Numerous small molecules serve to coordinate many biological activities within cells of multicelluar organisms. These ligand-receptor interactions are vital to the control of cellular processes such as altering cellular membrane potential and activation of gene transcription. This dissertation includes two ligand-receptor interactions projects: validating a small molecule as a selective photoreactive antagonist, ANQX, for AMPA receptors at synapses using x-ray crystallography and mass spectroscopy; and, utilizing a directed evolution yeast based selection assay to re-engineer the androgen receptor to activate transcription with gestrinone, a proof-of-concept drug. These two projects combined provide additional insight into the molecular basis of ligand-receptor interactions of ion channels and steroid nuclear receptors.