Carbohydrate recognition factors of a Talpha (Galbeta1-->3GalNAcalpha1-->Ser/Thr) and Tn (GalNAcalpha1-->Ser/Thr) specific lectin isolated from the seeds of Artocarpus lakoocha.
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 Galbeta1-->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 GalNAcalpha1-->Ser/Thr (Tn) and Galbeta1-->3 GalNAcalpha1-->Ser/Thr (Talpha). It barely cross-reacts with other common glycotopes on glycoproteins, including ABH blood group antigens, Galbeta1-->3/4GlcNAc (I/II) determinants, T/Tn covered by sialic acids, and N-linked plasma glycoproteins. Dense clustering structure of Tn/Talpha-containing glycoproteins tested resulted in 2.4 x 10(5)-6.7 x 10(5)-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/Talpha glycotopes >> monomeric Talpha and simple clustered Tn >> monomeric Tn > GalNAc > Gal; while other glycotopes: Galalpha1-->3/4Gal (B/E), Galbeta1-->3/4GlcNAc (I/II), GalNAcalpha1-->3Gal/GalNAc (A/F), and GalNAcbeta1-->3/4Gal (P/S) were inactive. The strong specificity of ALA for Tn/Talpha 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.
Singh
Tanuja
T
Glyco-Immunochemistry Research Laboratory, Institute of Molecular and Cellular Biology, Chang-Gung University, Kwei-san, Tao-yuan, 333, Taiwan.
Chatterjee
Urmimala
U
Wu
June H
JH
Chatterjee
Bishnu P
BP
Wu
Albert M
AM
D000107:Acetylation; D031622:Artocarpus / Q000378:metabolism*; D019921:Biotinylation; D005690:Galactose / Q000737:chemistry / Q000378:metabolism*; D006031:Glycosylation; D037121:Plant Lectins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D012639:Seeds / Q000378:metabolism*; D012694:Serine / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*
D037121:Plant Lectins; D011134:Polysaccharides; D013912:Threonine; D012694:Serine; D005690:Galactose