Neurodegeneration correlates with Alzheimer's disease (AD) symptoms, but the molecular identities of pathogenic amyloid beta-protein (A beta) oligomers and their targets, leading to neurodegeneration, remain unclear. Amylospheroids (ASPD) are AD patient-derived 10- to 15-nm spherical A beta oligomers that cause selective degeneration of mature neurons. Here, we show that the ASPD target is neuronspecific Na+/K+-ATPase alpha 3 subunit (NAK alpha 3). ASPD-binding to NAK alpha 3 impaired NAK alpha 3-specific activity, activated N-type voltage-gated calcium channels, and caused mitochondrial calcium dyshomeostasis, tau abnormalities, and neurodegeneration. NMR and molecular modeling studies suggested that spherical ASPD contain N-terminal-A beta-derived "thorns" responsible for target binding, which are distinct from low molecular-weight oligomers and dodecamers. The fourth extracellular loop (Ex4) region of NAK alpha 3 encompassing Asn(879) and Trp(880) is essential for ASPD-NAK alpha 3 interaction, because tetrapeptides mimicking this Ex4 region bound to the ASPD surface and blocked ASPD neurotoxicity. Our findings open up new possibilities for knowledge-based design of peptidomimetics that inhibit neurodegeneration in AD by blocking aberrant ASPD-NAK alpha 3 interaction.