Glycobiology Advance Access originally published online on August 25, 2004
Glycobiology 2005 15(1):67-78; doi:10.1093/glycob/cwh144
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Glycobiology vol. 15 no. 1 © Oxford University Press 2005; all rights reserved.
Carbohydrate recognition factors of a T
(Galß1
3GalNAc
1
Ser/Thr) and Tn (GalNAc
1
Ser/Thr) specific lectin isolated from the seeds of Artocarpus lakoocha
2 Glyco-Immunochemistry Research Laboratory, Institute of Molecular and Cellular Biology, Chang-Gung University, Kwei-san, Tao-yuan, 333, Taiwan; 3 Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India; and 4 Department of Microbiology and Immunology, Chang-Gung University, Kwei-san, Tao-yuan, 333, Taiwan
1 To whom correspondence should be addressed; e-mail: amwu{at}mail.cgu.edu.tw
Received on June 7, 2004; revised on August 15, 2004; accepted on August 24, 2004
Artocarpus lakoocha agglutinin (ALA), isolated from the seeds of A. lakoocha fruit, is a galactose-binding lectin and a potent mitogen of T and B cells. Knowledge obtained from previous studies on the affinity of ALA was limited to molecular and submolecular levels of Galß1
3GalNAc (T) and its derivatives. In the present study, the carbohydrate specificity of ALA was characterized at the macromolecular level according to the mammalian Gal/GalNAc structural units and corresponding glycoconjugates by an enzyme-linked lectinosorbent (ELLSA) and inhibition assays. The results indicate that ALA binds specifically to tumor-associated carbohydrate antigens GalNAc
1
Ser/Thr (Tn) and Galß1
3 GalNAc
1
Ser/Thr (T
). It barely cross-reacts with other common glycotopes on glycoproteins, including ABH blood group antigens, Galß1
3/4GlcNAc (I/II) determinants, T/Tn covered by sialic acids, and N-linked plasma glycoproteins. Dense clustering structure of Tn/T
-containing glycoproteins tested resulted in 2.4 x 1056.7 x 105-fold higher affinities to ALA than the respective GalNAc and Gal monomer. According to our results, the overall affinity of ALA for glycans can be ranked respectively: polyvalent Tn/T
glycotopes >> monomeric T
and simple clustered Tn >> monomeric Tn > GalNAc > Gal; while other glycotopes: Gal
1
3/4Gal (B/E), Galß1
3/4GlcNAc (I/II), GalNAc
1
3Gal/GalNAc (A/F), and GalNAcß1
3/4Gal (P/S) were inactive. The strong specificity of ALA for Tn/T
cluster suggests the importance of glycotope polyvalency during carbohydratereceptor interactions and emphasizes its value as an anti-Tn/T lectin for analysis of glycoconjugate mixtures or transformed carbohydrates.
Key words: Artocarpus lakoocha / carbohydrate specificities / glycoprotein binding / lectins / polyvalency