Fusarium sp. growth inhibition by wheat germ agglutinin.

The antifungal role of wheat germ agglutinin (WGA) isolated from a Romanian dihaploid variety of wheat against two pathogenic fungal species of Fusarium, F. graminearum and F. oxysporum, is demonstrated. WGA was prepared from unprocessed wheat germs by a new purification procedure using chitin and fetuin-Sepharose as affinity chromatography supports. SDS-PAGE and chitinase assay showed that the WGA preparation migrated as a single protein band and was devoid of any contaminating enzyme chitinase, well known for its antifungal effects. Based on its affinity for N-acetylglucosamine residues, WGA binding to the chitin-containing walls of the fungi was detected by fluorescence microscopy using WGA coupled with fluorescein isothiocyanate (FITC). In vitro testing of WGA action on early developmental stages of both fungal strains resulted in various modifications of the germ tubes, visualised by light microscopy: swelling, vacuolation of the cellular content and lysis of cell walls. Viability tests performed on potato tuber slices showed that the microbial infection was prevented from spreading by pretreatment of the fungal suspension with WGA.

Isolectins from Solanum tuberosum with different detailed carbohydrate binding specificities: unexpected recognition of lactosylceramide by N-acetyllactosamine-binding lectins.

Glycosphingolipid recognition by two isolectins from Solanum tuberosum was compared by the chromatogram binding assay. One lectin (PL-I) was isolated from potato tubers by affinity chromatography, and identified by MALDI-TOF mass spectrometry as a homodimer with a subunit molecular mass of 63,000. The other (PL-II) was a commercial lectin, characterized as two homodimeric isolectins with subunit molecular masses of 52,000 and 55,000, respectively. Both lectins recognized N-acetyllactosamine-containing glycosphingolipids, but the fine details of their carbohydrate binding specificities differed. PL-II preferentially bound to glycosphingolipids with N-acetyllactosamine branches, as Galbeta4GlcNAcbeta6(Galbeta4GlcNAcbeta3)Galbeta4Glcbeta1C er. PL-I also recognized this glycosphingolipid, but bound equally well to the linear glycosphingolipid Galbeta4GlcNAcbeta3Galbeta4GlcNAcbeta3Galbeta4Glcbeta1Cer. Neolactotetraosylceramide and the B5 pentaglycosylceramide were also bound by PL-I, while other glycosphingolipids with only one N-acetyllactosamine unit were non-binding. Surprisingly, both lectins also bound to lactosylceramide, with an absolute requirement for sphingosine and non-hydroxy fatty acids. The inhibition of binding to both lactosylceramide and N-acetyllactosamine-containing glycosphingolipids by N-acetylchitotetraose suggests that lactosylceramide is also accomodated within the N-acetylchitotetraose/N-acetyllactosamine-binding sites of the lectins. Through docking of glycosphingolipids onto a three-dimensional model of the PL-I hevein binding domain, a Galbeta4GlcNAcbeta3Galbeta4 binding epitope was defined. Furthermore, direct involvement of the ceramide in the binding of lactosylceramide was suggested.

Inhibition of saliva-induced oral streptococcal aggregation by blood group glycoproteins.

The inhibition of saliva-induced oral streptococcal aggregation with anti-sera (anti-A, anti-B, anti-AB and anti-B treated with galactose), normal human serum (NHS), blood group-specific lectins (UEA-I, HBA, GPA, BSI-B4, GS-I), non-specific blood group lectins (MPA, SBA) and carbohydrates (galactose, N-acetylgalactosamine, L-fucose) was studied. Streptococcal species and strains included S. mutans 318, S. mutans 10449, S. mutans NG-8, S. salivarius and S. cricetus HS-6. The saliva was obtained from three subjects with secretor status (2 blood group B persons, 1 blood group A person). The data obtained from experiments performed with S. mutans 10449 and S. mutans NG-8 suggest the involvement of the H-antigenic determinant in the aggregation mechanism of the first strain and of the group B determinant for the second strain. The aggregation of S. salivarius only by B saliva might be related to a galactose-specific lectin on this strain and to some properties of its cell surface (hydrophobicity and the fibrillar surface layer). S. cricetus HS-6 aggregation was inhibited in different degrees by all the inhibitors used. The results demonstrate that interactions between oral streptococci and salivary components depend on the strain and species and on the individual saliva samples.

Binding of the galactose-specific Pseudomonas aeruginosa lectin, PA-I, to glycosphingolipids and other glycoconjugates.

The carbohydrate-binding specificity of Pseudomonas aeruginosa lectin I (PA-I) in iodinated or biotinylated form was studied. A large number of glycosphingolipids, as well as some glycoproteins and neoglycoproteins were used as ligands. Also, inhibition by free saccharides of PA-I binding to glycosphingolipids was tested. It was found that the lectin binds most strongly to terminal and nonsubstituted Gal alpha 3Gal- or Gal alpha 4Gal-structures.

Antifungal properties of lectin and new chitinases from potato tubers.

We have purified from potato tubers, the lectin STA devoid of chitinase activity and two chitinases devoid of lectin activity. Both enzymes are 16 kDa glycoproteins, and probably belong to a new family of plant chitinases. The respective antifungal properties of lectin and chitinases were studied by following their effects against early developmental stages of Fusarium oxysporum, a fungal potato pathogen. Here we demonstrate that: (1) lectin does not inhibit mycelial growth but irreversibly inhibits conidia germination and alters the germ tubes; and (2) chitinases block mycelial growth as well as conidia germination and lyse germ tubes.