Disease relevance of HSP60

• Protein folding in mitochondria is mediated by the chaperonin Hsp60, the homologue of E. coli GroEL [1].
• Prevention of protein denaturation under heat stress by the chaperonin Hsp60 [2].

High impact information on HSP60

• Our data argue against this model: import intermediates of cytochromes c1 and b2 were found only outside the inner membrane; maturation of these proteins was independent of the matrix-localized hsp60 chaperone; and dihydrofolate reductase linked to the presequence of either cytochrome was imported to the intermembrane space in the absence of ATP [3].
• Heatshock protein 60 (hsp60) in the matrix of mitochondria is essential for the folding and assembly of newly imported proteins [4].
• Hsp60 belongs to a class of structurally related chaperonins found in organelles of endosymbiotic origin and in the bacterial cytosol [4].
• The hsp60 protein isolated from the protozoan Tetrahymena thermophila is induced in response to heat stress and is a member of an immunologically conserved family represented in Escherichia coli and in mitochondria of plants and animals [5].
• In vitro, Hsp60 bound to DHFR in the course of thermal denaturation, preventing its aggregation, and mediated its adenosine triphosphate-dependent refolding at increased temperatures [2].

Biological context of HSP60

• The HSP60 gene maps to chromosome XII [6].
• The predicted HSP60 contains a mitochondrial target sequence and exhibits striking amino acid sequence similarity to its counterparts in bacteria, plants, and humans [7].
• We have cloned the Saccharomyces cerevisiae HSP60 gene from a lambda gt11 genomic library using monoclonal antibodies, have obtained its sequence, determined its transcription start point, and shown that it exists as a single copy [7].
• Heat shock protein HSP60 can alleviate the phenotype of mitochondrial RNA-deficient temperature-sensitive mna2 pet mutants [8].
• Both mna2-1 and mna2-2, the two available alleles of mna2, have conservative single amino acid substitutions in the HSP60 gene [8].

Anatomical context of HSP60

• HSP60 was found to be the genetic locus of the conditional-lethal mutation described by Cheng et al., which at non-permissive temperature is defective in the assembly of several different multisubunit complexes in mitochondria [5].
• The recombinant HSP60 was used to immunize BALB/c mice and was shown to induce proliferation of T cells isolated from lymph nodes of these animals [9].
• The mitochondrial heat shock protein 60 (Hsp60) has now been shown to form complexes with a variety of polypeptides in organelles exposed to heat stress [2].
• Hsp60 subunits are encoded by a nuclear gene and translated in the cytosol as precursors which are translocated into mitochondria and proteolytically processed [4].
• Electron and confocal microscopy revealed that hsp60 resided on the yeast cell wall in discrete clusters [10].

Associations of HSP60 with chemical compounds

• When dimeric ribulose-1,5-bisphosphate carboxylase (Rubisco) is denatured and allowed to bind to yeast cpn60, subsequent refolding of Rubisco is strictly dependent upon yeast cpn10 [11].
• Consistently, the iron chelator deferoxamine protected low Hsp60-expressing cells from both oxidant-induced death and protein oxidation [12].
• We constructed mutant strains in which the levels of Hsp60 protein, compared with wild-type cells, were four times greater, and the addition of doxycycline gradually reduces them to 20% of wild-type [12].
• As these enzymes release their iron ions under oxidative-stress conditions, the intracellular labile iron pool, monitored with calcein, was higher in cells with reduced Hsp60 levels [12].
• Common targets include stress resistance proteins (Hsp60 and Hsp70) and enzymes involved in glucose metabolism such as enolase, glyceraldehydes-3-P dehydrogenase, fructose-1,6-biphosphate aldolase, pyruvate decarboxylase, and alcohol dehydrogenase [13].

Physical interactions of HSP60

• In the presence of ADP, one molecule of hsp10 binds to hsp60 with an apparent Kd of 0.9 nM and a second molecule of hsp10 binds with a Kd of 24 nM [14].

Other interactions of HSP60

• Our results identify Hsp10 as an essential component of the mitochondrial protein folding apparatus, participating in various aspects of Hsp60 function [1].
• Depletion of Mrs5p in yeast cells causes accumulation of unprocessed precursors of the mitochondrial hsp60 protein and defects in all cytochrome complexes [15].
• The Tcm62p sequence is 17.3% identical to yeast hsp60, a molecular chaperone [16].
• One H. polymorpha 70 kDa protein was strongly induced during growth at elevated temperatures, whereas a second 70 kDa protein as well as a 60 kDa protein showed strong protein sequence homology to mitochondrial SSC1 and hsp60, respectively, from S. cerevisiae [17].
• Depletion of Mrs11p results in a phenotype similar to that observed in Mrs5p-depleted cells: accumulation of the precursor form of mitochondrial hsp60, inability to form spectrophotometrically detectable amounts of cytochromes and changes in the mitochondrial morphology [18].

Analytical, diagnostic and therapeutic context of HSP60

• mna2, which belongs to the class I temperature-sensitive pet mutants that lose mitochondrial (mt)RNA at restrictive temperature, was shown by complementation and sequence determination to correspond to the gene coding for HSP60 [8].
• HSP60 expression appeared to be regulated during form transition in Pb, as different levels of expression were detected in in vitro labeling of cells and northern blot analysis [19].
• In the presence of MgATP, yeast cpn60 and yeast cpn10 form a stable complex that can be isolated by gel filtration and that facilitates refolding of denatured Rubisco [11].
• By electron microscopy, these particles are ring-shaped and reminiscent of proteins in the Hsp60 and TF55/TCP families [20].
• Of the methods that we tested for monitoring the association of imported proteins with hsp60, only co-immunoprecipitation with specific anti-hsp60 antibodies proved to be reliable [21].

References