The Functions of the Amyloid Precursor Protein Gene and Its Derivative Peptides: I Molecular Biology and Metabolic Processing

The amyloid precursor protein gene (APP) and its derivative peptides have important functions in the central nervous system. APP and Aβ fulfil criteria as neuractive peptides: presence, release and identity of action. Aβ is a peptide of 1 - 43 amino acids in length, derived from APP and the major component of the core of neuritic plaques found in Alzheimer’s disease. Analysis of the cDNA of Aβ revealed its origins from the larger precursor protein. There are at least four types of mRNA generated by alternative splicing of exons 7 and 8. Exon 7 encodes a 57 amino acid sequence found in the extracellular domain with major homology to the Kunitz-type of serine protease inhibitors. APP is cleaved by three secretases known as α, β, and γ secretase which act on APP at different sites producing various fragments of differing amino acid length. The γ secretase is a macromolecular enzyme complex composed of presenilin 1, 2 and other molecular constitutents essential for its function.