A protein A that binds to the N-methyl-D-aspartate (NMDA) receptor and a protein B that interacts with protein A are provided. Furthermore, based on the marked promotion of the NMDA receptor mediated signal transduction by these proteins, providing a controlling agent (an inhibiting agent or a promoting agent) and a controlling method for the expression and/or the function of these proteins makes possible the elucidation of diseases caused by an anomaly in the NMDA receptor mediated signal transduction or in memory recall, including such neurodegenerative diseases as Alzheimer's disease, Parkinson's disease and polyglutamine disease, and allows for the prevention, improvement or treatment thereof.