Disease relevance of HSP26

• Hence, Hsp26 plays an important role in pathways that defend cells against environmental stress and the types of protein misfolding seen in neurodegenerative disease [1].
• We conclude that the intracellular location of hsp26 in yeast depends upon the physiological state of the cell and not simply upon the presence or absence of heat stress [2].
• Here, matrix-assisted refolding was applied to refold a double cysteine variant of Hsp26, a small heat-shock protein from Saccharomyces cerevisiae which was insoluble after biosynthesis in E. coli BL21 (DE3) cells [3].

High impact information on HSP26

• Hsp26 is one of the major heat shock proteins of eukaryotic cells [4].
• A particular pattern of heat-shock gene expression was observed during ascospore development in Saccharomyces: heat-shock proteins hsp26 and hsp84 were strongly induced nor inducible by heat shock [5].
• TOP1-dependent repression operates even on HSP26 and SSA3, which have been shown previously to be transcriptionally induced in early stationary phase [6].
• In contrast to Hsp26, which functions predominantly at heat shock temperatures, Hsp42 is active as a chaperone under all conditions tested in vivo and in vitro [7].
• To determine whether changes in nucleosome topology accompany transcription, we introduced into yeast a multicopy plasmid bearing the gene coding for the heat shock protein HSP26 [8].

Biological context of HSP26

• Deletion or point mutations of the C-terminal basic region caused an inefficient heat shock response of genes containing noncanonical HSEs such as CUP1 and HSP26 [9].
• The two tRNA genes, coding for a tRNA(asp) and a tRNA(arg), and three of the ORFs, had been sequenced previously, i.e. HSP26, SEC18, and UBC4 [10].
• The small heat shock proteins, Hsp26 and Hsp42, also function in the recovery of misfolded proteins and prevent aggregation in vitro, but their in vivo roles in protein homeostasis remain elusive [1].
• Only the upregulation of Hsp26 was detected by both methods [11].
• Taken together, our findings suggest that the quaternary structure of Hsp26 is determined by two elements, (i) weak, regulatory interactions required to form the shell of 24 subunits and (ii) a strong and stable dimerization of the C-terminal domain [12].

Anatomical context of HSP26

• Polysome analysis revealed that the wild-type PYK1, ACT1 and HSP26 mRNAs are all translated efficiently during stationary phase, when the translational apparatus is relatively inert [13].
• We show here that the sHsp system in the cytosol of S. cerevisiae consists of two proteins, Hsp26 and Hsp42 [7].
• With several independent clone cells of transformants, the levels of luciferase activity and some hsps, such as hsp104, hsp90, hsp70 and hsp26, were examined [14].

Associations of HSP26 with chemical compounds

• Third, the antibiotic thiolutin, previously demonstrated to inhibit all three yeast RNA polymerases both in vivo and in vitro, increases the RNA levels of HSP82 5- to 10-fold, those of SSA4 greater than 25-fold, and those of HSP26 greater than 50-fold under conditions in which transcription of non-heat-shock genes is blocked [15].
• MET14, a gene important for sulfite formation, was overexpressed in wort, using the HSP26 promoter during the stationary phase [16].
• Using this method we demonstrate that UBI4, YDJ1 and HSP26 are essential for stress tolerance of yeast during ethanol production [17].
• Subsequently, we demonstrated that a deletion mutant of Hsp26 was sensitive to sorbic acid [11].
• When log-phase cells growing in glucose were heat shocked, hsp26 concentrated in nuclei and continued to concentrate in nuclei when these cells were returned to normal temperatures for recovery [2].

Physical interactions of HSP26

• Our recent genomic footprinting experiments demonstrate that HSF binds constitutively to perfect and imperfect heat shock elements (HSEs) in the HSP26 gene in yeast [18].

Regulatory relationships of HSP26

• Expression of HSP42 is regulated by a range of stress conditions similar to S. cerevisiae HSP26, with which Hsp42p shares most homology [19].
• The Saccharomyces cerevisiae small heat shock protein Hsp26 inhibits actin polymerisation [20].

Other interactions of HSP26

• However, HSP42 expression is more sensitive to increased salt concentration and to starvation and, in contrast to HSP26 is expressed in unstressed cells [19].
• However, we found that reduction or elimination of PKA activity strongly derepresses transcription of the small heat-shock genes HSP26 and HSP12, even in the absence of MSN2/4 [21].
• HSP12, HSP26 and HSP30 were highly expressed [16].
• The GAL6 deletion does not affect the expression of another inducible gene, HSP26 [22].
• Furthermore, in Western blots, we observed that sod mutants showed a different pattern of Hsp104p and Hsp26p expression also different from that in their control strain [23].

Analytical, diagnostic and therapeutic context of HSP26

• We used Northern blotting to analyze mRNA levels of three stress marker genes, HSP26, GPD1, and ENA1, and 10 genes in different metabolic subcategories [24].
• We show that the oligomeric state and the structure, as determined by size exclusion chromatography and electron microscopy, corresponds to that of the Hsp26 wild-type protein [25].
• The analysis of the purified protein by electron microscopy revealed near spherical particles with a diameter of 12.0 nm (n=57, standard deviation +/-1.6 nm), displaying a dispersion in size ranging from 9.2 to 16.1 nm, identical to Methanococcus jannaschii Hsp16.5 and in the range of the size estimated for yeast Hsp26, in a previous report [26].
• Cryo-electron microscopy of yeast Hsp26 reveals two distinct forms, each comprising 24 subunits arranged in a porous shell with tetrahedral symmetry [27].

References