Peroxisome biogenesis involves a number of proteins, the so-called peroxins. Most peroxins are peroxisomal, but members of the Pex23 family localise to the ER and are thought to be involved in the formation ER–peroxisome contacts, although roles at other organelles have been described. However, only some of the Pex23 proteins have been studied extensively, mostly in a few yeast species, and our knowledge of the Pex23 family thus remains scarce. In this work, Ida van der Klei and colleagues (Wu, de Boer et al., 2020) set out to study all four Pex23 members of the yeast Hansenula polymorpha. They first show that, although all four Pex23 proteins localise to the ER, only Pex24 and Pex32 accumulate at ER–peroxisome contacts, but not Pex23 and Pex29. Accordingly, knockdown of pex24 or pex32 results in loss of ER–peroxisome contacts and extensive peroxisomal defects, including in peroxisome biogenesis, segregation and positioning within the cell. These defects could be rescued with an artificial ER–peroxisome tether, indicating that Pex24 and Pex32 are involved in tethering these organelles. Furthermore, localisation of Pex32 to ER–peroxisome contacts requires the peroxisomal membrane protein Pex11. Taken together, these findings present the first characterisation of the entire Pex23 family in a species, and will help to further elucidate their exact molecular functions in peroxisome biology.
