Prion protein (PrP) contains two N-linked glycosylation sites. It is unknown which amino acid substitution contributes most efficiently to the abolishment of N-linked glycosylations. To define the influence of amino acid substitution at the N-linked glycosylation sites on the conversion efficiency of mouse PrP, we tested each of all 19 amino acid substitutions at either one of the Winked glycosylation sites (codon 180, 182, 196 or 198). The conversion efficiency of the mutagenized PrP was highly dependent on the newly introduced amino acid itself regardless of the absence of Winked glycosylation in scrapie-infected mouse neuroblastoma cells. The majority of mutant PrP with substitutions at the Asn residues of the Winked glycosylation sites were conversion-competent, whereas most mutant PrP with substitutions at the Thr residues were conversion-incompetent. These findings emphasize that the Asn residues of the N-linked glycosylation sites are replaceable to abolish Winked glycosylations without directly affecting the protein function. (C) 2008 Elsevier Inc. All rights reserved.