Oligomannosides or oligosaccharide-lipids as potential substrates for rat liver cytosolic α-D-mannosidase
Résumé
We have previously reported the substrate specificity of the cytosolic α--mannosidase purified from rat liver using Man * GlcNAc, i.e. Manα1-2Manα1-3(Manα1-2Manα1-6)Man α1-6(Manα1-2Manα1-2Manα1-3)Manβ1-4GlcNAc, as substrate [Grard, Saint-Pol, Haeuw, Alonso, Wieruszeski, Strecker and Michalski (1994) Eur. J. Biochem. 223, 99-106]. Man * GlcNAc is hydrolysed giving Man & GlcNAc, i.e. Manα1-2Manα1-2Manα1-3(Manα1-6)Manβ1-4GlcNAc, possessing the same structure as the oligosaccharide of the dolichol pathway formed in the cytosolic compartment during the biosynthesis of N-glycosylprotein glycans. We study here the activity of the purified cytosolic α--mannosidase towards the oligosaccharidediphosphodolichol intermediates formed during the biosynthesis Abbreviations used : P-P-Dol, diphosphodolichol ; Man 9 GlcNAc 2-P-P-Dol, Manα1-2Manα1-3(Manα1-2Manα1-6)Manα1-6(Manα1-2Manα1-2Manα1-3)Manβ1-4GlcNAcβ1-4GlcNAc-P-P-Dol ; GDP-Man, guanosyl diphosphomannose ; Dol-P-Man, mannosylphosphoryldolichol ; OS-GlcNAc 2 , soluble oligosaccharides possessing a diN -acetylchitobiose sequence at their reducing end ; OS-GlcNAc 1 , soluble oligosaccharides possessing a single Nacetylglucosamine residue at their reducing end ; PNGase F, peptide N-glycosidase F (EC 3.5.1.52) ; Endo H, endo-N-acetyl-β-D-glucosaminidase H (EC 3.2.1.96).