The Hansenula polymorpha peroxisomal targeting signal 1 receptor, Pex5p, functions as a tetramer.

We have studied Hansenula polymorpha Pex5p and Pex20p, peroxins involved in peroxisomal matrix protein import. In vitro binding experiments suggested that H. polymorpha Pex5p and Pex20p physically interact. We used single particle electron microscopy (EM) to analyze the structure of purified Pex5p and its possible association with Pex20p. Upon addition of Pex20p, a multimeric Pex20p complex was observed to be associated to the periphery of the Pex5p tetramer. In this Pex5p-Pex20p complex, the conformation of tetrameric Pex5p had changed from a closed conformation with a diameter of 115A into an open conformation of 134A. EM also indicated that the Pex5p-Pex20p complex was capable to bind native, folded catalase, a peroxisomal PTS1 protein. This suggests that the Pex5p-Pex20p complex may be functional as receptor complex.