Mistletoe lectin I is a sialic acid-specific lectin with strict preference to gangliosides and glycoproteins with terminal Neu5Ac alpha 2-6Gal beta 1-4GlcNAc residues.
Mistletoe lectin I (ML-I) is a type II ribosome-inactivating protein, which inhibits the protein biosynthesis at the ribosomal level. ML-I is composed of a catalytically active A-chain with rRNA N-glycosidase activity and a B-chain with carbohydrate binding specificities. Using comparative solid-phase binding assays along with electrospray ionization tandem mass spectrometry, ML-I was shown to preferentially bind to terminally alpha2-6-sialylated neolacto series gangliosides from human granulocytes. IV(6)Neu5Ac-nLc4Cer, VI(6)Neu5Ac-nLc6Cer, and VIII(6)Neu5Ac-nLc8Cer were identified as ML-I receptors, whereas the isomeric alpha2-3-sialylated neolacto series gangliosides were not recognized. Only marginal binding of ML-I to terminal galactose residues of neutral glycosphingolipids with a Galbeta1-4Glc or Galbeta1-4GlcNAc sequence was determined, whereas a distal Galalpha1-4Gal, GalNAcbeta1-3Gal, or GalNAcbeta1-4Gal disaccharide did not bind at all. Among the glycoproteins investigated in Western blot and microwell adsorption assays, only those carrying Neu5Acalpha2-6Galbeta1-4GlcNAc residues, exclusively, predominantly, or even as less abundant constituents in an assembly with Neu5Acalpha2-3Galbeta1-4GlcNAc-terminated glycans, displayed high ML-I binding capacity. From our data we conclude that (i) ML-I has to be considered as a sialic acid- and not a galactose-specific lectin and (ii) neolacto series gangliosides and sialoglycoproteins with type II glycans, which share the Neu5Acalpha2-6Galbeta1-4GlcNAc terminus, are true ML-I receptors. This strict preference might help to explain the immunostimulatory potential of ML-I toward certain leukocyte subpopulations and its therapeutic success as a cytotoxic anticancer drug.
Müthing
Johannes
J
Institute for Medical Physics and Biophysics, University of Münster, Robert-Koch-Strasse 31, D-48149 Münster, Germany. jm@uni-muenster.de
Meisen
Iris
I
Bulau
Patrick
P
Langer
Martin
M
Witthohn
Klaus
K
Lentzen
Hans
H
Neumann
Ulrich
U
Peter-Katalinić
Jasna
J
D000327:Adsorption; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D001666:Binding Sites, Antibody; D002240:Carbohydrate Sequence; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004591:Electrophoresis, Polyacrylamide Gel; D005732:Gangliosides / Q000097:blood / Q000737:chemistry*; D006028:Glycosphingolipids / Q000097:blood / Q000737:chemistry; D006801:Humans; D037102:Lectins / Q000737:chemistry*; D008969:Molecular Sequence Data; D019158:N-Acetylneuraminic Acid / Q000097:blood / Q000737:chemistry; D036103:Nanotechnology; D009844:Oligosaccharides / Q000097:blood / Q000737:chemistry*; D010449:Peptide Mapping; D028321:Plant Preparations / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding; D054790:Ribosome Inactivating Proteins, Type 2; D012795:Sialoglycoproteins / Q000097:blood / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D014118:Toxins, Biological / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D028181:Viscum / Q000737:chemistry*
D000911:Antibodies, Monoclonal; D005732:Gangliosides; D006028:Glycosphingolipids; D037102:Lectins; D009844:Oligosaccharides; D028321:Plant Preparations; D010940:Plant Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D012795:Sialoglycoproteins; D014118:Toxins, Biological; C488862:mistletoe lectin I; C009674:ribosome inactivating protein, Viscum; C062923:N-acetylneuraminosyl(alpha2-6)lactosamine; D019158:N-Acetylneuraminic Acid