(CG)-SLENP: A Chemical Genetics Strategy To Selectively Label Existing Proteins and Newly Synthesized Proteins.

Protein synthesis and subsequent delivery to the target locations in cells are essential for their proper functions. Methods to label and distinguish newly synthesized proteins from existing ones are critical to assess their differential properties, but such methods are lacking. We describe the first chemical genetics-based approach for selective labeling of existing and newly synthesized proteins that we termed as (CG)-SLENP. Using HaloTag in-frame fusion with lamin A (LA), we demonstrate that the two pools of proteins can be selectively labeled using (CG)-SLENP in living cells. We further employ our recently developed selective small molecule ligand LBL1 for LA to probe the potential differences between newly synthesized and existing LA. Our results show that LBL1 can differentially modulate these two pools of LA. These results indicate that the assembly states of newly synthesized LA are distinct from existing LA in living cells. The (CG)-SLENP method is potentially generalizable to study any cellular proteins.