Heat shock proteins (HSP) are a class of functionally related proteins involved in the folding and unfolding of other proteins. Their expression is increased when cells are exposed to elevated temperatures or other stress. This increase in expression is transcriptionally regulated. The dramatic upregulation of the heat shock proteins is a key part of the heat shock response and is induced primarily by heat shock factor (HSF). HSPs are found in virtually all living organisms, from bacteria to humans.
Heat-shock proteins are named according to their molecular weight. For example, Hsp60, Hsp70 and Hsp90 (the most widely-studied HSPs) refer to families of heat shock proteins on the order of 60, 70 and 90 kilodaltons in size, respectively. The small 8 kilodalton protein ubiquitin, which marks proteins for degradation, also has features of a heat shock protein.
It is known that rapid heat hardening can be elicited by a brief exposure of cells to sub-lethal high temperature, which in turn provides protection from subsequent and more severe temperature. In 1962, Ritossa reported that heat and the metabolic uncoupler dinitrophenol induced a characteristic pattern of puffing in the chromosomes of Drosophila. This discovery eventually led to the identification of the heat-shock proteins (HSP) or stress proteins whose expression these puffs represented. Increased synthesis of selected proteins in Drosophila cells following stresses such as heat shock was first reported in 1974.
Beginning in the mid-1980s, investigators recognized that many HSPs function as molecular chaperones and thus play a critical role in protein folding, intracellular trafficking of proteins, and coping with proteins denatured by heat and other stresses. Accordingly, the study of stress proteins has undergone explosive growth.
Heat-shock protein (HSP) can be utilized as a vaccine to cross-protect against multiple pathogenic species. Investigators from Pusan National University (South Korea) presented the findings of a study they performed to evaluate the bacterium Porphyromonas gingivalis heat-shock protein (HSP) 60 as a vaccine candidate to inhibit multiple bacteria-induced alveolar bone loss. Recombinant P. gingivalis HSP60 was produced and purified from P. gingivalis GroEL gene. Rats were immunized with P. gingivalis HSP60, and experimental alveolar bone loss was induced by infection with multiple periodontopathogenic bacteria.
There was a very strong inverse relationship between post-immune anti-P. gingivalis HSP immunoglobulin G levels and the amount of alveolar bone loss induced by either P. gingivalis or multiple bacterial infection (p = 0.007). Analysis of data from polymerase chain-reaction indicated that the vaccine successfully eradicated the multiple pathogenic species.
The researchers concluded that P. gingivalis HSP60 could potentially be developed as a vaccine to inhibit periodontal disease induced by multiple pathogenic bacteria.