TRIM52 Ubiquitin Ligase Acts as a Key Recognition Component of the Mammalian fMet/N-degron Pathway

Eukaryotic translation can initiate with formylmethionine (fMet), generating N-terminally formylated proteins in mitochondria and, unexpectedly, in the cytosol. However, the specific mechanism for eliminating cytosolic fMet-bearing proteins has remained elusive. Here, we identify the E3 ubiquitin ligase TRIM52 as the key recognition component of the mammalian fMet/N-degron pathway. TRIM52 targets N-terminally formylated proteins, including TPD54 and SPTAN1, for proteasomal degradation. It recognizes the N-terminal fMet through an evolutionarily conserved acidic loop embedded between its bipartite RING domain. Structural modeling and mutagenesis identify Tyr148 in the acidic loop as critical for fMet recognition without intervening E3 ligase activity. TRIM52 depletion stabilizes fMet-bearing proteins, disrupts proteostasis, and induces caspase-3-dependent apoptosis—phenotypes rescued by enhancing deformylation. These findings establish TRIM52 as a dedicated sensor and effector of the mammalian fMet/N-degron pathway, linking N-terminal formylation to proteostasis and cell survival.