Provided herein are nucleic acids encoding human NMDA receptor protein subunits and the proteins encoded thereby. In one aspect of the invention, the nucleic acids encode provides In a preferred embodiment, the invention nucleic acids encode MNDAR1, NMDAR2A, NMDAR2B, NMDAR2C and NMDAR2D subunits of human NMDA receptors. The disclosed nucleic acids are also useful as probes, thus enabling those skilled in the art, to identify and isolate related human receptor subunits. Functional glutamate receptors can be assembled, in accordance with the present invention, from a plurality of one type of NMDA receptor subunit protein (homomeric) or from a mixture of two or more types of subunit proteins (heteromeric). Also provided are methods for using the disclosed receptor subunits to identify and characterize compounds which affect the function of such receptors, e.g., agonists, antagonists, and modulators of glutamate receptor function. Methods for determining whether unknown protein(s) are functional as NMDA receptor subunits are also provided.