Biology subjects

Krikken, A. M.

Publications and source records attributed to Krikken, A. M..

3 recordsLinked to original sources

bioRxiv2023

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

Pex23 family proteins are membrane proteins of the endoplasmic reticulum that play a role in peroxisome and lipid body formation. The yeast Hansenula polymorpha contains 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 in pex23 and pex29, but not in pex24 and pex32, indicating that peroxisome and lipid droplet formation require different Pex23 proteins. In pex23 and pex29 cells, 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 of DNM1 in pex23 cells partially suppressed the phenotype. Also, the level of the mitochondrial fusion protein Fzo1 was reduced in pex23 and pex29 cells. These observations indicate that certain Pex23 family proteins are required for normal mitochondrial fusion.

cell biology↗

bioRxiv2023

The Hansenula polymorpha Mitochondrial Carrier Family proteins Mir1 and Aac2 are dually localized at peroxisomes and mitochondria

Peroxisomes are ubiquitous cell organelles involved in various metabolic pathways. In order to properly function, several cofactors, substrates and products of peroxisomal enzymes need to pass the organellar membrane. So far only a few transporter proteins have been identified. We analysed peroxisomal membrane fractions purified from the yeast Hansenula polymorpha by untargeted label-free quantitation mass spectrometry. As expected, several known peroxisome-associated proteins were enriched in the peroxisomal membrane fraction. In addition, several other proteins were enriched, including mitochondrial transport proteins. Localization studies revealed that two of them, the mitochondrial carrier family proteins Aac2 and Mir1, have a dual localization on mitochondria and peroxisomes. To better understand the molecular mechanisms of dual sorting, we tested the localization of Mir1 in cells lacking Pex3 or Pex19, two peroxins that play a role in targeting of peroxisomal membrane proteins. In these cells Mir1 only localized to mitochondria, indicating that Pex3 and Pex19 are required to sort Mir1 to peroxisomes. Analysis of the localization of various truncated versions of Mir1 in wild-type H. polymorpha cells revealed that several localized to mitochondria, but only one, consisting of the transmembrane domains 3-6, was peroxisomal. Peroxisomal localization of this construct was lost in a MIR1 deletion strain, indicating that full length Mir1 was required for the localization of the truncated protein to peroxisomes. Our data suggest that only full length Mir1 sorts to peroxisomes, while Mir1 contains multiple regions with mitochondrial sorting information.

cell biology↗

bioRxiv2020

Pex24 and Pex32 tether peroxisomes to the ER for organelle biogenesis, positioning and segregation

We analyzed all four Pex23 family proteins of the yeast Hansenula polymorpha, which localize to the ER. Of these Pex24 and Pex32, but not Pex23 and Pex29, accumulate at peroxisome-ER contacts, where they are important for normal peroxisome biogenesis and proliferation and contribute to organelle positioning and segregation. Upon deletion of PEX24 and PEX32 - and to a lesser extent of PEX23 and PEX29 - peroxisome-ER contacts are disrupted, concomitant with peroxisomal defects. These defects are suppressed upon introduction of an artificial peroxisome-ER tether. Accumulation of Pex32 at peroxisomes-ER contacts is lost in the absence of the peroxisomal membrane protein Pex11. At the same time peroxisome-ER contacts are disrupted, indicating that Pex11 contributes to Pex32-dependent peroxisome-ER contact formation. Summarizing, our data indicate that H. polymorpha Pex24 and Pex32 are tethers at peroxisome-ER contacts that are important for normal peroxisome biogenesis and dynamics. SummaryTwo Hansenula polymorpha ER proteins, Pex24 and Pex32, are tethers at peroxisome-ER contacts and function together with the peroxisomal protein Pex11. Their absence disturbs these contacts leading to multiple peroxisomal defects, which can be restored by an artificial tether.

cell biology↗