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Juvenile rheumatoid arthritis is associated with decreased activity of lectins that bind mannose and N-acetylgalactosamine

INTRODUCTION: Over a half of all known proteins contain covalently linked oligosaccharide structures that presumably perform some specific physiological functions (1). Due to the lack of adequate methods, until recently only little was known about the role of oligosaccharide structures of glycoconjugates, but in the recent years it was convincingly demonstrated that at least some of these structures are of utmost importance. One of the principal ways how oligosaccharides perform their functions is through interactions with their specific receptors named lectins. Recently we have developed glycoprobes (2), a novel set of compounds that enable direct measurement of lectin activity in complex biological samples. MATERIALS AND METHODS: The glycoprobe (Fig 1.) consists of three vital parts: (i) glycan; (ii) digoxin tag; and (iii) photoreactive crosslinker. When incubated in dark, oligosaccharide part of the glycoprobe forms a complex with lectin. After illumination, covalent link between the probe and the lectin is formed resulting in a digoxin-tagged lectin. Using antibodies against digoxin, this complex can easily be identified by Western blots. Glycoprobes containing Man9 oligosaccharide and Yee(ahGalNAc)3 glycopeptide were prepared as described (2) and used to analyze lectin activity in sera of 20 patients with juvenile rheumatoid arthritis and 20 control sera. Human serum proteins (75 ěg) were incubated in the presence of 0.8 mM mannose- or GalNAc-bioprobe in dark for 60 min. After crosslinking by UV-illumination, proteins were separated by 8% SDS PAGE, transferred onto PVDF membranes and analyzed with anti-digoxin antibodies. RESULTS: Using mannose- and GalNAc-containing glycoprobes we have analyzed activity of corresponding lectins in human serum. As expected, we were able to detect several lectins that specifically bound glycoprobes. The variability of lectin content and activity was surprisingly high in both patients with juvenile rheumatoid arthritis and controls. Some of the changes were apparently the consequence of natural variability, but for several specific lectins (Fig 2) we were able to demonstrate statistically significant differences between the control group and patients suffering from juvenile rheumatoid arthritis. 1. Apweiler R. (1999) BBA 1473:4-8. 2. Lauc G. (2000) Glycobiology 10:357-364.

juvenile rheumatoid arthritis; lectins

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