An overview on the small heat shock proteins

Abstract

In the last 25 years, a huge amount of literature has been accumulated describing the cell's response to different kinds of environmental stress conditions, such as high temperatures, altered pH, exposure of the cell to toxins, starvation, oxygen, and water deprivation, among others. Heat shock proteins (HSPs) are one of the main expressed products of the cell in response to stresses. HSPs can be classified into six structurally conserved classes according to their molecular weight namely, HSP100, HSP90, HSP70, HSP60, small heat shock proteins (sHSPs) and ubiquitin (8.5 kDa). In eukaryotes, different heat shock genes are expressed uncoordinatedly, whereas in prokaryote, heat shock genes form a regulon and appear simultaneously. sHSPs are associated with nuclei, cytoskeleton and membranes. They bind partially to denatured proteins, preventing irreversible protein aggregation during stress. In animals, only one sHSP gene has been located in yeast cells, ten in mammalian, two in birds and four genes have been found in Drosophila. However, in plants more than 20 sHSPs have been reported and they can be divided into 6 classes, of which, 3 classes (CI, CII and CIII) are in the cytosole or in the nucleus and the other three (CIV, CV and CVI) in the plastids, endoplasmic reticulum and mitochondria. Mitochondrial and chloroplast sHSPs protect electron transport chain. During development in animals, sHSP genes are normally regulated at late neurula and early tailbud stage and in plants during pollen development, seed maturation, seed imbibition and germination. Transcriptional regulation of sHSPs depends on particular activation of heat shock factors (HSF) which recognize the highly conserved heat-shock elements (HSEs). After the heat stress has been released, the sHSPs are quite stable, suggesting that sHSPs may be important for recovery as well.

Switching between Heat Shock Proteins and Cold Inducible Proteins under Temperature Fluctuation in Solanum tuberosum L. Cultivars in In Vivo Condition

“…Further suggesting the translation of transcribed sHSPs mRNA's formed during heat stress as the plants gradually gain heat returning to normal temperature during recovery. This confirms the involvement of sHSPs in recovery (Yeh-Jin et al 2004), reviewed in (Efeogleu, 2009Mahmood et al 2010). The absence of polymorphism in cultivars protein profiles during recovery signifies convergence in the mechanism adopted by S. tuberosum L. to revive, entirely mediated by sHSPs and HKPs.…”

Tomato plant response to heat stress: a focus on candidate genes for yield-related traits

“…The Hsp60 family, also called chaperonins, helps in protein folding and subunit assembly. Despite the functional characterization of plant chaperonins is limited, they are important in assisting plastid proteins like Rubisco (Mahmood et al, 2010). Eighteen genes belonging to this family were found from Fragkostefanakis et al (2015) (Supplementary Table 2) as orthologues of those reported for Arabidopsis thaliana.…”

Improving thermo-tolerance of Saccharomyces cerevisiae by precise regulation of the expression of small HSP

“…13 HSP100 specically induce the breakdown of protein aggregates, HSP90 assists in the folding of specic target proteins, HSP70 aids in the proper folding of newly synthesized proteins, and sHSP proteins prevent the irreversible formation of protein aggregates. 13 HSPs are widely regarded as the most closely related functional molecules to heat resistance in cells. 14 When organisms are subjected to heat stress, the expression level of heat shock protein mRNA can increase by 10-100 times compared to non-stress conditions.…”

“…They can be classied into ve major classes: HSP100, HSP90, HSP70, HSP60, and small heat shock protein (sHSP) families. 13 HSP100 specically induce the breakdown of protein aggregates, HSP90 assists in the folding of specic target proteins, HSP70 aids in the proper folding of newly synthesized proteins, and sHSP proteins prevent the irreversible formation of protein aggregates. 13 HSPs are widely regarded as the most closely related functional molecules to heat resistance in cells.…”