Binding of the Wheat Germ Lectin to Cryptococcus neoformans Suggests an Association of Chitinlike Structures with Yeast Budding and Capsular Glucuronoxylomannan

ABSTRACT The capsule of Cryptococcus neoformans is a complex structure whose assembly requires intermolecular interactions to connect its components into an organized structure. In this study, we demonstrated that the wheat germ agglutinin (WGA), which binds to sialic acids and β-1,4-N-acetylglucosamine (GlcNAc) oligomers, can also bind to cryptococcal capsular structures. Confocal microscopy demonstrated that these structures form round or hooklike projections linking the capsule to the cell wall, as well as capsule-associated structures during yeast budding. Chemical analysis of capsular extracts by gas chromatography coupled to mass spectrometry and high-pH anion-exchange chromatography suggested that the molecules recognized by WGA were firmly associated with the cell wall. Enzymatic treatment, competition assays, and staining with chemically modified WGA revealed that GlcNAc oligomers, but not sialic acids, were the molecules recognized by the lectin. Accordingly, treatment of C. neoformans cells with chitinase released glucuronoxylomannan (GXM) from the cell surface and reduced the capsule size. Chitinase-treated acapsular cells bound soluble GXM in a modified pattern. These results indicate an association of chitin-derived structures with GXM and budding in C. neoformans, which may represent a new mechanism by which the capsular polysaccharide interacts with the cell wall and is rearranged during replication.

Carbohydrate characterization of purified thyroxine-binding globulin by lectin blot and isoelectric focusing

The structure of carbohydrate moiety of purified thyroxine-binding globulin (TBG) was examined by lectin blot and isoelectric focusing (IEF). In lectin blot, TBG reacted positively with the following lectins: Sambucus nigra agglutinin (SNA I), Ricinus commuais agglutinin (RCA I), wheat germ lectin (WGA), phytoheamagglutinin (PHA) and pea lectin (PSA). The obtained results indicate that purified TBG contains N-linked oligosaccharide chains consisting of mannose, galactose, N-acetylglucosamine and sialic acid. Isoelectric focusing of TBG at pl 4.2-4.6 revealed three bands, which confirmed that isolated TBG had retained its structure with?out desialylation. Lectin blot analysis and IEF can be considered to be useful tools in the study of TBG glycosylation.

Effects of a panel of dietary lectins on cholecystokinin release in rats

We previously showed that soybean lectin (SBL) releases cholecystokinin (CCK) and have now asked whether other dietary lectins have this effect and if extracellular calcium is involved. Lectins and vehicle were first infused into the duodenum of anesthetized rats. The CCK response to vehicle was 3.1 ± 0.6 pmol/l ( P < 0.05 vs. basal). SBL and peanut lectin (PNL) (84 μg/ml) significantly increased plasma CCK concentrations from 2.0 ± 0.4 pmol/l to a maximum of 8.4 ± 0.5 pmol/l ( P < 0.01 vs. vehicle, mean ± SE) and from 1.9 ± 0.5 to 7.0 ± 0.6 pmol/l ( P < 0.05 vs. vehicle, mean ± SE), respectively. Wheat germ lectin (WGL) (840 μg) also increased plasma CCK levels from 1.5 ± 0.3 pmol/l to a maximum of 9.7 ± 1.3 pmol/l ( P < 0.05 vs. vehicle, mean ± SE). Corresponding increases in pancreatic protein output occurred. Broad bean lectin (BBL) had no effect on either parameter. Dose-dependent responses were seen with SBL, PNL, and WGL (1, 10, and 100 μg/ml) in perifused rat intestinal cells. These responses were abolished in calcium-free medium and in the presence of the competing sugars of the lectins. Therefore, SBL, PNL, and WGL, which bind to motifs including N-acetyl-d-galactosamine, galactose, and N-acetylglucosamine, respectively, released CCK, but BBL, which binds to mannose and glucose, did not. Ingestion of lectins may have major CCK-mediated effects on gastrointestinal function and growth.