Many heat shock proteins function together in co-chaperone complexes, such as
Hsp70/
Hsp40 (bacterial
DnaK/
DnaJ) that along with
GrpE acts as an ATP-regulated shuttle complex for newly synthesized proteins. Many of these nascent peptides are delivered to
Hsp90-containing complexes, which play a critical role in the stabilization and activation of key signaling kinases and hormone receptors. The
Hsp60/
Hsp10 complex (bacterial
GroEL/
GroES) forms an alternative protein folding mechansism in the mitochondria. Small heat shock proteins including
Hsp27 and the
crystallins form large oligomeric complexes that function to prevent protein aggregation.