Heat Shock Proteins

Heat shock proteins (HSPs) are a large family of proteins found in both prokaryotes and eukaryotes. These are induced when a cell undergoes various types of environmental stresses so also, called as “stress protein”. The DNA sequence that makes up this family of genes is highly conserved across species. It is a group of binding proteins with a molecular weight of about 10 to 150 kD. HSPs are present in all cell compartments and are called by molecular sizes like Hsp27, Hsp70, Hsp90 etc. This family of genes originally was named because of their expression after exposure to heat. The response of heat shock was first observed in the Drosophila buscii salivary gland chromosomes. These are essential for survival at both normal and elevated temperatures. Also, appear to play a critical role in the development of thermotolerance.

The main functions of the HSPs are the holding and folding of other intracellular proteins. The HSPs are thus classified among the molecular chaperones, a group of polypeptides that mediate intracellular protein quality control under both housekeeping and stressed situations.

Stress proteins play a critical role in the maintenance of normal cellular homeostasis. These proteins almost certainly have a pivotal role in cell cycle progression and cell death (apoptosis) and are involved in many disease processes like cardiovascular disease.

HSPs may be important factors in an organism's response to a variety of physiologically relevant conditions, such as exercise, hyperthermia, oxidative stress, metabolic challenge, and aging. During ageing and different human diseases, like neurodegenerative disorders, stroke, atherosclerosis or myocardial infarction, there is increased level of oxidative stress. HSPs seems to be against oxidative stress. For instance, HSPBs decreases the level of reactive oxygen species (ROS) and regulate intracellular redox homeostasis thereby, protect cytoskeleton which is a sensitive target for oxidative stress. Furthermore, as molecular chaperons they prevent aggregation and promote proteosomal degradation of the oxidized proteins.

These are used as the potential markers of cellular injury and also used for diagnostic and therapeutic purposes Expression of different HSPs are also increased in the heart after ischemia/reperfusion injury. Like heat shock, ischemia/reperfusion injury activates HSF1. The activation of HSF can be detected in minutes during global ischemia in heart. However, the post-ischemic reperfusion induced a more significant activation of HSF.

HSPs play a significant role in protecting cells from various stresses like heat, cold, ischemia or glucose or oxygen deprivation. HSPs expression also enhances the antioxidant cell defence system under heat stress. HSPs also used as a biomarker for measure the level of heat stress in domestic animals as well as identification of thermotolerant animals under tropical climate. They are not only protecting the cells from different stresses but also involve in different cellular mechanism. Mechanism of HSPs yet to be revealed which assumed to play important role in diseases condition and other cellular mechanism.