May function 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 may also play a role in protection against oxidative and genotoxic stresses. May prevent the accumulation of reactive oxygen species (ROS) through the alkylhydroperoxide reductase activity born by the N-terminal domain of the protein. a hydroperoxide + L-cysteinyl-[protein] = an alcohol + S-hydroxy-L-cysteinyl-[protein] At zygotic stage; specifically expressed in the notochord. Maternal transcripts are detected at cleavage stages and reduced during gastrulation. The N-terminal domain may have an alkylhydroperoxide reductase activity. The C-terminal domain mediates interaction with GATOR2 through which it regulates TORC1 signaling. Belongs to the sestrin family.