Our research project proposes to use protein crystallography to structurally characterize the four enzymes involved in the biosynthesis of microviridins, a subset of ribosomally synthesized and post-translationally modified peptides (RiPPs). The precursor peptides of RiPPs consist of a leader peptide (LP) region important for enzyme recognition and a core peptide region (CP) that is modified by these enzymes to form the mature product. The RiPPs family of natural products presents a diversity of molecules with therapeutic potential, exemplified by the resistance to proteolytic degradation and serine protease inhibition of microviridins. This project aims to study the biosynthesis of microviridin J, which is produced by the cyanobacteria Microcystis aeruginosa. We will also study a homologous pathway in the cyanobacteria Anabaena sp. PCC 7120, which contains a unique precursor peptide encoding for three putative CPs. The isolation of microviridin J through heterologous expression in E. coli is another strategy we will use for understanding RiPPs biosynthetic logic. We aim to reprogram microviridin biosynthetic machinery to create bioactive cyclic peptides using the cage-like architecture of microviridins as a scaffold for synthetic biology.