PEX5n

PEX5n is the N-terminal portion of the peroxisomal import receptor PEX5 in organisms where the PEX5 gene is split into two separate polypeptides, PEX5N and PEX5C. In these lineages, the receptor's function is carried by a heteromeric complex formed by PEX5N and PEX5C rather than a single polypeptide chain. PEX5n provides the N-terminal docking and regulatory regions, while PEX5C contains the C-terminal tetratricopeptide repeats that bind the peroxisomal targeting signal 1 (PTS1) on cargo proteins.

Structurally, PEX5n lacks the full cargo-binding domain found in canonical PEX5 but carries interaction surfaces and motifs that coordinate docking at the peroxisomal membrane. It contributes to the receptor assembly by engaging with the peroxisomal membrane docking complex, including proteins such as PEX13 and PEX14, and with the ubiquitination and recycling machinery that regulate receptor turnover. Although it does not bind PTS1 directly, PEX5n works in concert with PEX5C to form a functional import receptor.

Functionally, the PEX5N–PEX5C complex mediates the import of matrix proteins into peroxisomes. PTS1-bearing cargo binds via the PEX5C TPR domain, while PEX5N participates in docking, proper receptor localization, and recycling. The two subunits must associate to enable efficient cargo recognition and translocation across the peroxisomal membrane.

Occurrence and evolution: Split PEX5 systems, featuring PEX5N and PEX5C, have been observed in certain plants, algae, and protists. This architecture represents an evolutionary variation of the conserved PEX5 pathway, with functional conservation maintained through heteromeric receptor operation rather than a single polypeptide chain.