Neuropeptides and peptide hormones are cell-to-cell signaling molecules that facilitate communication between cells within the central nervous and endocrine systems, and dysregulation of these signaling events often leads to disease. Characterizing the active forms and molecular-level interactions of cell-cell signaling peptides represents a significant goal to understand how living systems carry out complex tasks (e.g., responding to stress, regulating bodily functions, learning), and may identify novel therapeutic targets.