PTS2

PTS2, or peroxisomal targeting signal type 2, is a short amino acid sequence that directs a protein to peroxisomes. It is usually located at the N terminus of the cargo protein and serves as an alternative to the more common PTS1 signal at the C terminus. The PTS2 signal is a short nonapeptide, though many functional signals deviate from a strict consensus. It often features a conserved arginine near the start of the motif and a leucine closer to the end, but there is substantial variability across proteins and species.

Recognition of PTS2-containing cargo is mediated by the cytosolic receptor Pex7, which binds the signal and facilitates delivery to the peroxisomal membrane. Import typically involves interaction with a docking complex, commonly including peroxins such as Pex13 and Pex14, and requires additional factors to translocate the cargo into the peroxisomal matrix. After delivery, the receptor is recycled to the cytosol through ubiquitination and other recycling steps, enabling multiple rounds of import.

PTS2-bearing proteins include several peroxisomal enzymes involved in lipid metabolism, such as certain thiolases and other beta-oxidation components. In many organisms, some proteins can be targeted by both PTS2 and PTS1 signals, providing redundancy or tissue- and development-specific targeting options.

Defects in PTS2 signaling or in Pex7 function can impair peroxisomal import, contributing to peroxisomal biogenesis disorders in humans and other organisms. Research continues to refine the understanding of PTS2 consensus elements, cargo scope, and species-specific variations in the import machinery.

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