Functions as an intracellular leucine sensor that negatively regulates the TORC1 signaling pathway through the GATOR complex. In absence of leucine, binds the GATOR subcomplex GATOR2 and prevents TORC1 signaling. Binding of leucine to SESN2 disrupts its interaction with GATOR2 thereby activating the TORC1 signaling pathway. This stress-inducible metabolic regulator also plays a role in protection against oxidative and genotoxic stresses. May negatively regulate protein translation in response to endoplasmic reticulum stress, via TORC1. May positively regulate the transcription by NFE2L2 of genes involved in the response to oxidative stress by facilitating the SQSTM1-mediated autophagic degradation of KEAP1. May also mediate TP53 inhibition of TORC1 signaling upon genotoxic stress. Moreover, may prevent the accumulation of reactive oxygen species (ROS) through the alkylhydroperoxide reductase activity born by the N-terminal domain of the protein. Was originally reported to contribute to oxidative stress resistance by reducing PRDX1. However, this could not be confirmed. a hydroperoxide + L-cysteinyl-[protein] = an alcohol + S-hydroxy-L-cysteinyl-[protein] Interacts with the GATOR2 complex which is composed of MIOS, SEC13, SEH1L, WDR24 and WDR59; the interaction is negatively regulated by leucine. Interacts with RRAGA, RRAGB, RRAGC and RRAGD; may function as a guanine nucleotide dissociation inhibitor for RRAGs and regulate them. May interact with the TORC2 complex. Interacts with KEAP1, RBX1, SQSTM and ULK1; to regulate the degradation of KEAP1. May also associate with the complex composed of TSC1, TSC2 and the AMP-responsive protein kinase/AMPK to regulate TORC1 signaling. May interact with PRDX1. The N-terminal domain has an alkylhydroperoxide reductase activity. The C-terminal domain mediates interaction with GATOR2 through which it regulates TORC1 signaling. Phosphorylated by ULK1 at multiple sites. Ubiquitinated at Lys-166 by RNF167 via 'Lys-63'-linked polyubiquitination in response to leucine deprivation: ubiquitination promotes SESN2-interaction with the GATOR2 complex, leading to inhibit the TORC1 signaling pathway. Deubiquitinated at Lys-166 by STAMBPL1, promoting the TORC1 signaling pathway. Ubiquitinated by RNF186; ubiquitination mediates proteasomal degradation. Belongs to the sestrin family.