Arginyltransferase ATE1 Catalyzes Midchain Arginylation of Proteins at Side Chain Carboxylates In Vivo

•Multiple proteins are arginylated in vivo on side chains of Asp and Glu•ATE1 can mediate both N-terminal and midchain arginylation of Asp and Glu•Both amino and carboxyl group of the N-terminal Asp facilitate arginylation•ATE1 adds Arg predominantly to protein side chains rather than the N terminus

SummaryArginylation is an emerging posttranslational modification mediated by Arg-tRNA-protein-transferase (ATE1). It is believed that ATE1 links Arg solely to the N terminus of proteins, requiring prior proteolysis or action by Met-aminopeptidases to expose the arginylated site. Here, we tested the possibility of Arg linkage to midchain sites within intact protein targets and found that many proteins in vivo are modified on the side chains of Asp and Glu by unconventional chemistry that targets the carboxy rather than the amino groups at the target sites. Such arginylation appears to be functionally regulated, and it can be directly mediated by ATE1, in addition to the more conventional ATE1-mediated linkage of Arg to the N-terminal alpha amino group. This midchain arginylation implies an unconventional mechanism of ATE1 action that likely facilitates its major biological role.