The Experts below are selected from a list of 114 Experts worldwide ranked by ideXlab platform
Suresh Subramani - One of the best experts on this subject based on the ideXlab platform.
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Atg35, a Micropexophagy-specific protein that regulates micropexophagic apparatus formation in Pichia pastoris.
Autophagy, 2011Co-Authors: Volodymyr Y. Nazarko, Jeanclaude Farre, Dirk Warnecke, Andrei Sibirny, Taras Y. Nazarko, Oleh V. Stasyk, Stanislaw Ulaszewski, James M. Cregg, Suresh SubramaniAbstract:Autophagy-related (Atg) pathways deliver cytosol and organelles to the vacuole in double-membrane vesicles called autophagosomes, which are formed at the phagophore assembly site (PAS), where most of the core Atg proteins assemble. Atg28 is a component of the core autophagic machinery partially required for all Atg pathways in Pichia pastoris. This coiled-coil protein interacts with Atg17 and is essential for Micropexophagy. However, the role of Atg28 in Micropexophagy was unknown. We used the yeast two-hybrid system to search for Atg28 interaction partners from P. pastoris and identified a new Atg protein, named Atg35. The atg35∆ mutant was not affected in macropexophagy, cytoplasm-to-vacuole targeting or general autophagy. However, both Atg28 and Atg35 were required for Micropexophagy and for the formation of the micropexophagic apparatus (MIPA). This requirement correlated with a stronger expression of both proteins on methanol and glucose. Atg28 mediated the interaction of Atg35 with Atg17. Traffickin...
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Molecular mechanism and physiological role of pexophagy
FEBS letters, 2010Co-Authors: Ravi Manjithaya, Jeanclaude Farre, Taras Y. Nazarko, Suresh SubramaniAbstract:Pexophagy is a selective autophagy process wherein damaged and/or superfluous peroxisomes undergo vacuolar degradation. In methylotropic yeasts, where pexophagy has been studied most extensively, this process occurs by either micro- or macropexophagy: processes analogous to micro- and macroautophagy. Recent studies have identified specific factors and illustrated mechanisms involved in pexophagy. Although mechanistically pexophagy relies heavily on the core autophagic machinery, the latest findings about the role of auxiliary pexophagy factors have highlighted specialized membrane structures required for Micropexophagy, and shown how cargo selectivity is achieved and how cargo size dictates the requirement for these factors during pexophagy. These insights and additional observations in the literature provide a framework for an understanding of the physiological role(s) of pexophagy.
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ppatg30 tags peroxisomes for turnover by selective autophagy
Developmental Cell, 2008Co-Authors: Jeanclaude Farre, Ravi Manjithaya, Richard D Mathewson, Suresh SubramaniAbstract:Autophagy, an intrinsically nonselective process, can also target selective cargo for degradation. The mechanism of selective peroxisome turnover by autophagy-related processes (pexophagy), termed Micropexophagy and macropexophagy, is unknown. We show how a Pichia pastoris protein, PpAtg30, mediates peroxisome selection during pexophagy. It is necessary for pexophagy, but not for other selective and nonselective autophagy-related processes. It localizes at the peroxisome membrane via interaction with peroxins, and during pexophagy it colocalizes transiently at the preautophagosomal structure (PAS) and interacts with the autophagy machinery. PpAtg30 is required for formation of pexophagy intermediates, such as the Micropexophagy apparatus (MIPA) and the pexophagosome (Ppg). During pexophagy, PpAtg30 undergoes multiple phosphorylations, at least one of which is required for pexophagy. PpAtg30 overexpression stimulates pexophagy even under peroxisome-induction conditions, impairing peroxisome biogenesis. Therefore, PpAtg30 is a key player in the selection of peroxisomes as cargo and in their delivery to the autophagy machinery for pexophagy.
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The membrane dynamics of pexophagy are influenced by sarlp in Pichia pastoris
2008Co-Authors: Laura A. Schroder, William A. Dunn, Michael V. Ortiz, Suresh SubramaniAbstract:Several Sec proteins including a guanosine diphosphate/guanosine triphosphate exchange factor for Sar1p have been implicated in autophagy. In this study, we investigated the role of Sar1p in pexophagy by expressing dominant-negative mutant forms of Sar1p in Pichia pastoris. When expressing sar1pT34N or sar1pH79G, starvation-induced autophagy, glucose-induced Micropexophagy, and ethanol-induced macropexophagy are dramatically suppressed. These Sar1p mutants did not affect the initiation or expansion of the sequestering membranes nor the trafficking of Atg11p and Atg9p to these membranes during Micropexophagy. However, the lipidation of Atg8p and assembly of the micropexophagic membrane apparatus, which are essential to complete the incorporation of the peroxisomes into the degradative vacuole, were inhibited when either Sar1p mutant protein was expressed. During macropexophagy, the expression of sar1pT34N inhibited the formation of the pexophagosome, whereas sar1pH79G suppressed the delivery of the peroxisome from the pexophagosome to the vacuole. The pexophagosome contained Atg8p in wild-type cells, but in cells expressing sar1pH79G these organelles contain both Atg8p and endoplasmic reticulum components as visualized by DsRFP-HDEL. Our results demonstrate key roles for Sar1p in both micro- and macropexophagy
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Autophagy-related pathways and specific role of sterol glucoside in yeasts.
Autophagy, 2007Co-Authors: Taras Y. Nazarko, Jeanclaude Farre, Andrei Sibirny, Andriy S. Polupanov, Suresh SubramaniAbstract:Recently, we showed that the requirement of sterol glucoside (SG) during pexophagy in yeasts is dependent on the species and the nature of peroxisome inducers. Atg26, the enzyme that converts sterol to SG, is essential for degradation of very large methanol-induced peroxisomes, but only partly required for degradation of smaller-sized oleate- and amine-induced peroxisomes in Pichia pastoris. Moreover, oleate- and amine-induced peroxisomes of another yeast, Yarrowia lipolytica, are degraded by an Atg26-independent mechanism. The same is true for degradation of oleate-induced peroxisomes in Saccharomyces cerevisiae. Here, we review our findings on the specificity of Atg26 function in pexophagy and extend our observations to the role of SG in the cytoplasm to vacuole targeting (Cvt) pathway and bulk autophagy. The results presented here and elsewhere indicate that Atg26 might increase the efficacy of all autophagy-related pathways in P. pastoris, but not in other yeasts. Recently, it was shown that P. pastoris Atg26 (PpAtg26) is required for elongation of the pre-autophagosomal structure (PAS) into the micropexophagic membrane apparatus (MIPA) during Micropexophagy. Therefore, we speculate that SG might facilitate elongation of any double membrane from the PAS and this enhancer function of SG becomes essential when extremely large double membranes are formed.
Yasuyoshi Sakai - One of the best experts on this subject based on the ideXlab platform.
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atg21 regulates pexophagy via its pi 3 p binding activity in pichia pastoris
Fems Yeast Research, 2014Co-Authors: Naoki Tamura, Masahide Oku, Yasuyoshi SakaiAbstract:Pexophagy is a selective degradation pathway of peroxisomes. In the present study, we revealed that PpAtg21 was required for pexophagy in the methylotrophic yeast Pichia pastoris. PpAtg21 was essential for efficient lipidation of Atg8 and for de novo synthesis of pexophagic membranes. In contrast to PpAtg18, PpAtg21 was not necessary for vacuolar fission nor invagination during Micropexophagy. PpAtg21 specifically bound to PI(3)P, but not to PI(3,5)P2 in vitro, and the localization analyses matched with this phosphoinositide-binding specificity. The mutant which lost the lipid-binding activity showed defect in pexophagy, suggesting that PI(3)P-binding activity of PpAtg21 was required for pexophagy.
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Pexophagy: autophagic degradation of peroxisomes.
Biochimica et Biophysica Acta, 2006Co-Authors: Yasuyoshi Sakai, Ida J. Van Der Klei, Jan A.k.w. KielAbstract:The abundance of peroxisomes within a cell can rapidly decrease by selective autophagic degradation (also designated pexophagy). Studies in yeast species have shown that at least two modes of peroxisome degradation are employed, namely macropexophagy and Micropexophagy. During macropexophagy, peroxisomes are individually sequestered by membranes, thus forming a pexophagosome. This structure fuses with the vacuolar membrane, resulting in exposure of the incorporated peroxisome to vacuolar hydrolases. During Micropexophagy, a cluster of peroxisomes is enclosed by vacuolar membrane protrusions and/or segmented vacuoles as well as a newly formed membrane structure, the Micropexophagy-specific membrane apparatus (MIPA), which mediates the enclosement of the vacuolar membrane. Subsequently, the engulfed peroxisome cluster is degraded. This review discusses the current state of knowledge of pexophagy with emphasis on studies on methylotrophic yeast species.
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role of vac8 in formation of the vacuolar sequestering membrane during Micropexophagy
Autophagy, 2006Co-Authors: Masahide Oku, Yoshitaka Ano, Takeshi Hattori, Taku Nishimura, Shunichi Yamashita, Yasuyoshi SakaiAbstract:Vac8 is a yeast vacuolar membrane protein involved in vacuolar membrane dynamics, e.g., vacuole inheritance and vacuolar membrane fusion. This protein is also necessary for a subset of autophagic pathways that deliver specific cellular components to the vacuole. In this study, we show that the micropexohagy and vacuole inheritance required distinct domain structures of Pichia pastoris Vac8 (PpVac8). Whereas vacuole inheritance required the Armadillo repeat (ARM) region that resides in the middle part of the protein, Micropexophagy did not. Deletion of both the ARM and C-terminal domains inhibited a characteristic of vacuolar dynamics during Micropexophagy, i.e., formation of the vacuolar sequestering membrane (VSM). Subsequent analyses indicated that PpVAC8 disruption abolished recruitment of PpAtg11, another protein required for formation of the VSM, to the vacuolar membrane. These results present a novel molecular function of PpVac8 in Micropexophagy.
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A Sorting Nexin PpAtg24 Regulates Vacuolar Membrane Dynamics during Pexophagy via Binding to Phosphatidylinositol-3-Phosphate
Molecular biology of the cell, 2004Co-Authors: Yoshitaka Ano, Hiroyuki Mukaiyama, Nobuo Kato, Misuzu Baba, Yoshinori Ohsumi, Masahide Oku, Takeshi Hattori, Yasuyoshi SakaiAbstract:Diverse cellular processes such as autophagic protein degradation require phosphoinositide signaling in eukaryotic cells. In the methylotrophic yeast Pichia pastoris, peroxisomes can be selectively degraded via two types of pexophagic pathways, macropexophagy and Micropexophagy. Both involve membrane fusion events at the vacuolar surface that are characterized by internalization of the boundary domain of the fusion complex, indicating that fusion occurs at the vertex. Here, we show that PpAtg24, a molecule with a phosphatidylinositol 3-phosphate-binding module (PX domain) that is indispensable for pexophagy, functions in membrane fusion at the vacuolar surface. CFP-tagged PpAtg24 localized to the vertex and boundary region of the pexophagosome-vacuole fusion complex during macropexophagy. Depletion of PpAtg24 resulted in the blockage of macropexophagy after pexophagosome formation and before the fusion stage. These and other results suggest that PpAtg24 is involved in the spatiotemporal regulation of membrane fusion at the vacuolar surface during pexophagy via binding to phosphatidylinositol 3-phosphate, rather than the previously suggested function in formation of the pexophagosome.
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Modification of a ubiquitin-like protein Paz2 conducted Micropexophagy through formation of a novel membrane structure.
Molecular Biology of the Cell, 2003Co-Authors: Hiroyuki Mukaiyama, Satoshi Aoyagi, Nobuo Kato, Misuzu Baba, Yoshinori Ohsumi, Masako Osumi, Yasuyoshi SakaiAbstract:Microautophagy is a versatile process in which vacuolar or lysosomal membranes directly sequester cytosolic targets for degradation. Recent genetic evidence suggested that microautophagy uses molecular machineries essential for macroautophagy, but the details of this process are still unknown. In this study, a ubiquitin-like protein Paz2 essential for Micropexophagy in the yeast Pichia pastoris has been shown to receive modification through the function of Paz8 and Gsa7, yielding a modified form Paz2-I, similar to the ubiquitin-like lipidation of Aut7 that is essential for macroautophagy in Saccharomyces cerevisiae. We identified a novel membrane structure formed after the onset of Micropexophagy, which we suggest is necessary for the sequestration of peroxisomes by the vacuole. Assembly of this newly formed membrane structure, which is followed by localization of Paz2 to it, was found to require a properly functioning Paz2-modification system. We herein show that Paz2 and its modification system conduct Micropexophagy through formation of the membrane structure, which explains the convergence between Micropexophagy and macroautophagy with regard to de novo membrane formation.
Jeanclaude Farre - One of the best experts on this subject based on the ideXlab platform.
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Atg35, a Micropexophagy-specific protein that regulates micropexophagic apparatus formation in Pichia pastoris.
Autophagy, 2011Co-Authors: Volodymyr Y. Nazarko, Jeanclaude Farre, Dirk Warnecke, Andrei Sibirny, Taras Y. Nazarko, Oleh V. Stasyk, Stanislaw Ulaszewski, James M. Cregg, Suresh SubramaniAbstract:Autophagy-related (Atg) pathways deliver cytosol and organelles to the vacuole in double-membrane vesicles called autophagosomes, which are formed at the phagophore assembly site (PAS), where most of the core Atg proteins assemble. Atg28 is a component of the core autophagic machinery partially required for all Atg pathways in Pichia pastoris. This coiled-coil protein interacts with Atg17 and is essential for Micropexophagy. However, the role of Atg28 in Micropexophagy was unknown. We used the yeast two-hybrid system to search for Atg28 interaction partners from P. pastoris and identified a new Atg protein, named Atg35. The atg35∆ mutant was not affected in macropexophagy, cytoplasm-to-vacuole targeting or general autophagy. However, both Atg28 and Atg35 were required for Micropexophagy and for the formation of the micropexophagic apparatus (MIPA). This requirement correlated with a stronger expression of both proteins on methanol and glucose. Atg28 mediated the interaction of Atg35 with Atg17. Traffickin...
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Molecular mechanism and physiological role of pexophagy
FEBS letters, 2010Co-Authors: Ravi Manjithaya, Jeanclaude Farre, Taras Y. Nazarko, Suresh SubramaniAbstract:Pexophagy is a selective autophagy process wherein damaged and/or superfluous peroxisomes undergo vacuolar degradation. In methylotropic yeasts, where pexophagy has been studied most extensively, this process occurs by either micro- or macropexophagy: processes analogous to micro- and macroautophagy. Recent studies have identified specific factors and illustrated mechanisms involved in pexophagy. Although mechanistically pexophagy relies heavily on the core autophagic machinery, the latest findings about the role of auxiliary pexophagy factors have highlighted specialized membrane structures required for Micropexophagy, and shown how cargo selectivity is achieved and how cargo size dictates the requirement for these factors during pexophagy. These insights and additional observations in the literature provide a framework for an understanding of the physiological role(s) of pexophagy.
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ppatg30 tags peroxisomes for turnover by selective autophagy
Developmental Cell, 2008Co-Authors: Jeanclaude Farre, Ravi Manjithaya, Richard D Mathewson, Suresh SubramaniAbstract:Autophagy, an intrinsically nonselective process, can also target selective cargo for degradation. The mechanism of selective peroxisome turnover by autophagy-related processes (pexophagy), termed Micropexophagy and macropexophagy, is unknown. We show how a Pichia pastoris protein, PpAtg30, mediates peroxisome selection during pexophagy. It is necessary for pexophagy, but not for other selective and nonselective autophagy-related processes. It localizes at the peroxisome membrane via interaction with peroxins, and during pexophagy it colocalizes transiently at the preautophagosomal structure (PAS) and interacts with the autophagy machinery. PpAtg30 is required for formation of pexophagy intermediates, such as the Micropexophagy apparatus (MIPA) and the pexophagosome (Ppg). During pexophagy, PpAtg30 undergoes multiple phosphorylations, at least one of which is required for pexophagy. PpAtg30 overexpression stimulates pexophagy even under peroxisome-induction conditions, impairing peroxisome biogenesis. Therefore, PpAtg30 is a key player in the selection of peroxisomes as cargo and in their delivery to the autophagy machinery for pexophagy.
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Autophagy-related pathways and specific role of sterol glucoside in yeasts.
Autophagy, 2007Co-Authors: Taras Y. Nazarko, Jeanclaude Farre, Andrei Sibirny, Andriy S. Polupanov, Suresh SubramaniAbstract:Recently, we showed that the requirement of sterol glucoside (SG) during pexophagy in yeasts is dependent on the species and the nature of peroxisome inducers. Atg26, the enzyme that converts sterol to SG, is essential for degradation of very large methanol-induced peroxisomes, but only partly required for degradation of smaller-sized oleate- and amine-induced peroxisomes in Pichia pastoris. Moreover, oleate- and amine-induced peroxisomes of another yeast, Yarrowia lipolytica, are degraded by an Atg26-independent mechanism. The same is true for degradation of oleate-induced peroxisomes in Saccharomyces cerevisiae. Here, we review our findings on the specificity of Atg26 function in pexophagy and extend our observations to the role of SG in the cytoplasm to vacuole targeting (Cvt) pathway and bulk autophagy. The results presented here and elsewhere indicate that Atg26 might increase the efficacy of all autophagy-related pathways in P. pastoris, but not in other yeasts. Recently, it was shown that P. pastoris Atg26 (PpAtg26) is required for elongation of the pre-autophagosomal structure (PAS) into the micropexophagic membrane apparatus (MIPA) during Micropexophagy. Therefore, we speculate that SG might facilitate elongation of any double membrane from the PAS and this enhancer function of SG becomes essential when extremely large double membranes are formed.
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atg28 a novel coiled coil protein involved in autophagic degradation of peroxisomes in the methylotrophic yeast pichia pastoris
Autophagy, 2006Co-Authors: Jeanclaude Farre, Richard D Mathewson, Suresh Subramani, Volodymyr Y. Nazarko, Oleh V. Stasyk, Olena S Krasovska, James M. CreggAbstract:In methylotrophic yeasts, peroxisomes are required for methanol utilization, but are dispensable for growth on most other carbon sources. Upon adaptation of cells grown on methanol to glucose or ethanol, redundant peroxisomes are selectively and quickly shipped to, and degraded in, vacuoles via a process termed pexophagy. We identified a novel gene named ATG28 (autophagy-related genes) involved in pexophagy in the yeast Pichia pastoris. This yeast exhibits two morphologically distinct pexophagy pathways, micro- and macropexophagy, induced by glucose or ethanol, respectively. Deficiency in ATG28 impairs both pexophagic mechanisms but not general (bulk turnover) autophagy, a degradation pathway in yeast triggered by nitrogen starvation. It is known that the micro-, macropexophagy, and general autophagy machineries are distinct but share some molecular components. The identification of ATG28 suggests that pexophagy may involve species-specific components, since this gene appears to have only weak homologues in other yeasts.
Oleh V. Stasyk - One of the best experts on this subject based on the ideXlab platform.
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Atg35, a Micropexophagy-specific protein that regulates micropexophagic apparatus formation in Pichia pastoris.
Autophagy, 2011Co-Authors: Volodymyr Y. Nazarko, Jeanclaude Farre, Dirk Warnecke, Andrei Sibirny, Taras Y. Nazarko, Oleh V. Stasyk, Stanislaw Ulaszewski, James M. Cregg, Suresh SubramaniAbstract:Autophagy-related (Atg) pathways deliver cytosol and organelles to the vacuole in double-membrane vesicles called autophagosomes, which are formed at the phagophore assembly site (PAS), where most of the core Atg proteins assemble. Atg28 is a component of the core autophagic machinery partially required for all Atg pathways in Pichia pastoris. This coiled-coil protein interacts with Atg17 and is essential for Micropexophagy. However, the role of Atg28 in Micropexophagy was unknown. We used the yeast two-hybrid system to search for Atg28 interaction partners from P. pastoris and identified a new Atg protein, named Atg35. The atg35∆ mutant was not affected in macropexophagy, cytoplasm-to-vacuole targeting or general autophagy. However, both Atg28 and Atg35 were required for Micropexophagy and for the formation of the micropexophagic apparatus (MIPA). This requirement correlated with a stronger expression of both proteins on methanol and glucose. Atg28 mediated the interaction of Atg35 with Atg17. Traffickin...
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The role of Hansenula polymorpha MIG1 homologues in catabolite repression and pexophagy
FEMS yeast research, 2007Co-Authors: Tim Van Zutphen, Oleh V. Stasyk, Huyn Ah Kang, Marten Veenhuis, Andrei SibirnyAbstract:In the methanol-utilizing yeast Hansenula polymorpha, glucose and ethanol trigger the repression of peroxisomal enzymes at the transcriptional level, and rapid and selective degradation of methanol-induced peroxisomes by means of a process termed pexophagy. In this report we demonstrate that deficiency in the putative H. polymorpha homologues of transcriptional repressors Mig1 (HpMig1 and HpMig2), as well as HpTup1, partially and differentially affects the repression of peroxisomal alcohol oxidase by sugars and ethanol. As reported earlier, deficiency in HpTup1 leads to impairment of glucose- or ethanol-induced macropexophagy. In H. polymorpha mig1mig2 double-deletion cells, macropexophagy was also substantially impaired, whereas Micropexophagy became a dominant mode of autophagic degradation. Our findings suggest that homologues of the elements of the Saccharomyces cerevisiae main repression pathway have pleiotropic functions in H. polymorpha.
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First published online August 2007. DOI:10.1111/j.1567-1364.2007.00286.x
2007Co-Authors: Andrei Sibirny, Oleh V. Stasyk, Tim Van Zutphen, Huyn Ah Kang, Marten Veenhuis, Correspondence Andriy A. Sibirny, Gerd GellissenAbstract:repressors. In the methanol-utilizing yeast Hansenula polymorpha, glucose and ethanol trigger the repression of peroxisomal enzymes at the transcriptional level, and rapid and selective degradation of methanol-induced peroxisomes by means of a process termed pexophagy. In this report we demonstrate that deficiency in the putative H. polymorpha homologues of transcriptional repressors Mig1 (HpMig1 and HpMig2), as well as HpTup1, partially and differentially affects the repression of peroxisomal alcohol oxidase by sugars and ethanol. As reported earlier, deficiency in HpTup1 leads to impairment of glucose- or ethanol-induced macropexophagy. In H. polymorpha mig1mig2 double-deletion cells, macropexophagy was also substantially impaired, whereas Micropexophagy became a dominant mode of autophagic degradation. Our findings suggest that homologues of the elements of the Saccharomyces cerevisiae main repression pathway have pleiotropic functions in H. polymorpha
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atg28 a novel coiled coil protein involved in autophagic degradation of peroxisomes in the methylotrophic yeast pichia pastoris
Autophagy, 2006Co-Authors: Jeanclaude Farre, Richard D Mathewson, Suresh Subramani, Volodymyr Y. Nazarko, Oleh V. Stasyk, Olena S Krasovska, James M. CreggAbstract:In methylotrophic yeasts, peroxisomes are required for methanol utilization, but are dispensable for growth on most other carbon sources. Upon adaptation of cells grown on methanol to glucose or ethanol, redundant peroxisomes are selectively and quickly shipped to, and degraded in, vacuoles via a process termed pexophagy. We identified a novel gene named ATG28 (autophagy-related genes) involved in pexophagy in the yeast Pichia pastoris. This yeast exhibits two morphologically distinct pexophagy pathways, micro- and macropexophagy, induced by glucose or ethanol, respectively. Deficiency in ATG28 impairs both pexophagic mechanisms but not general (bulk turnover) autophagy, a degradation pathway in yeast triggered by nitrogen starvation. It is known that the micro-, macropexophagy, and general autophagy machineries are distinct but share some molecular components. The identification of ATG28 suggests that pexophagy may involve species-specific components, since this gene appears to have only weak homologues in other yeasts.
Ida J. Van Der Klei - One of the best experts on this subject based on the ideXlab platform.
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damaged peroxisomes are subject to rapid autophagic degradation in the yeast hansenula polymorpha
Autophagy, 2011Co-Authors: Tim Van Zutphen, Ida J. Van Der KleiAbstract:Evidence is accumulating that damaged components of eukaryotic cells are removed by autophagic degradation (e.g., mitophagy). Here we show that peroxisomes that are damaged by the abrupt removal of the membrane protein Pex3 are massively and rapidly degraded even when the cells are placed at peroxisome-inducing conditions and hence need the organelles for growth. Pex3 degradation was induced by a temperature shift using Hansenula polymorpha pex3Δ cells producing a Pex3 fusion protein containing an N-terminal temperature sensitive degron sequence. The massive peroxisome degradation process, associated with Pex3 degradation, showed properties of both micro- and macropexophagy and was dependent on Atg1 and Ypt7. This mode of peroxisome degradation is of physiological significance as it was also observed at conditions that excessive ROS is formed from peroxisome metabolism, i.e., when methanol-grown wild-type cells are exposed to methanol excess conditions.
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the hansenula polymorpha atg25 gene encodes a novel coiled coil protein that is required for macropexophagy
Autophagy, 2005Co-Authors: Iryna Monastyrska, Jan A.k.w. Kiel, Janet Komduur, Arjen M Krikken, Ida J. Van Der KleiAbstract:We have isolated the Hansenula polymorpha ATG25 gene, which is required for glucose-induced selective peroxisome degradation by macropexophagy. ATG25 represents a novel gene that encodes a 45 kDa coiled-coil protein. We show that this protein colocalizes with Atg11 on a small structure, which most likely represents the pre-autophagosomal structure (PAS). In cells of a constructed ATG25 deletion strain (atg25) peroxisomes are constitutively degraded by nonselective microautophagy, a process that in WT H. polymorpha is only observed at nitrogen limitation conditions. This suggests that nonselective microautophagy is deregulated in H. polymorpha atg25 cells.
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atg8 is essential for macropexophagy in hansenula polymorpha
Traffic, 2005Co-Authors: Iryna Monastyrska, Jan A.k.w. Kiel, Arjen M Krikken, Meis Van Der Heide, Ida J. Van Der KleiAbstract:We have isolated a peroxisome-degradation-deficient (pdd) mutant of the methylotrophic yeast Hansenula polymorpha via gene tagging mutagenesis. Sequencing revealed that the mutant was affected in the HpATG8 gene. HpAtg8 is a protein with high sequence similarity to both Pichia pastoris and Saccharomyces cerevisiae Atg8 and appeared to be essential for selective peroxisome degradation (macropexophagy) and nitrogen-limitation induced microautophagy. Fluorescence microscopy revealed that a GFP.Atg8 fusion protein was located close to the vacuole. After induction of macropexophagy, the GFP.Atg8 containing spot extended to engulf an individual peroxisome. In cells of a constructed deletion strain, sequestration of individual organelles was never completed; analysis of series of serial sections revealed that invariably a minor diaphragm-like opening remained. We hypothesize that H. polymorpha Atg8 facilitates sealing of the sequestering membranes during selective peroxisome degradation.
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macropexophagy in hansenula polymorpha facts and views
FEBS Letters, 2003Co-Authors: Jan A.k.w. Kiel, Janet Komduur, Ida J. Van Der KleiAbstract:The hallmark of eukaryotic cells is compartmentalization of distinct cellular functions into specific organelles. This necessitates the cells to run energetically costly mechanisms to precisely control maintenance and function of these compartments. One of these continuously controls organelle activity and abundance, a process termed homeostasis. Yeast peroxisomes are favorable model systems for studies of organelle homeostasis because both the proliferation and degradation of these organelles can be readily manipulated. Here, we highlight recent achievements in regulation of peroxisome turnover in yeast, in particular Hansenula polymorpha, with a focus on directions of future research.
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removal of pex3p is an important initial stage in selective peroxisome degradation in hansenula polymorpha
Journal of Biological Chemistry, 2002Co-Authors: Anna Rita Bellu, Jan A.k.w. Kiel, Florian A Salomons, Ida J. Van Der KleiAbstract:Selective degradation of peroxisomes (macropexophagy) in Hansenula polymorpha involves the sequestration of individual organelles to be degraded by membranes prior to the fusion of this compartment with the vacuole and subsequent degradation of the whole organelle by vacuolar hydrolases. Here we show that Pex3p, a peroxisomal membrane protein essential for peroxisome biogenesis, escapes this autophagic process. Upon induction of macropexophagy, Pex3p is removed from the organelle tagged for degradation prior to its sequestration. Our data indicate that Pex3p degradation is essential to allow the initiation of the organellar degradation process. Also, in a specific peroxisome degradation-deficient (pdd) mutant in which sequestration still occurs but the vacuolar fusion event is disturbed, the turnover of Pex3p is still observed. Taken together, our data suggest that degradation of Pex3p is part of the initial degradation machinery of individual peroxisomes.