Manipulating Cation-π Interactions of Reader Proteins in Living Cells with Genetic Code Expansion.

Despite tremendous success in understanding the chemical nature and the importance of cation-π interactions in a range of biological processes, particularly in epigenetic regulation, the design and synthesis of stronger cation-π interactions in living cells remain largely elusive. Here, we design several electron-rich Trp derivatives and incorporate them into histone methylation reader domains to enhance the affinity of the reader domains for histone methylation marks via cation-π interactions in living cells. We show that this site-specific Trp replacement strategy is generally applicable for the engineering of high-affinity reader domains for the major histone H3 trimethylation marks, such as H3K4me3, H3K9me3, H3K27me3, and H3K36me3, with high specificity. Furthermore, we demonstrate that engineered reader domains can serve as powerful tools for the enrichment and imaging of histone methylation, as well as for capturing the protein interactome at chromatin marks in living cells. Therefore, our study paves the way for the design of enhanced cation-π interactions in reader proteins in living cells for various biological applications.