Topography of the combining region of a Thomsen-Friedenreich-antigen-specific lectin jacalin (Artocarpus integrifolia agglutinin). A thermodynamic and circular-dichroism spectroscopic study

Abstract

Thermodynamic analysis of carbohydrate binding by Artocarpus integrifolia (jackfruit) agglutinin (jacalin) shows that, among monosaccharides, Me alpha GalNAc (methyl-alpha-N-acetylgalactosamine) is the strongest binding ligand. Despite its strong affinity for Me alpha GalNAc and Me alpha Gal, the lectin binds very poorly when Gal and GalNAc are in alpha-linkage with other sugars such as in A- and B-blood-group trisaccharides, Gal alpha 1-3Gal and Gal alpha 1-4Gal. These binding properties are explained by considering the thermodynamic parameters in conjunction with the minimum energy conformations of these sugars. It binds to Gal beta 1-3GalNAc alpha Me with 2800-fold stronger affinity over Gal beta 1-3GalNAc beta Me. It does not bind to asialo-GM1 (monosialoganglioside) oligosaccharide. Moreover, it binds to Gal beta 1-3GalNAc alpha Ser, the authentic T (Thomsen-Friedenreich)-antigen, with about 2.5-fold greater affinity as compared with Gal beta 1-3GalNAc. Asialoglycophorin A was found to be about 169,333 times stronger an inhibitor than Gal beta 1-3GalNAc. The present study thus reveals the exquisite specificity of A. integrifolia lectin for the T-antigen. Appreciable binding of disaccharides Glc beta 1-3GalNAc and GlcNAc beta 1-3Gal and the very poor binding of beta-linked disaccharides, which instead of Gal and GalNAc contain other sugars at the reducing end, underscore the important contribution made by Gal and GalNAc at the reducing end for recognition by the lectin. The ligand-structure-dependent alterations of the c.d. spectrum in the tertiary structural region of the protein allows the placement of various sugar units in the combining region of the lectin. These studies suggest that the primary subsite (subsite A) can accommodate only Gal or GalNAc or alpha-linked Gal or GalNAc, whereas the secondary subsite (subsite B) can associate either with GalNAc beta Me or Gal beta Me. Considering these factors a likely arrangement for various disaccharides in the binding site of the lectin is proposed. Its exquisite specificity for the authentic T-antigen, Gal beta 1-3GalNAc alpha Ser, together with its virtual non-binding to A- and B-blood-group antigens, Gal beta 1-3GalNAc beta Me and asialo-GM1 should make A. integrifolia lectin a valuable probe for monitoring the expression of T-antigen on cell surfaces.

Carbohydrate binding specificity of the Tn‐antigen binding lectin from Vicia villosa seeds (VVLB4)

“…This, together with the conformational analyses of these disaceharides, suggests a plausible mechanism of its preference for teminal fl-linked GalNAe and Gel structures which is as follows: in GalNAc(~xl-3)Gal, Gal(:zl-3)Gel the orientation of the sugar rings is such that they form a bent L-shaped structure in which the subterminal Gel is in close proximity to the terminal sugar preventing the entry of the latter in the combining site of the lectin [19]. Similar reasoning would also explain the non-binding of VYLB4 to blood group A.erythrocytes [5].…”

“…GalNDns was synthesized as described earlier [11,12]. Gal(0~l-3)Gal and Galtfll-3)GalNAe were prepared as in [19]. MectGalNAc and MeflGalNAc were prepared according to the method of Sarkar and Kabat [13].…”

The amino acid sequences of jacalin and the Maclura pomifera agglutinin

“…The structure of the jacalin glycopeptide has been reported [12] . Tyrosine residues are also implicated in the site [ 13], hence the ~t-ch ain Trp-123 appears more likely, since Tyr-122 and Tyr.126 are close to it. Though the carbohydrate specificities of the two proteins are very similar, there are some differences in their binding-site properties, MPA has a K, for methyl <z-Dgalactoside that is half the jacalin value and the change in intrinsic fluorescence on sugar binding is twice as large [1].…”

T-antigen (Gal β3 GaINAc α-) containing glycoproteins of human reace

“…The jacalinglycoprotein interaction was found to be sugar specific as it could be inhibited in the presence of 0.1M galactose. Investigations of jacalin's ligand specificity revealed its high affinty for ec-galactopyranosides and particularly for the T-antigen with the structure, 1-J~-D-galactopyra nosyl-3-(o~-2-acetamido-2-deoxygalactopyranoside) (13,14). Jacalin recognizes the T-antigenic structure on glycoproteins even when substituted with a terminal sialic acid residue (15).…”