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Mitochondrial enzymes are protected from stress-induced aggregation by mitochondrial chaperones and the Pim1/LON protease.

Bender T, Lewrenz I, Franken S, Baitzel C, Voos W - Mol. Biol. Cell (2011)

Bottom Line: To determine the effects of protein aggregation on the functional integrity of mitochondria, we set out to identify aggregation-prone endogenous mitochondrial proteins.Using specific chaperone mutant strains, we showed a protective effect of the mitochondrial Hsp70 and Hsp60 chaperone systems.Moreover, accumulation of aggregated polypeptides was strongly decreased by the AAA-protease Pim1/LON.

View Article: PubMed Central - PubMed

Affiliation: Institut für Biochemie und Molekularbiologie (IBMB), Universität Bonn, Nussallee 11, D-53115 Bonn, Germany.

ABSTRACT
Proteins in a natural environment are constantly challenged by stress conditions, causing their destabilization, unfolding, and, ultimately, aggregation. Protein aggregation has been associated with a wide variety of pathological conditions, especially neurodegenerative disorders, stressing the importance of adequate cellular protein quality control measures to counteract aggregate formation. To secure protein homeostasis, mitochondria contain an elaborate protein quality control system, consisting of chaperones and ATP-dependent proteases. To determine the effects of protein aggregation on the functional integrity of mitochondria, we set out to identify aggregation-prone endogenous mitochondrial proteins. We could show that major metabolic pathways in mitochondria were affected by the aggregation of key enzyme components, which were largely inactivated after heat stress. Furthermore, treatment with elevated levels of reactive oxygen species strongly influenced the aggregation behavior, in particular in combination with elevated temperatures. Using specific chaperone mutant strains, we showed a protective effect of the mitochondrial Hsp70 and Hsp60 chaperone systems. Moreover, accumulation of aggregated polypeptides was strongly decreased by the AAA-protease Pim1/LON. We therefore propose that the proteolytic breakdown of aggregation-prone polypeptides represents a major protective strategy to prevent the in vivo formation of aggregates in mitochondria.

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Protection from aggregation by other quality control components. (A, B) Isolated mitochondria from wild-type (WT) and deletion mutants hsp78Δ (A) or pim1Δ (B, upper panels) or from yeast overexpressing Pim1 from a plasmid (B, lower panels) were analyzed in the aggregation assay. Values shown are means ± SEM of the ratio of protein amount in the pellet compared with total mitochondrial lysate.
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Figure 6: Protection from aggregation by other quality control components. (A, B) Isolated mitochondria from wild-type (WT) and deletion mutants hsp78Δ (A) or pim1Δ (B, upper panels) or from yeast overexpressing Pim1 from a plasmid (B, lower panels) were analyzed in the aggregation assay. Values shown are means ± SEM of the ratio of protein amount in the pellet compared with total mitochondrial lysate.

Mentions: The Hsp100/Clp-like chaperone Hsp78 and its bacterial relative ClpB have been implicated in the recovery of proteins from aggregates (Goloubinoff et al., 1999; Krzewska et al., 2001). We also used mitochondria lacking Hsp78 in our assay to test whether the potential disaggregation activity of Hsp78 has a general protective effect on our reporter proteins. However, no significant differences in aggregation levels of Aco1 and Ilv2 could be observed between wild-type and hsp78Δ mitochondria at all temperatures tested (Figure 6A). We conclude that, under heat stress, the overall benefit of the Hsp78 activity concerning the protection of the model substrates from aggregation was negligible.


Mitochondrial enzymes are protected from stress-induced aggregation by mitochondrial chaperones and the Pim1/LON protease.

Bender T, Lewrenz I, Franken S, Baitzel C, Voos W - Mol. Biol. Cell (2011)

Protection from aggregation by other quality control components. (A, B) Isolated mitochondria from wild-type (WT) and deletion mutants hsp78Δ (A) or pim1Δ (B, upper panels) or from yeast overexpressing Pim1 from a plasmid (B, lower panels) were analyzed in the aggregation assay. Values shown are means ± SEM of the ratio of protein amount in the pellet compared with total mitochondrial lysate.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3046053&req=5

Figure 6: Protection from aggregation by other quality control components. (A, B) Isolated mitochondria from wild-type (WT) and deletion mutants hsp78Δ (A) or pim1Δ (B, upper panels) or from yeast overexpressing Pim1 from a plasmid (B, lower panels) were analyzed in the aggregation assay. Values shown are means ± SEM of the ratio of protein amount in the pellet compared with total mitochondrial lysate.
Mentions: The Hsp100/Clp-like chaperone Hsp78 and its bacterial relative ClpB have been implicated in the recovery of proteins from aggregates (Goloubinoff et al., 1999; Krzewska et al., 2001). We also used mitochondria lacking Hsp78 in our assay to test whether the potential disaggregation activity of Hsp78 has a general protective effect on our reporter proteins. However, no significant differences in aggregation levels of Aco1 and Ilv2 could be observed between wild-type and hsp78Δ mitochondria at all temperatures tested (Figure 6A). We conclude that, under heat stress, the overall benefit of the Hsp78 activity concerning the protection of the model substrates from aggregation was negligible.

Bottom Line: To determine the effects of protein aggregation on the functional integrity of mitochondria, we set out to identify aggregation-prone endogenous mitochondrial proteins.Using specific chaperone mutant strains, we showed a protective effect of the mitochondrial Hsp70 and Hsp60 chaperone systems.Moreover, accumulation of aggregated polypeptides was strongly decreased by the AAA-protease Pim1/LON.

View Article: PubMed Central - PubMed

Affiliation: Institut für Biochemie und Molekularbiologie (IBMB), Universität Bonn, Nussallee 11, D-53115 Bonn, Germany.

ABSTRACT
Proteins in a natural environment are constantly challenged by stress conditions, causing their destabilization, unfolding, and, ultimately, aggregation. Protein aggregation has been associated with a wide variety of pathological conditions, especially neurodegenerative disorders, stressing the importance of adequate cellular protein quality control measures to counteract aggregate formation. To secure protein homeostasis, mitochondria contain an elaborate protein quality control system, consisting of chaperones and ATP-dependent proteases. To determine the effects of protein aggregation on the functional integrity of mitochondria, we set out to identify aggregation-prone endogenous mitochondrial proteins. We could show that major metabolic pathways in mitochondria were affected by the aggregation of key enzyme components, which were largely inactivated after heat stress. Furthermore, treatment with elevated levels of reactive oxygen species strongly influenced the aggregation behavior, in particular in combination with elevated temperatures. Using specific chaperone mutant strains, we showed a protective effect of the mitochondrial Hsp70 and Hsp60 chaperone systems. Moreover, accumulation of aggregated polypeptides was strongly decreased by the AAA-protease Pim1/LON. We therefore propose that the proteolytic breakdown of aggregation-prone polypeptides represents a major protective strategy to prevent the in vivo formation of aggregates in mitochondria.

Show MeSH
Related in: MedlinePlus