The absence of yeast Pex23 and Pex29 results in a mitochondrial fusion defect

Abstract

AbstractPex23 family proteins are membrane proteins of the endoplasmic reticulum that play a role in peroxisome and lipid body formation. The yeastHansenula polymorphacontains four members: Pex23, Pex24, Pex29 and Pex32. We previously showed that the loss of Pex24 or Pex32 results in severe peroxisomal defects, caused by reduced peroxisome-endoplasmic reticulum membrane contact sites. We now analyzed whether the absence of Pex23 proteins affects other organelles. Vacuoles were normal in all deletion strains. The number of lipid droplets was reduced inpex23andpex29, but not inpex24andpex32, indicating that peroxisome and lipid droplet formation require different Pex23 proteins. Inpex23andpex29cells, mitochondria were fragmented and clustered. This phenotype was not suppressed by an artificial mitochondria-endoplasmic reticulum tether, indicating that the abnormalities were not caused by reduced membrane contact sites. Deletion ofDNM1inpex23cells partially suppressed the phenotype. Also, the level of the mitochondrial fusion protein Fzo1 was reduced inpex23andpex29cells. These observations indicate that certain Pex23 family proteins are required for normal mitochondrial fusion.