Hsp78, a Clp homologue within mitochondria, can substitute for chaperone functions of mt-hsp70.
Hsp78 is a Clp homologue within mitochondria of Saccharomyces cerevisiae. Deletion of HSP78 does not cause any detectable changes in wild type cells, but results in a petite phenotype in the ssc1-3 mutant strain carrying a temperature-sensitive allele of mt-hsp70. When overexpressed in the ssc1-3 mutant strain, hsp78 suppresses the defect in mitochondrial protein import under permissive conditions in vitro and interacts directly with newly imported polypeptide chains. As a molecular chaperone, hsp78 prevents the aggregation of misfolded proteins in the matrix of mitochondria under conditions of impaired mt-hsp70 function. However, unlike misfolded proteins associated with mt-hsp70, hsp78- bound polypeptides are not efficiently degraded by the ATP-dependent PIM1 protease. Thus, hsp78 can partially substitute for mt-hsp70 functions in the assembly of mitochondria and may be part of a salvage pathway if mt-hsp70 is limiting.[1]References
- Hsp78, a Clp homologue within mitochondria, can substitute for chaperone functions of mt-hsp70. Schmitt, M., Neupert, W., Langer, T. EMBO J. (1995) [Pubmed]
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