Oligomers, sHsps

IV. Dynamic Nature of the sHsp Oligomer A. Subunit Exchange... 

In total these data indicate that sHsp oligomers are in rapid equilibrium with a smaller subassembly, which is not seen under standard analytical conditions. A similar subunit exchange has been reported between dimers of the tetrameric bacterial chaperone SecB (Topping et al., 2001) and monomers of the dimeric ft P>2-cryslallin (Slingsby and... 

Fig. 5. Model for sHsp chaperone activity. The sHsp oligomer (T Hspl6.9 shown here) is in rapid equilibrium with a smaller species (possibly a dimer). Heat-denatured substrates bind hydrophobic sites exposed on the sHsp subunits to form soluble sHsp/substrate complexes, preventing formation of insoluble aggregates of denatured proteins. The sHsp/substrate complexes may also be in rapid equilibrium, and when dissociated, the denatured substrate can be picked up and refolded in an ATP-dependent fashion by the Hsp70 or DnaK (plus cochaperone) machinery. Note that sHsp/substrate complexes can also become larger and insoluble, and the fate of these latter complexes is unknown.

FlG. 6. sHsp/substrate complexes observed by size exclusion chromatography. PsHspl8.1 (1 fiM oligomer) mixed with 1 fj,M MDH (A), 1 /xM Luc (B), or no substrate (C) was either maintained at room temperature or heated at 45° C for 60 min (MDH or no substrate) or 22 min (Luc), then separated at room temperature by size exclusion chromatography. Traces show absorbance at 220 nm versus elution time. Elution position of size standards indicated at the top. For further details, see Lee et al. (1997). 

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