Interaction of a human blood group Sd(a-) Tamm-Horsfall glycoprotein with applied lectins

Recognition factors of Dolichos biflorus agglutinin (DBA) and their accommodation sites

Dolichos biflorus agglutinin (DBA) is one of the well known plant lectins that are widely used in clinical serology to differentiate human blood group A1 and A2 erythrocytes and also applied to glycobiology. However, the knowledge of recognition factors of polyvalent (super) glycotopes in glycans and the roles of functional group and epimer in monosaccharide (sub-monosaccharide recognition factor) have not been well established. The size and shape of the recognition (combining) site of DBA has not been clearly defined. In this study, many importnat recognition factors of DBA-glycan binding were characterized by our established enzyme-linked lectinosorbent (ELLSA) and inhibition assays. The results of these assays showed that the intensity profile of the recognition factors for the major combining site of DBA was expressed by Mass relative potency (Mass R.P.) and shown by decreasing order of high density of polyvalent GalNAcα1 → (super glycotopes, 3.7 × 103) >> the corresponding β anomers >> monomeric GalNAcα1 → related glycotopes (GalNAc as 1.0) >> their GalNAc β-anomers >> Gal (absence of NHCH3CO at carbon-2 of GAlNAc) and GlcNAc (different epimer of Carbon-4 in GalNAc). From the all data available, it is proposed that the combining site of DBA should consist of a small cavity shape as major site and most complementary to monomeric GalNAcα → located at both terminal reducing end (Tn) and nonreducing end of glycan chains, and with a wide and broad area as subsite to accomodate from mono- to tetra-saccharides (GalNAcβ, Galβ1 → 3/4GlcNAc, lFuc1 → 2Galβ1 → 3/4GlcNAc, GalNAcβ1 → 3Galα1 → 4Galβ1 → 4Glc) at the nonreducing side. In this study, it has provided the most (comprehensive) recognition knowledge of DBA-glycan interactions at the factors of glycotope, super glycotope/sub-monosaccharide levels. Thus, it should expand and upgrade the conventional concept of the combining (recognition) site of DBA since 1980s.

N-Glycans carried by Tamm-Horsfall glycoprotein have a crucial role in the defense against urinary tract diseases

Tamm-Horsfall glycoprotein (THGP), produced exclusively by renal cells from the thick ascending limb of Henle's loop, is attached by a glycosyl-phosphatidylinositol (GPI)-anchor to the luminal face of the cells. Urinary excretion of THGP (50-100 mg/day) occurs upon proteolytic cleavage of the large ectodomain of the GPI-anchored form. N-Glycans, consisting of a large repertoire of sialylated polyantennary chains and high-mannose structures, account for approximately 30% of the weight of human urinary THGP. We describe: (i) the involvement of urinary THGP high-mannose glycans in defense against infections of the urinary tract, caused by type-1 fimbriated Escherichia coli, which recognize high-mannose structures, (ii) the role of GalNAcbeta1-4(NeuAcalpha2-3)Galbeta1-4GlcNAcbeta1-3Gal (Sd(a) determinant) carried by human THGP in protecting the distal nephron from colonization of type-S fimbriated E. coli which recognise NeuAcalpha2-3Gal, (iii) the inhibitory effect of sialylated THGP on crystal aggregation of calcium oxalate and calcium phosphate, thus preventing nephrolithiasis. Finally, we outline the importance of N-glycans in promoting the polymerization of THGP, a process resulting in the formation of homopolymers with an M(r) of several million in urine. Since THGP defense against diseases of the urinary tract mainly consists in binding damaging agents, its ability to behave as a multivalent ligand significantly enhances this protective role.

Red blood cell antigens responsible for inherited types of polyagglutination

The three described types on inheritable polyagglutination are related to altered carbohydrate structures in glycoproteins or/and glycolipds on the erythrocyte surface. HEMPAS, a condition causing anemia and other pathological symptoms, is characterized by impaired biosynthesis of N-glycans, mostly those carried by band 3 and band 4.5 erythrocyte membrane proteins. Cad erythrocytes have abnormal glycophorin O-glycans, structurally related to the more common human Sd(a) and murine CT determinants, and accumulate an Sd(a)-like ganglioside. NOR erythrocytes express recently detected abnormal alpha-galactose-terminated glycosphingolipids, which strongly react with G. simplicifolia IB4 isolectin, but do not react with human anti-Galalpha1-3Gal antibodies.

Expression of binding properties of Gal/GalNAc reactive lectins by mammalian glycotopes (an updated report)

Expression of the binding properties of Gal/GalNAc specific lectins, based on the affinity of decreasing order of mammalian glycotopes (determinants) rather than monosaccharide inhibition pattern, is probably one of the best ways to express carbohydrate specifity and should facilitate the selection of lectins as structural probes for studying mammalian glycobiology. Eleven mammalian structural units have been selected to express the binding domain of applied lectins. They are: 1. F, GalNAcalpha1 --> 3GalNAc; 2. A, GalNAcalpha1 --> 3Gal; 3. T, Galbeta1 --> 3GalNAc; 4. I, Galbeta 1 --> 3GlcNAc; 5. II, Galbeta1 --> 4GlcNAc; 6. B, Galalpha1 --> 3Gal; 7. E, Galalpha1--> 4Gal; 8. L, Galbeta1 --> 4Glc; 9. P, GalNAcbeta1 --> 3Gal; 10. S, GalNAcbeta1 --> 4Gal and 11. Tn, GalNAcalpha1 --> 4Ser (Thr) of the peptide chain. Thus, the carbohydrate specificity of Gal/GalNAc reactive lectins can be divided into classes according to their highest affinity for the above disaccharides and/or Tn residue. Examples of the binding properties of these lectins can be demonstrated by Ricimus communis agglutinin (RCA1), grouped as II specific lectin and its binding property is II > I > B > T; Ahrus precatorius agglutinin (APA), classified as T and its carbohydrate specificity is T > I/II > E > B > Tn; Artocarpus integrifolia (jacalin, AIL), as T/Tn specific and its binding reactivity is T > Tn >> I (II) and Geodia cydonium (GCL), as F/A specific, and with affinity for F > Ah [GalNAcalpha1-->43(L(Fuc)alpha1-->2)Gal] >> I > L. Due to the multiple reactivity of lectins toward mammalian glycotopes, the possible existence of different combining sites or subsites in the same molecule has to be examined, and the differential binding properties of these combining sites (if any) have to be characterized. To establish the relationship among the amino acid sequences of the combining sites of plant lectins and mammalian glycotopes should be an important direction to be addressed in lectinology.

Analysis of the interaction between lectins and tetra- and tri-saccharide mimics of the Sd(a) determinant by surface plasmon resonance detection

The binding properties of a spacer-linked synthetic Sd(a) tetrasaccharide beta-D-GalpNAc-(1-->4)-alpha-Neu5Ac-(2-->3)]-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->O)-(CH(2))(5)-NH(2) (1), two tetrasaccharide mimics beta-D-Galp-(1-->4)-alpha-Neu5Ac-(2-->3)]-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->O)-(CH(2))(5)-NH(2) (2) and beta-D-GlcpNAc-(1-->4)-alpha-Neu5Ac-(2-->3)]-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->O)-(CH(2))(5)-NH(2) (3), and two trisaccharide mimics beta-D-GalpNAc-(1-->4)-3-O-(SO(3)H)-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->O)-(CH(2))(5)-NH(2) (4) and beta-D-GalpNAc-(1-->4)-3-O-(CH(2)COOH)-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->O)-(CH(2))(5)-NH(2) (5) with lectins from Dolichos biflorus (DBL), Maackia amurensis (MAL), Phaseolus limensis (PLL), Ptilota plumosa (PPL), Ricinus communis 120 (RCL120) and Triticum vulgaris (wheat germ agglutinin, WGA) have been investigated by surface plasmon resonance (SPR) detection. MAL, PPL, RCL120 and WGA did not display any binding activity with compounds 1-5. However, DBL and PLL, both exhibiting GalNAc-specificity, showed strong binding activity with compounds 1, 4 and 5, and 1, 3, 4 and 5, respectively. The results demonstrate that SPR is a very useful analysis system for identifying biologically relevant oligosaccharide mimics of the Sd(a) determinant.

Differential binding of human blood group Sd(a+) and Sd(a-) Tamm-Horsfall glycoproteins with Dolichos biflorus and Vicia villosa-B4 agglutinins

The binding patterns of human blood group Sd(a+) and Sd(a-) Tamm-Horsfall glycoproteins (THGPs) with respect to four GalNAc specific agglutinins were studied by quantitative precipitin assay (QPA) and enzyme linked lectinosorbent assay (ELLSA). Of the native and asialo Sd(a+) and Sd(a-) THGP tested by QPA and ELLSA, only native and asialo Sd(a+) bound well with Dolichos biflorus (DBA) and Vicia villosa-B4 (VVA-B4), while Sd(a-) THGP reacted poorly with these two lectins. Neither Sd(a+) nor Sd(a-) THGPs reacted with two other GalNAc alpha-anomer specific lectins: Codium fragile subspecies tomentosoides and Artocarpus integrifolia. Furthermore, the binding of asialo Sd(a+)THGP-VVA-B4 and native Sd(a+)THGP-DBA through GalNAc beta--> was confirmed by inhibition assay. These results demonstrate that DBA and VVA-B4 are useful reagents to differentiate between Sd(a+) and Sd(a-) THGP.

Further refinement of the description of the ligand-binding characteristics for the galactoside-binding mistletoe lectin, a plant agglutinin with immunomodulatory potency

The galactoside-binding lectin from mistletoe (Viscum album L.) is a biological response modifier, eliciting e.g. enhanced secretion of cytokines. This immunological activity warrants the further analysis of its ligand-binding properties with special attention paid to blood group epitopes. To avoid the microheterogeneity and complexity of naturally occurring glycoproteins, chemically strictly defined neoglycoconjugates and a panel of synthetic oligosaccharides were employed in solid-phase assays for direct binding and assessment of the relative inhibitory capacity. Since label incorporation into the lectin, although performed under protective conditions, or surface immobilization by adsorption to plastic may affect its affinity characteristics, the extent of neoglycoconjugate binding in the absence of any interfering substance and in the presence of oligosaccharides was determined comparatively with labeled and with immobilized lectin. In principle, these two factors could be excluded to markedly alter binding features. In addition to lactose, the blood group determinants H and B were strongly reactive. A fucose residue can thus especially be accommodated to the binding site when linked to the non-reducing unit. N-Acetyllactosamine was nearly as potent as an inhibitor as lactose. Lec and the A determinant were notably inferior to the other ABH blood group epitopes. Le(a) and Le(x) and their sialylated derivatives displayed only very weak binding capacity. Among the two natural isomers of sialyllactose, the alpha 2,6-form displayed a higher level of inhibitory capacity than the alpha 2,3-derivative. Isomeric variants of the Thomsen-Friedenreich antigen, too, reduced lectin binding to the lactose-carrying polymer. Their capacities were surpassed by those of the H and the B determinants and a related form of the latter, the P1 epitope. An overlap of specificity with the immunomodulatory human galectin-3 is thus measurable for H/B-like structures. The documented differential reactivity of the mistletoe lectin to blood group oligosaccharides may have a bearing on the responsiveness of blood group-positive cell populations.