title: Sialic acid specificity of myelin-associated glycoprotein binding.
abstract: Myelin-associated glycoprotein (MAG), a nervous system cell adhesion molecule, is an I-type lectin that binds to sialylated glycoconjugates, including gangliosides bearing characteristic structural determinants (Yang, L. J.-S., Zeller, C. B., Shaper, N. L., Kiso, M., Hasegawa, A., Shapiro, R. E., and Schnaar, R. L. (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 814-818). Two cell adhesion systems, COS-1 monkey kidney fibroblasts transiently transfected to express MAG and Chinese hamster ovary (CHO) cells stably transfected to express MAG, were used to probe the structural specificity of MAG-ganglioside binding. Both cell types bound to the same gangliosides: GQ1b alpha (IV3NeuAc,III6NeuAc,II3(NeuAc)2Gg4Cer) > GT1b = GD1a > GM3 > GM1, GD1b, and GQ1b (the latter do not support adhesion). Binding was enhanced by pretreatment of MAG-expressing cells with neuraminidase. MAG-expressing Chinese hamster ovary cells bound directly to gangliosides resolved on thin layer chromatograms, allowing detection of MAG binding species in a mixture. The simplest ganglioside ligand for MAG was GM3 bearing N-acetylneuraminic acid, whereas GM3 bearing N-glycolylneuraminic acid did not support adhesion. Chemical modifications of N-acetylneuraminic acid residues (on GD1a) abrogated MAG binding. Mild periodate oxidation of sialic acids to their corresponding seven-carbon (or eight-carbon) sialic acid aldehydes abolished MAG binding, as did further conversion to the corresponding primary alcohols. Eliminating the anionic charge by ethyl esterification, amidation, or reduction also abolished MAG-mediated cell adhesion. These data demonstrate that MAG-ganglioside binding is highly specific and defines key carbohydrate structural determinants for MAG-mediated cell adhesion to gangliosides.
authors.affiliation: Department of Pharmacology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: B E
authors.initials: BE
authors.lastname: Collins
authors.forename: L J
authors.initials: LJ
authors.lastname: Yang
authors.forename: G
authors.initials: G
authors.lastname: Mukhopadhyay
authors.forename: M T
authors.initials: MT
authors.lastname: Filbin
authors.forename: M
authors.initials: M
authors.lastname: Kiso
authors.forename: A
authors.initials: A
authors.lastname: Hasegawa
authors.forename: R L
authors.initials: RL
authors.lastname: Schnaar
mesh_terms: D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002448:Cell Adhesion; D006224:Cricetinae; D003412:Cricetulus; D005732:Gangliosides / Q000378:metabolism; D000882:Haplorhini; D018992:Myelin-Associated Glycoprotein / Q000378:metabolism*; D019158:N-Acetylneuraminic Acid / Q000378:metabolism*; D009439:Neuraminidase / Q000378:metabolism; D013379:Substrate Specificity; D014162:Transfection; D014733:Vibrio
chemical_list: D005732:Gangliosides; D018992:Myelin-Associated Glycoprotein; C021298:ganglioside, GD1a; D009439:Neuraminidase; D019158:N-Acetylneuraminic Acid