Acting at a Distance

Abstract

MOLECULAR BIOLOGY Unfolded proteins are dangerous to the cell; exposing hydrophobic amino acid side chains will promote nonspecific aggregation and interfere with intracellular processes. Chaperones are proteins that assist in the folding and unfolding of other proteins. They are found in all organisms, and among their number are the so-called heat shock proteins (Hsps), which combat heat-induced stress. In Escherichia coli , the heat shock transcription factor σ32 regulates heat-shock gene expression, and it is in turn regulated by Hsps: DnaK (the prokaryote equivalent of Hsp70) and the co-chaperone DnaJ. Rodriguez et al. show that DnaK and DnaJ bind independently to distinct domains of σ32 in its native, folded state. The DnaK binding site would normally be occluded on σ32 that is bound to RNA polymerase, suggesting that DnaJ binds σ32 first. The binding of DnaJ destabilizes σ32 at a site in the vicinity of the DnaK binding site, favoring the rapid binding of DnaK once σ32 is released from RNA polymerase. Hsp70 systems in general may act in a similar manner: promoting disassembly and folding of aggregated substrate proteins by altering their conformations from a distance. — GR Mol. Cell 32 , 347 (2008).