Molecular chaperone function of mammalian Hsp70 and Hsp40--a review

Virtually all organisms respond to up-shifts in temperature (heat shock) by synthesizing a set of proteins called heat shock proteins (HSPs). The HSPs are induced not only by heat shock but also by various other environmental stresses. Induction of HSPs is regulated by the trans-acting heat shock factors (HSFs) and cis-acting heat shock element (HSE) present at the promoter region of each heat shock gene. Usually, HSPs are also expressed constitutively at normal growth temperatures and have basic and indispensable functions in the life cycle of proteins as molecular chaperones, as well as playing a role in protecting cells from the deleterious stresses. Molecular chaperones are able to inhibit the aggregation of partially denatured proteins and refold them using the energy of ATP. Recently, there are expectations for the use of molecular chaperones for the protection against and therapeutic treatment of inherited diseases caused by protein misfolding. In this review, the focus will be on the mammalian Hsp40, a homologue of bacterial DnaJ heat shock protein, and the beneficial functions of molecular chaperones.