Methods for elucidating biopolymer interactions with known and/or unknown small molecules (e.g. candidate drug compounds) are disclosed. These methods utilize novel (usually motile) organisms transformed with one or more heterologous biopolymer sequences. Biopolymer expression is promoted in cells mediating movement in said organism, generally dually-promoted in paired sets of cells mediating oppositely-directed movement. Modulation of motility in the resultant organism due to the presence of small molecules demonstrates small molecule interaction with said natural and/or mutated biopolymer. Analyzed in a chemical gradient, one or more interacting small molecule species can be identified by oriented migration, even in the presence of one or more non-interacting small molecule species. A competing and/or interfering biopolymer can be introduced without obscuring the motility signal. Methods described herein have utility for the discovery of novel therapeutic compounds (drug discovery), for the improvement of existing therapeutic compounds (drug refinement), and for the precise identification of small molecule binding sites on biopolymers via mutagenesis (structural elucidation). A specific embodiment, a Nematode Olfaction-based Structural Elucidation (NOSE) assay, is described herein.