Abstract
Modification at specific sites has long been a central goal in peptide and protein chemistry. Introducing functional groups at specific sites is an ideal state for protein function research and the modification of protein properties, as it can eliminate the interference caused by heterogeneous modifications. Recent downstream applications have placed even greater demands on site selectivity. This review examines the latest advances in the site-specific modification of peptides and proteins, organizing the reactions into four categories: exploiting disparities in chemical environments, tag-and-modify approaches, proximity-driven chemical modification, and enzymatic strategies. For each reaction, we detail the underlying design rationale and highlight downstream chemical and biological applications. Collectively, these methods have achieved remarkable gains in terms of specificity, efficiency, and scope, furnishing a versatile chemical toolbox for the site-selective functionalization of peptides and proteins. We conclude by summarizing the current state of the field and outlining prospective directions for future development.