Glycosylation differences between the normal and pathogenic prion protein isoforms

Glycosylation differences between the normal and pathogenic prion protein isoforms

^*Glycobiology Institute, Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, United Kingdom; ^‡Institute for Neurodegenerative Diseases, Departments of Neurology and Biochemistry and Biophysics, HSE-781, University of California, San Francisco, CA 94143-0518; and ^†Tokyo Metropolitan Institute of Gerontology, 35-2 Sakaecho Itabashi-ku, Tokyo 173, Japan

Contributed by Stanley B. Prusiner

Abstract

Prion protein consists of an ensemble of glycosylated variants or glycoforms. The enzymes that direct oligosaccharide processing, and hence control the glycan profile for any given glycoprotein, are often exquisitely sensitive to other events taking place within the cell in which the glycoprotein is expressed. Alterations in the populations of sugars attached to proteins can reflect changes caused, for example, by developmental processes or by disease. Here we report that normal (PrP^C) and pathogenic (PrP^Sc) prion proteins (PrP) from Syrian hamsters contain the same set of at least 52 bi-, tri-, and tetraantennary N-linked oligosaccharides, although the relative proportions of individual glycans differ. This conservation of structure suggests that the conversion of PrP^C into PrP^Sc is not confined to a subset of PrPs that contain specific sugars. Compared with PrP^C, PrP^Sc contains decreased levels of glycans with bisecting GlcNAc residues and increased levels of tri- and tetraantennary sugars. This change is consistent with a decrease in the activity of N-acetylglucosaminyltransferase III (GnTIII) toward PrP^C in cells where PrP^Sc is formed and argues that, in at least some cells forming PrP^Sc, the glycosylation machinery has been perturbed. The reduction in GnTIII activity is intriguing both with respect to the pathogenesis of the prion disease and the replication pathway for prions.

N-acetylglucosaminyltransferase III scrapie

Footnotes

↵ § To whom reprint requests should be addressed.
Abbreviations:

PrP,

prion protein;

PrPC,

normal PrP;

PrPSc,

disease-causing conformer PrP;

SHa,

Syrian hamster;

GNTIII,

N-acetylglucosaminyltransferase III;

A(1–4),

the number of GlcNAc antennae linked to the trimannosyl core;

G(0–4),

the number of Gal residues in the structure;

F(1–4),

the number of Fuc residues in the structure;

H,

hexose (Man, Gal);

N,

N-acetyl hexosamine;

B,

bisecting GlcNAc;

S,

sialic acid;

MALDI-TOF MS,

matrix-assisted laser desorption ionization-time of flight MS;

2-AB,

2-aminobenzamide