title: Solution conformation and heparin-induced dimerization of the full-length extracellular domain of the human amyloid precursor protein.
abstract: Proteolytic cleavage of the amyloid precursor protein (APP) by beta and gamma-secretases gives rise to the beta-amyloid peptide, considered to be a causal factor in Alzheimer's disease. Conversely, the soluble extracellular domain of APP (sAPPalpha), released upon its cleavage by alpha-secretase, plays a number of important physiological functions. Several APP fragments have been structurally characterized at atomic resolution, but the structures of intact APP and of full-length sAPPalpha have not been determined. Here, ab initio reconstruction of molecular models from high-resolution solution X-ray scattering (SAXS) data for the two main isoforms of sAPPalpha (sAPPalpha(695) and sAPPalpha(770)) provided models of sufficiently high resolution to identify distinct structural domains of APP. The fragments for which structures are known at atomic resolution were fitted within the solution models of full-length sAPPalpha, allowing localization of important functional sites (i.e. glycosylation, protease inhibitory and heparin-binding sites). Furthermore, combined results from SAXS, analytical ultracentrifugation (AUC) and size-exclusion chromatography (SEC) analysis indicate that both sAPPalpha isoforms are monomeric in solution. On the other hand, SEC, bis-ANS fluorescence, AUC and SAXS measurements showed that sAPPalpha forms a 2:1 complex with heparin. A conformational model for the sAPPalpha:heparin complex was also derived from the SAXS data. Possible implications of such complex formation for the physiological dimerization of APP and biological signaling are discussed in terms of the structural models proposed.
authors.affiliation: Instituto de Bioquímica Médica, Programa de Bioquímica e Biofísica Celular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21944-590, Brazil.
authors.forename: Matthias
authors.initials: M
authors.lastname: Gralle
authors.forename: Cristiano L P
authors.initials: CL
authors.lastname: Oliveira
authors.forename: Luiz H
authors.initials: LH
authors.lastname: Guerreiro
authors.forename: William J
authors.initials: WJ
authors.lastname: McKinstry
authors.forename: Denise
authors.initials: D
authors.lastname: Galatis
authors.forename: Colin L
authors.initials: CL
authors.lastname: Masters
authors.forename: Roberto
authors.initials: R
authors.lastname: Cappai
authors.forename: Michael W
authors.initials: MW
authors.lastname: Parker
authors.forename: Carlos H I
authors.initials: CH
authors.lastname: Ramos
authors.forename: Iris
authors.initials: I
authors.lastname: Torriani
authors.forename: Sérgio T
authors.initials: ST
authors.lastname: Ferreira
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry; D019281:Dimerization; D006493:Heparin / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D014461:Ultracentrifugation
chemical_list: D016564:Amyloid beta-Protein Precursor; D020033:Protein Isoforms; D006493:Heparin