Ribosomally synthesized and post-translationally modified peptides (RiPPs) are an important source of bioactive natural products. The cross-links between aromatic amino acid side chains (cyclophane cross-links) confer structural diversity and complexity. These cross-links are primarily catalyzed by two major types of enzymes: radical S-adenosylmethionine (rSAM) enzymes and cytochrome P450 enzymes. This review focuses on the diverse cyclophane cross-linking patterns introduced by rSAM and P450 enzymes during RiPP biosynthesis, and summarizes the similarities and differences between these enzymatic transformations, aiming to provide some insights for the discovery, engineering, and mechanistic study of this class of natural products.

Cytochrome P450 enzymes represent a class of heme-containing protease widely distributed across the biological kingdom. Endowed with a broad substrate scope, diverse catalytic reaction profiles, high regio- and stereoselectivity toward substrates, and mild catalytic conditions, these enzymes stand out as superior biocatalysts with good potential of application. As one of the primary producers of natural products, Streptomyces harbors a wealth of P450 enzymes and natural product biosynthetic gene clusters (BGCs) in its genome, making it a versatile treasure trove for the generation of bioactive small-molecule compounds. This review summarizes the catalytic reactions by Streptomyces-derived P450 enzymes in natural product biosynthesis and delineates the engineering strategies for addressing the practical application challenges of P450 enzymes, aiming to provide some reference and guidance for in-depth research on P450 enzymes and their applications.