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Glycobiology Advance Access published online on August 25, 2004
Glycobiology, doi:10.1093/glycob/cwh144
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Received June 7, 2004
Revised August 15, 2004
Accepted August 24, 2004

ORIGINAL ARTICLES

Carbohydrate recognition factors of a T{alpha} (Gal{beta}1->3GalNAc{alpha}1->Ser/Thr) and Tn (GalNAc{alpha}1->Ser/Thr) specific lectin isolated from the seeds of Artocarpus lakoocha

Tanuja Singh 1, Urmimala Chatterjee 2, June H. Wu 3, Bishnu P. Chatterjee 2, Albert M. Wu 1*

1 Glyco-Immunochemistry Research Laboratory, Institute of Molecular and Cellular Biology, Chang-Gung University, Kwei-san, Tao-yuan, 333, Taiwan
2 Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India
3 Department of Microbiology and Immunology, Chang-Gung University, Kwei-san, Tao-yuan, 333, Taiwan

* To whom correspondence should be addressed. E-mail: amwu{at}mail.cgu.edu.tw.


  Abstract

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 Gal{beta}1->3GalNAc (T) and its derivatives. In the present study, the carbohydrate specificity of ALA was characterized at 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{alpha}1->Ser/Thr (Tn) and Gal{beta}1->3 GalNAc{alpha}1->Ser/Thr (T{alpha}). It barely cross-reacts with other common glycotopes on glycoproteins, including ABH blood group antigens, Gal{beta}1->3/4GlcNAc (I/II) determinants, T/Tn covered by sialic acids and N-linked plasma gps. Dense clustering structure of Tn/T{alpha} containing glycoproteins tested resulted in 2.4x105-6.7x105 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{alpha} glycotopes >> monomeric T{alpha} and simple clustered Tn >> monomeric Tn > GalNAc > Gal; while other glycotopes: Gal{alpha}1->3/4Gal (B/E), Gal{beta}1->3/4GlcNAc (I/II), GalNAc{alpha}1->3Gal/GalNAc (A/F) and GalNAc{beta}1->3/4Gal (P/S) were inactive. The strong specificity of ALA for Tn/T{alpha} cluster suggests the importance of glycotope polyvalency during carbohydrate-receptor interactions and emphasizes its value as an anti-Tn/T lectin for analysis of glycoconjugate mixtures or transformed carbohydrates.

Keywords: Polyvalency; Carbohydrate specificities; Glycoprotein binding; Lectins; Artocarpus lakoocha.
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