Evidence That Oxidized Proteins are Substrates for N-Terminal Arginylation

While the posttranslational N-terminal arginylation of proteins has been demonstrated in a variety of eukaryotic cells including neurons and their axons, the targets of the reaction are poorly understood. Several lines of evidence suggest that arginylation may be a cytoprotective mechanism used by cells to target oxidatively damaged (and thus potentially toxic) proteins for degradation. In the present experiments, we have begun to test this hypothesis by incubating oxidized test proteins in a rat brain extract capable of arginylating endogenous proteins. Bovine serum albumin, pancreatic ribonuclease-A and the A-chain of insulin were chosen as test proteins and either oxidized by metal catalyzed oxidation or purchased in their oxidized forms and incubated with the extract and ³H]Arg. SDS PAGE of the incubation product showed ³H]Arg migrating with the oxidized forms of BSA and RNase but not with the un-oxidized form of BSA. Following incubation with the oxidized A-chain of insulin, analysis of the ³H]product by SDS PAGE and HPLC showed co-migration of ³H]Arg with A-chain standards and amino acid sequencing showed ³H]Arg at the N-terminus of the A-chain of insulin. The data suggest that oxidative damage to a protein may be a signal for its N-terminal arginylation.