Ribosomally synthesized and post-translationally modified peptides (RiPPs) are a family of natural products that present a common biosynthetic pathway. These natural products begin as precursor peptides directly produced from ribosomes and undergo a series of post-translational modifications. The precursor peptides all consist of a leader peptide region, which is important for recognition by biosynthetic enzymes, and a core peptide region, which is modified to form the final natural product. In our lab, we are focusing on the elucidation of the biosynthesis of Microviridin J, a serine protease inhibitor produced by the freshwater cyanobacteria, Microcystis aeruginosa. Our goal is to use protein crystallography to understand the mechanism of how the precursor peptide is modified by the biosynthetic enzymes in the pathway. This understanding will lead to protein engineering approaches to create analogs of microviridin that can be used for therapeutic purposes.