The Amyloid Precursor Protein Shows a pH-Dependent Conformational Switch in Its E1 Domain

Abstract

The amyloid precursor protein (APP) and its proteolytic cleavage product Aβ are widely believed to be central to the etiology of Alzheimer's disease (AD). APP and its family members are also essential for proper neuronal development and homeostasis. APP is located at the cell surface and within intracellular compartments, cellular regions that exhibit different pH values. The AD-associated amyloidogenic processing of APP is initiated predominantly in intracellular acidic compartments, whereas its non-amyloidogenic cleavage is initiated at the cell surface at slightly basic pH. We analyzed the influence of pH on the APP-E1 domain and found that its two constituting subdomains, GFLD and CuBD, interact with each other in a pH-dependent manner. Dynamic light scattering showed that APP-E1 represents a more open conformation at neutral pH and a more closed conformation at acidic pH. Analyzing a 1.4 Å, high-resolution X-ray structure of E1 derived from merohedrally twinned crystals resulted in the identification of individual residues that are responsible for these pH-dependent interactions. Mutational studies and dynamic light scattering measurements further proved that specific hydrogen bonds between the two carboxylates of D177 and E87, as well as between N89 and H147, are major determinants of this pH-driven conformational switch in APP-E1. These findings show how APP can adopt different conformations depending on pH and suggest that the protein fulfils different functions at distinct localizations within the cell. Additionally, our data suggest a novel strategy for treating AD based on regulating the amyloidogenic processing of APP by the specific interruption of the interaction between the APP-E1 subdomains.

APP Receptor? To Be or Not To Be

“…A pH-dependent interaction between the GFLD subdomain interaction with the copper binding domain (CuBD) within the E1 domain will allow APP to adopt a closed conformation in more acidic compartment, whereas it will adopt a more opened conformation at neutral pH. Consequently, APP at the cell surface (pH ~7.4) – in its open conformation - would be poised to expose the E1 domain and favor association with other proteins or putative ligands, which is consistent with noticeable higher molecular weight complex formation and its dimerization pattern [95] (see Figure 4b). Thus, the pH-dependent molecular conformation switch may provide APP the ability to fulfill different physiological functions in different cellular localizations.…”

“…The APP ectodomain has also the property to adopt different conformations depending on the cellular pH [95] . A pH-dependent interaction between the GFLD subdomain interaction with the copper binding domain (CuBD) within the E1 domain will allow APP to adopt a closed conformation in more acidic compartment, whereas it will adopt a more opened conformation at neutral pH.…”

Investigation of the molecular similarity in closely related protein systems: The PrP case study

“…The identification of structural features connected to the amyloid propensity of certain mutants may also lead to a better elucidation of the mechanism of action of other proamyloidogenic stimuli. In this case, it can be hypothesized that either physical or chemical stimuli may act on the normally folding isoform by inducing the same structural features identified in its pathogenic mutants, as paved by several experimental and computational evidences . In this article, we present a computational protocol based on the combination of molecular dynamics (MD) and grid‐based approaches for the investigation of the molecular interaction properties of closely related protein systems.…”

Amyloids: from pathogenesis to function

“…Different pH dependent conformational rearrange ments of the amyloid β peptide precursor protein can also exist [132,133]. Whether such ambiguity is associat ed only with the initiation stage or also with the elonga tion stage of TP II is now under study on the prion [PSI + ] model [134].…”