metastasis Reviews, 20 (2001) 245-277.