Determinants of the assembly, integrity and maintenance of the endoplasmic reticulum‐peroxisome tether

Abstract

Organelle tethering and intercommunication are crucial for proper cell function. We previously described a tether between peroxisomes and the endoplasmic reticulum (ER) that acts in peroxisome population control in the yeast, Saccharomyces cerevisiae. Components of this tether are Pex3p, an integral membrane protein of both peroxisomes and the ER and Inp1p, a connector that links peroxisomes to the ER. Here, we report the analysis of random Inp1p mutants that enabled identification of regions in Inp1p required for the assembly and maintenance of the ER‐peroxisome tether. Interaction analysis between Inp1p mutants and known Inp1p‐binding proteins demonstrated that Pex3p and Inp1p do not constitute the sole components of the ER‐peroxisome tether. Deletion of these Inp1p interactors whose steady‐state localization is outside of ER‐peroxisome tethers affected peroxisome dynamics. Our findings are consistent with the presence of regulatory cues that act on ER‐peroxisome tethers and point to the existence of membrane contact sites between peroxisomes and organelles other than the ER.

The Pex3–Inp1 complex tethers yeast peroxisomes to the plasma membrane

“…Inp1 is in the correct subcellular location to be a PM-PER tether During cell division, a subset of peroxisomes are retained by cortical anchoring in the mother cell (Fagarasanu et al, 2005;Hoepfner et al, 2001;Knoblach and Rachubinski, 2019;Knoblach et al, 2013). Though the role of the cER in peroxisome retention has been reported, the role of the plasma membrane remains unexplored.…”

“…During the course of our study, an independent study reported a random Inp1 mutant in this motif (LXXLP). This mutant also blocked recruitment of Inp1 to peroxisomes and interfered with Inp1 function (Knoblach and Rachubinski, 2019).…”

“…The Inp1-Pex3 tethering complex is required for peroxisome retention during cell division and for peroxisome positioning along the mother cortex (Fagarasanu et al, 2005;Knoblach and Rachubinski, 2013;Munck et al, 2009). As has been postulated for other organelles, yeast peroxisomes interact with many cellular structures, including the plasma membrane, ER, vacuole, mitochondria, and lipid bodies (Eisenberg-Bord et al, 2016;Knoblach and Rachubinski, 2019;Wu et al, 2019). Components of some interorganellar peroxisomal contact sites have recently been identified whereas others are still completely uncharacterized, including the plasma membrane-peroxisome (PM-PER) contact site (Shai et al, 2016).…”

“…The existence of PM-PER contact sites has been reported (Shai et al, 2018), but as yet, these remain uncharacterized. Previously, peroxisomes have been reported to be retained via Inp1 and the cER; however, a recent study suggests that additional components are required for peroxisome tethering to the cell cortex (Knoblach and Rachubinski, 2019;Knoblach et al, 2013). Through detailed analysis of the molecular function of Inp1, we have uncovered a novel role for Inp1 as a PM-PER tether and conclude that tethering of peroxisomes to the plasma membrane is required for peroxisome retention.…”

Peroxisome retention involves Inp1-dependent peroxisome–plasma membrane contact sites in yeast

“…S. cerevisiae Inp1 tethers peroxisomes to the cortex of mother cells, but also is important for capturing organelles in buds (Fagarasanu et al, 2005). Inp1 is a soluble protein that is recruited to peroxisomes by the PMP Pex3 (Munck et al, 2009;Knoblach et al, 2013;Knoblach and Rachubinski, 2019). It mainly associates to mature peroxisomes that are retained in mother cells.…”