PEX12 interacts with PEX5 and PEX10 and acts downstream of receptor docking in peroxisomal matrix protein import

Peroxisomal matrix protein import requires PEX12, an integral peroxisomal m embrane protein with a zinc ring domain at its carboxy terminus. Mutations in human PEX12 result in Zellweger syndrome, a lethal neurological disorder , and implicate the zinc ring domain in PEX12 function. Using two-hybrid st udies, blot overlay assays, and coimmunoprecipitation experiments, we obser ved that the zinc-binding domain of PEX12 binds both PEX5, the PTS1 recepto r, and PEX10, another integral peroxisomal membrane protein required for pe roxisomal matrix protein import. Furthermore, we identified a patient with a missense mutation in the PEX12 zinc-binding domain, S320F, and observed t hat this mutation reduces the binding of PEX12 to PEX5 and PEX10. Overexpre ssion of either PEX5 or PEX10 can suppress this PEX12 mutation, providing g enetic evidence that these interactions are biologically relevant. PEX5 is a predominantly cytoplasmic protein and previous PEX5-binding proteins have been implicated in docking PEX5 to the peroxisome surface. However, we fin d that loss of PEX12 or PEX10 does not reduce the association of PEX5 with peroxisomes, demonstrating that these peroxins are not required for recepto r docking. These and other results lead us to propose that PEX12 and PEX10 play direct roles in peroxisomal matrix protein import downstream of the re ceptor docking event.