N-linked glycosylation of beta-amyloid precursor protein.

The beta-amyloid peptide that accumulates in the brain of patients with Alzheimer's disease is derived by proteolytic processing of a family of membrane bound beta-amyloid precursor proteins (beta APPs). The three major isoforms of beta APP, 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 beta-amyloid deposition in brain are not clear. It is possible that defects in metabolic and processing pathways of beta APP lead to the increased production and deposition of beta-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 beta APP 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 beta APP 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 beta APP.