HSP78 Encodes a Yeast Mitochondrial Heat Shock Protein in the Clp Family of ATP-Dependent Proteases

Abstract

The Saccharomyces cerevisiae nuclear gene for a 78-kDa mitochondrial heat shock protein (hsp78) was identified in a lambda gt11 expression library through immunological screening with an hsp78-specific monoclonal antibody. Sequencing of HSP78 revealed a long open reading frame capable of encoding an 811-amino-acid, 91.3-kDa basic protein with a putative mitochondrial leader sequence and two potential nucleotide-binding sites. Sequence comparisons revealed that hsp78 is a member of the highly conserved family of Clp proteins and is most closely related to the Escherichia coli ClpB protein, which is thought to be an ATPase subunit of an intracellular ATP-dependent protease. The steady-state levels of HSP78 transcripts and protein varied in response to both thermal stress and carbon source with an approximately 30-fold difference between repressed levels in cells growing fermentatively on glucose at 30 degrees C and derepressed levels in heat-shocked cells growing on a nonfermentable carbon source. The response to heat shock is consistent with the presence of a characteristic heat shock regulatory element in the 5'-flanking DNA. Submitochondrial fractionation showed that hsp78 is a soluble protein located in the mitochondrial matrix. Cells carrying disrupted copies of HSP78 lacked hsp78 but were not impaired in respiratory growth at normal and elevated temperatures or in the ability to survive and retain mitochondrial function after thermal stress. The absence of a strong mitochondrial phenotype in hsp78 mutants is comparable to the nonlethal phenotypes of mutations in other Clp genes in bacteria and yeast. HSP78 is the third gene, with SSC1 and HSP60, known to encode a yeast mitochondrial heat shock protein and the second gene, with HSP104, for a yeast ClpB homolog.

Metabolic and Chaperone Gene Loss Marks the Origin of Animals: Evidence for Hsp104 and Hsp78 Chaperones Sharing Mitochondrial Enzymes as Clients

“…5A). This is consistent with previous reports showing that hsp104 deletion strains are measurably thermosensitive [50][51][52] while hsp78 deletion strains have more subtle effects when heat stressed [24][25][26][53][54][55]. However, we found that the hsp78 hsp104 double mutant was significantly more sensitive than hsp104 single mutant (~10-fold difference, p = 0.0005) suggesting that Hsp78 contributes to induced thermotolerance in the absence of Hsp104, although it has no appreciable effect in its presence (Fig.…”

“…Together with an N terminal domain, the two NBDs form a three tier hexameric ring with a central pore through which misfolded, aggregated peptides are translocated prior to refolding [22,23]. Hsp78 localizes and functions in the mitochondria [24][25][26], while Hsp104 localizes to the cytoplasm and nucleus [27]. Because of Hsp104's role in amyloid/cross-β disaggregation in yeast [28], the reason for the loss of the highly-conserved gene HSP104 in animals has been a source of much speculation [29].…”

Correction: Role of the HaHOG1 MAP Kinase in Response of the Conifer Root and But Rot Pathogen (Heterobasidion annosum) to Osmotic and Oxidative Stress

“…Our results correlates with the GPD1 induction as it was described in S. cerevisiae 15 min after salt osmotic stress [32]. The HSP78 gene encodes a mitochondrial heat shock protein and the transcript was found up-regulated in heatshocked S. cerevisiae cells when grown in a non-fermentable carbon source [33]. It was found to be up regulated also in saline stress [30] and high hydrostatic pressure [34].…”

Hsp78-interaction proteome highlights chaperone role during protein aggregation in mitochondria under heat stress

“…In contrast, a study in yeast established a strong effect of elevated temperatures on mitochondrial morphology (12). Yeast cells contain two homologs of bacterial Hsp100 family chaperone ClpB, the cytosolic Hsp104 (13), and the mitochondrial Hsp78 (14). As ClpB family members are not present in higher eukaryotes (15), it has been proposed that other chaperones, in particular mtHsp70 together with its co-chaperone Tid1, may take over Hsp100 function in human mitochondria (16).…”