N-linked glycosylation of β-amyloid precursor protein

The β-amyloid peptide that accumulates in the brain of patients with Alzheimer's disease is derived by proteolytic processing of a family of membrane bound β-amyloid precursor proteins (βAPPs). The three major isoforms of βAPP, derived by alternative splicing, contain 695, 751, and 770 amino acids. They are heavily O-glycosylated and contain two N-linked glycosylation sites. The pathways leading to β-amyloid deposition in brain are not clear. It is possible that defects in metabolic and processing pathways of βAPP lead to the increased production and deposition of β-amyloid. In many cases post-translational modifications, such as glycosylation, are important in regulating such pathways. We studied N-linked glycosylation of the 695 amino acid form of βAPP in detail by deleting the two potential glycosylation sites at Asn₄₆₇ and Asn₄₉₆. The mutants were examined both in a cell-free transcription/translation/glycosylation system and in transfected Chinese hamster ovary (CHO) cells. In both systems, only Asn₄₆₇ was glycosylated. In CHO cells the N-linked oligosaccharide on βAPP was completely resistant to Endoglycosidase H, suggesting that it is of complex type. These mutants will be useful for studying the role of glycosylation in the metabolism of βAPP.