Hsp Chaperone Activity

After the chaperone activity of both Hsp70 and GroE were described (see Bukau and Horwich, 1998 Gething and Sambrook, 1992 for review), it was but a short leap of faith to consider that other Hsps might 

Although a lack of ATP requirement for sHsp/substrate interactions has been observed in several studies (Haslbeck et al., 1999 Horwitz, 1992 Jakob et al., 1993 Lee et al., 1995 Lee and Vierling, 2000 Merck et al., 1993a), ATP effects have been reported by others, primarily in experiments with o -crystallin. Clark and colleagues (Muchowski and Clark, 

1998) found that 3.5-mM ATP enhanced, by twofold, citrate synthase reactivation after dilution from denaturant in the presence ofaB-crystallin. 

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). 

The flexible C-terminal tail of mammalian sHsps does not seem to be involved directly in substrate binding (Carver et al., 1994 Lindner et al., 2000). Many sHsps without flexible tails are very effective chaperones. However, the tail appears to confer additional solubility to those sHsps with this feature, and thus can contribute indirectly to chaperone activity (Carver and Lindner, 1998). 

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