The structure of an Amyloid Precursor Protein/talin complex indicates a mechanical basis of Alzheimer's Disease.

Abstract

Misprocessing of Amyloid Precursor Protein (APP) is one of the major causes of Alzheimers disease. APP is a transmembrane protein comprising a large extracellular region, a single transmembrane helix and a short cytoplasmic tail containing an NPxY motif (normally referred to as the YENPTY motif). Talins are synaptic scaffold proteins that connect the cytoskeletal machinery to the plasma membrane via binding to one of two highly conserved NPxY motifs in the cytoplasmic tail of integrin transmembrane receptors. Here we report the crystal structure of an APP/talin1 complex identifying a new way to couple the cytoskeletal machinery to synaptic sites via APP. Proximity Ligation Assay (PLA) confirmed the close proximity of talin1 and APP in primary neurons, and we show that talin1 depletion has a dramatic effect on APP processing in cells. Structural modelling indicates that APP has the capacity to form an extracellular meshwork that mechanically couples the cytoskeletal meshworks of both the pre-, and post-synaptic compartments. In this context, we propose APP processing as a mechanical signalling pathway with similarities to Notch signalling, whereby the cleavage sites in APP represent mechanical sensors, with varying accessibility to cleavage by secretases. During synaptogenesis in healthy neurons, the APP/talin linkage would provide an exquisite mechanical coupling between synapses, with tightly controlled APP processing providing instructions to maintain this synchrony. Furthermore, APP directly coupling to the binary switches in talin indicates a role for APP in mechanical memory storage as postulated by the MeshCODE theory. The implication that APP is a regulator of mechanical signalling leads to a new hypothesis for Alzheimers disease, where mis-regulation of APP dynamics results in loss of mechanical integrity of the synapse, corruption and loss of mechanical binary data, and excessive generation of the toxic plaque-forming A{beta}42 peptide. Much needs to be done to experimentally validate this idea, but we present here a novel theory of Alzheimers Disease with a role for APP in the mechanically coded binary information storage in the synapse, which identifies a potential novel therapeutic strategy for treating Alzheimers Disease. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=131 SRC="FIGDIR/small/583202v4_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@ba0768org.highwire.dtl.DTLVardef@13c4672org.highwire.dtl.DTLVardef@352178org.highwire.dtl.DTLVardef@288bf6_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical AbstractC_FLOATNO Graphical Abstract Legend: Amyloid Precursor Protein (APP) forms an extracellular meshwork that provides a coupling between the mechanical signalling machinery of the pre- and post-synaptic neurons.A) APP binds to talin indicating that APP will experience mechanical forces which leads us to propose that APP processing is a Notch-like signalling pathway that maintains mechanical homeostasis at the synapse. B) The crystal structure of APP bound to talin F2F3. C) APP is part of the adhesion complex that attaches talin to the membrane. D) The loss of adhesion integrity in the synapse, or other factors that lead to misprocessing of APP will perturb this coupling and contribute to Alzheimers Disease. See also Movie 1. C_FIG