Maintaining Peroxisome Populations: A Story of Division and Inheritance
Eukaryotic cells divide their metabolic labor between functionally distinct, membrane-enveloped organelles, each precisely tailored for a specific set of biochemical reactions. Peroxisomes are ubiquitous, endoplasmic reticulum-derived organelles that perform requisite biochemical functions intimately connected to lipid metabolism. Upon cell division, cells have to strictly control peroxisome division and inheritance to maintain an appropriate number of peroxisomes in each cell. Peroxisome division follows a specific sequence of events that include peroxisome elongation, membrane constriction, and peroxisome fission. Pex11 proteins mediate the elongation step of peroxisome division, whereas dynamin-related proteins execute the final fission. The mechanisms responsible for peroxisome membrane constriction are poorly understood. Molecular players involved in peroxisome inheritance are just beginning to be elucidated. Inp1p and Inp2p are two recently identified peroxisomal proteins that perform antagonistic functions in regulating peroxisome inheritance in budding yeast. Inp1p promotes the retention of peroxisomes in mother cells and buds by attaching peroxisomes to as-yet-unidentified cortical structures. Inp2p is implicated in the motility of peroxisomes by linking them to the Myo2p motor, which then propels their movement along actin cables. The functions of Inp1p and Inp2p are cell cycle regulated and coordinated to ensure a fair distribution of peroxisomes at cytokinesis.
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- "Peroxisomes are organelles found in all eukaryotic cells from unicellular eukaryotes such as algae and baker's yeast to complex multicellular organisms such as humans and flowering plants. Peroxisomes can be derived from the endoplasmic reticulum (ER) but can grow by post-translational import of membrane and matrix proteins, divide and segregate into daughter cells (Fagarasanu et al., 2007) However, the relative importance of de novo biogenesis versus organelle division remains hotly debated (Hettema et al., 2014) and it should be noted that in plants no direct evidence for ER luminal connections has been found (Barton et al., 2013). Peroxisomes are also capable of proliferation under appropriate environmental conditions. "
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ABSTRACT: Peroxisomal biogenesis factor 11 (PEX11) proteins are found in yeasts, mammals and plants, and play a role in peroxisome morphology and regulation of peroxisome division. The moss Physcomitrella patens has six PEX11 isoforms which fall into two subfamilies, similar to those found in monocots and dicots. We carried out targeted gene disruption of the Phypa_PEX11-1 gene and compared the morphological and cellular phenotypes of the wild-type and mutant strains. The mutant grew more slowly and the development of gametophores was retarded. Mutant chloronemal filaments contained large cellular structures which excluded all other cellular organelles. Expression of fluorescent reporter proteins revealed that the mutant strain had greatly enlarged peroxisomes up to 10 μm in diameter. Expression of a vacuolar membrane marker confirmed that the enlarged structures were not vacuoles, or peroxisomes sequestered within vacuoles as a result of pexophagy. Phypa_PEX11 targeted to peroxisome membranes could rescue the knock out phenotype and interacted with Fission1 on the peroxisome membrane. Moss PEX11 functions in peroxisome division similar to PEX11 in other organisms but the mutant phenotype is more extreme and environmentally determined, making P. patens a powerful system in which to address mechanisms of peroxisome proliferation and division.
Available from: Sarah Jane Butcher
- "Peroxisomes are single-membrane organelles varying in size, shape, and biochemical content depending on cell type and environmental requirements –. The importance of peroxisomes for normal mammalian development has been shown by their linkage to many inherited diseases. "
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ABSTRACT: In peroxisomes, peroxins (PEXs) 3 and 19 are the principal protein components of the machinery required for early peroxisomal biogenesis. For further insight into the interaction of PEX3 and PEX19, we used hydrogen exchange mass spectrometry to monitor conformational changes during complex formation between PEX3 and PEX19 in vitro. Our data showed that PEX19 remained highly flexible during interaction with PEX3. However, we could detect three changes, one each in the N-and C-terminus along with a small stretch in the middle of PEX19 (F64-L74) which became shielded from hydrogen exchange when interacting with PEX3. PEX3 became more protected from hydrogen exchange in the binding groove for PEX19 with only small changes elsewhere. Most likely the N-terminus of PEX19 initiates the binding to PEX3, and then subtle conformational changes in PEX3 affect the surface of the PEX3 molecule. PEX19 in turn, is stabilized by folding of a short helix and its C-terminal folding core permitting PEX19 to bind to PEX3 with higher affinity than just the N-terminal interaction allows. Thus within the cell, PEX3 is stabilized by PEX19 preventing PEX3 aggregation.
Available from: sciencedirect.com
- "During cell division, cells control the partition of organelles to the mother and daughter cell, to guarantee that both receive their required quota of organelles. Two proteins in yeast, termed inheritance of peroxisomes protein (Inp) 1 and 2, have important but opposite functions during organelle partition . Overexpression of Inp1 causes an increase in the number of daughter cells without peroxisomes, due to its function in "
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ABSTRACT: Peroxisomes play a crucial role in regulating cellular metabolism, providing compartments where metabolic pathways can be contained and controlled. Their importance is underlined by the developmental brain disorders caused by peroxisome malfunction, while disturbances in peroxisome function also contribute to ageing. As peroxisomes do not contain DNA, they rely on an active transport system to obtain the full quota of proteins required for function. Organelle protein transport however, is rarely a one-way process and exciting recent data have demonstrated that peroxisomes can selectively export membrane and matrix proteins to fulfil specific functions. This review will summarize the current knowledge on peroxisomal membrane and matrix protein export, discussing the mechanisms underlying export as well as the role of peroxisomal protein export in peroxisomal and cellular function.
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