Interaction of Hsp 70 with Newly Synthesized Proteins: Implications for Protein Folding and Assembly

Abstract

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.

GroEL‐Mediated protein folding

“…For example, in the eukaryotic cytosol, both genetic and biochemical evidence support interaction of Hsp70 class proteins with nascent polypeptide chains (Beckmann et al, 1990;Nelson et al. 1992;Frydman et al.…”

Conformational change of chaperone Hsc70 upon binding to a decapeptide: A circular dichroism study

“…A 70-kDa heat shock cognate protein (Hsc70), the clathrin uncoating ATPase, is a member of the Hsp70 family, found in both cytosolic and nuclear matrices and believed to be involved in the folding of nascent proteins (Beckmann et al, 1990). Unlike the members of the Hsp70 family, however, Hsc70 is a constitutive stress protein that functions in normal cellular physiology (Hightower, 1991).…”

Heat shock increases turnover of 90 kDa heat shock protein phosphate groups in HeLa cells

“…For Instance, hsp60 and proteins of the 11~~70 family are known to associate with polypeptldes and to catalyze folding and unfolding reactions in an ATP-dependent manner [6,7] …”

“…For Instance, hsp60 and proteins of the 11~~70 family are known to associate with polypeptldes and to catalyze folding and unfolding reactions in an ATP-dependent manner [6,7] Hsp90 associates with various protems such as, for Instance, actm [8], calmodulm [9], src-type protein kindscs [lo] and stelold hormone receptors [I 1,121 These complexes correspond to an actlvatlon step of these proteins, which involves conformation and/or location changes.…”