Stress is a complex phenomenon which alters normal physiological equilibrium or homeostasis of animals. It is revealed
by inability of animal to cope with its environment, a phenomenon that is often reflected in the failure to achieve genetic
potential for production traits. Cells increase the expression of several classes of proteins in response to environmental stresses
such as heat shock. Heat shock proteins (HSP) are a class of functionally related proteins involved in the folding and unfolding
of other proteins. Heat shock proteins are present in cells under normal conditions but their expression is increased when cells
are exposed to elevated temperatures or other stress. Heat shock proteins family consists of many proteins which are classified as
HSP110, HSP100, HSP90, HSP70, HSP60, HSP40, HSP10 and small HSP families. The principal heat-shock proteins that have
chaperone activity belong to five conserved classes: HSP33, HSP60, HSP70, HSP90, HSP100 and the small heat-shock proteins.
Some members of the HSP family are expressed at low to moderate levels in all organisms because of their essential role in
protein maintenance. These account for 1-2% of total protein in unstressed cells which increased to 4-6% of cellular proteins
when cells are exposed to heat stress. HSPs help in maintaining cellular homeostasis by three principal biochemical activities.-
1) Chaperonin activity 2) Regulation of cellular redox state 3) Regulation of protein turnover and they participate in numerous
functions including folding of newly synthesized proteins, transport of protein into cell compartment, disaggregation of protein
complexes and other functions.
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