Here, we demonstrate that Tysnd1, a previously uncharacterized protein, is responsible both for the removal of the leader peptide from PTS2 proteins and for the specific processing of PTS1 proteins. All of the identified Tysnd1 substrates catalyze peroxisomal β-oxidation. In vitro cleavage of Acox1, Scp2 and prethiolase by recombinant Tysnd1.