Pex17p is required for import of both peroxisome membrane and lumenal protein and interacts with Pex19p and the peroxisome targeting signal-receptor docking complex in Pichia pastoris

Pichia pastoris PEX17 was cloned by complementation of:a peroxisome-deficie nt strain obtained from a novel screen for mutants disrupted in the localiz ation of a peroxisomal membrane protein (PMP) reporter. PEX17 encodes a 267 -amino-acid protein with low identity (18%) to the previously characterized Saccharomyces cerevisiae Pex17p.,Like ScPex17p, PpPex17p contains a putati ve transmembrane domain near the amino terminus and two carboxyl-terminal c oiled-coil regions. PpPex17p behaves as an integral PMP with a cytosolic ca rboxyl-terminal domain. pex17 Delta mutants accumulate peroxisomal matrix p roteins and certain integral PMPs in the cytosol, suggesting a critical rol e for Pex17p in their localization. Peroxisome remnants were observed in th e pex17 Delta mutant by morphological and biochemical means, suggesting tha t Pex17p is not absolutely required for remnant formation. Yeast two-hybrid analysis demonstrated that the carboxyl terminus of Pex19p was required fo r interaction with Pex17p lacking the carboxyl-terminal coiled-coil domains . Biochemical evidence confirmed the interaction between Pex19p and Pex17p. Additionally, Pex17p cross-linked to components of-the peroxisome targetin g signal-receptor docking complex, which unexpectedly contained Pex3p. Our evidence suggests the existence of distinct subcomplexes that contain separ able pools of:Pex3p, Pex19p, Pex17p, Pex14p, and the peroxisome targeting s ignal receptors. These distinct pools may serve different purposes for the import of matrix proteins or PMPs.