In the cell, as in vitro, the final conformation of a protein is determined by its amino-acid sequence. But whereas some isolated proteins can be denatured and refolded in vitro in the absence of other macromolecular cellular components, folding and assembly of polypeptides in vivo involves other proteins, many of which belong to families that have been highly conserved during evolution.

Protein folding in the cell.

HSP70; CHARACTERISTICS AND FUNCTION S 582 HSP70 Diversity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 582 Cytop lasmic HSP70 Genes and Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . .. 583 Cytoplasmic HSP70 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . 586 HSP70 in the Endoplasmic Reticulum . . . . .. . . ..... . . .... . . . . . . . . ... . 588 Mitochondrial and Chloroplast HSP70s . . . .. . .. . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 588 H SP60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590 Mitochondrial HSP60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590 Chloroplast Chaperonin 60 . . . . . . . .... . . . . . .. . . . ....... ........ . ......... . ....... . . . . .. . . . ...... 591 LMW HSPs . . . . . . . . " . . ... .... ,... ....... . . . ........ . ...... . ...... 593 The LMW HSP Gene Supeifamily . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . . . . . . . . 593 LMW HSP Structure . . . . . . . . . . . . . . . . . . . . . . . . . , .... , , 597 P lastid LMW HSPs . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . , ..... .... , 599 Endomembrane LMW HSPs . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . 601 LMW HSP Function . .. . . . .. . . . . . . .... . . . . . .... . . . .. . . . . . . . . . . . . . . . . . . . ... . . . . . . . .... . . . . . . . . . . . . 602 OTHER H SPs . . 604 HSP90 and HSPlJO. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 604 Ubiquitin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , ... ,......... 605 Additional Heat-Regulated Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . 606 RELEV ANCE OF HSPS TO PLANT G ROWTH AND DEVELOPMENT 607 Expression of HSPs in the Natural Environment . . .. . . . . . . . ..... . . . . . .. . . . . . . . . . . ....... .. . 607 HSP Expression During Development 608 Role of HSPs in Thermotolerance . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . 609 SUMMARY AND FUTURE PROSPECTS....... ....... ..... . .... .. . .. ....... ..... 611

The Roles of Heat Shock Proteins in Plants

In contrast to such “shocks” for which the genome is unprepared, are those a genome must face repeatedly, and for which it is prepared to respond in a programmed manner. Examples are the “heat shock” responses in eukaryotic organisms, and the “SOS” responses in bacteria. Each of these initiates a highly programmed sequence of events within the cell that serves to cushion the effects of the shock. Some sensing mechanism must be present in these instances to alert the cell to imminent danger, and to set in motion the orderly sequence of events that will mitigate this danger. The responses of genomes to unanticipated challenges are not so precisely programmed. Nevertheless, these are sensed, and the genome responds in a discernible but initially unforeseen manner. Barbara McClintock–Nobel lecture , 8 December 1983 These prophetic words by Barbara McClintock eloquently capture the essence of the heat shock response. At the time these words were written, it was known that all organisms shared a common response to physiological stress. Some of the genes encoding heat shock proteins had just been cloned and the basis of heat shock gene regulation was in the early stages of investigation. However, the function of the heat shock response and the role of heat shock proteins were still a mystery. This mystery slowly began to unravel, and by the 1980s, some information on the function of the heat shock proteins as proteases or unfolded polypeptide-binding proteins had already accumulated. These early stages of elucidation of the biochemical...

https://epub.ub.uni-muenchen.de/7685/1/7685.pdf

The Biology of heat shock proteins and molecular chaperones.

The 70-kilodalton family of heat shock proteins (Hsp 70) has been implicated in posttranslational protein assembly and translocation. Binding of cytosolic forms of Hsp 70 (Hsp 72,73) with nascent proteins in the normal cell was investigated and found to be transient and adenosine triphosphate (ATP)-dependent. Interaction of Hsp 72,73 with newly synthesized proteins appeared to occur cotranslationally, because nascent polypeptides released prematurely from polysomes in vivo can be isolated in a complex with Hsp 72,73. Moreover, isolation of polysomes from short-term [35S]Met-labeled cells (pulsed) revealed that Hsp 72,73 associated with nascent polypeptide chains. In cells experiencing stress, newly synthesized proteins coimmunoprecipitated with Hsp 72,73; however, in contrast to normal cells, interaction with Hsp 72,73 was not transient. A model consistent with these data suggests that under normal growth conditions, cytosolic Hsp 72,73 interact transiently with nascent polypeptides to facilitate proper folding, and that metabolic stress interferes with these events.

https://science.sciencemag.org/content/sci/248/4957/850.full.pdf

Interaction of Hsp 70 with newly synthesized proteins: implications for protein folding and assembly

Mitochondria import many hundreds of different proteins that are encoded by nuclear genes These proteins are targeted to the mitochondria, translocated through the mitochondrial membranes, and sorted to the different mitochondrial subcompartments Separate translocases in the mitochondrial outer membrane (TOM complex) and in the inner membrane (TIM complex) facilitate recognition of preproteins and transport across the two membranes Factors in the cytosol assist in targeting of preproteins Protein components in the matrix partake in energetically driving translocation in a reaction that depends on the membrane potential and matrix-ATP Molecular chaperones in the matrix exert multiple functions in translocation, sorting, folding, and assembly of newly imported proteins

Protein import into mitochondria.

Identification, characterization, and purification of two mammalian stress proteins present in mitochondria, grp 75, a member of the hsp 70 family and hsp 58, a homolog of the bacterial groEL protein.

C Chang

Papers

Identification, characterization, and purification of two mammalian stress proteins present in mitochondria, grp 75, a member of the hsp 70 family and hsp 58, a homolog of the bacterial groEL protein.