Overproduction of Pex5p stimulates import of alcohol oxidase and dihydroxyacetone synthase in a Hansenula polymorpha pex14 null mutant

Hansenula polymorpha Delta pex14 cells are affected in peroxisomal matrix p rotein import and lack normal peroxisomes. Instead, they contain peroxisoma l membrane remnants, which harbor a very small amount of the major peroxiso mal matrix enzymes alcohol oxidase (AO) and dihydroxyacetone synthase (DHAS ). The bulk of these proteins is, however, mislocated in the cytosol, Here, we show that in Delta pex14 cells overproduction of the PTS1 receptor, Pex 5p, leads to enhanced import of the PTS1 proteins AO and DHAS but not of th e PTS2 protein amine oxidase. The import of the PTS1 protein catalase (CAT) was not stimulated by Pex5p overproduction. The difference in import behav ior of AO and CAT was not related to their PTS1, since green fluorescent pr otein fused to the PTS1 of either AO or CAT were both not imported in Delta pex14 cells overproducing Pex5p. When produced in a wild type control stra in, both proteins were normally imported into peroxisomes. In Delta pex14 c ells overproducing Pex5p, Pex5P had a dual location and was localized in th e cytosol and bound to the outer surface of the peroxisomal membrane. Our r esults indicate that binding of Pex5p to the peroxisomal membrane and impor t of certain PTS1 proteins can proceed in the absence of Pex14p.