Chaperone proteins typically recognize a number of different

Chaperone proteins typically recognize a number of different unfolded protein substrates. Similarly, there are certain Unfoldases that recognize misfolded proteins and attempt to unfold them, in order to allow them to refold correctly. What might be a commo protein targets (in other words, what is most likely common to the proteins recognized by either Chaperones or Unfoldases)? n mechanism by which Chaperones and Unfoldases recognize their different

Solution

Chaperones :

Molecular chaperones are a part of quality control system that helps in restoring proteoins that might have become misfolded after various forms of stress, including exposure to excessive heat. Thus, heat shock response increases the expression of Chaperones. They were originally identified as Heat shock proteins - Hsp60 & Hsp70.

Chaperones (both Hsp60 & Hsp70) bind substrate proteins mostly non specifically, and they cycle between binding and release of substrates in an ATP-dependent manner. Hsp70, a simple chaperone that prevents improper folding and aggregation whereas Hsp60 promotes proper folding.

Hsp70 works in the following process -

The process starts with binding of a substrate unfolded protein with DnaJ, a co-chaperone, which intearcts with the ATP-bound form of Hsp70. This is followed by hydrolysis of ATP, generating ADP and closing of Hsp70 binding pocket and dissociation of co-chaperone. Thus, substrate unfolded protein binds tightly with Hsp70. This is followed by binding of another protein GrpE to Hsp70 allowing conformational change of Hsp70 releasing ADP which is responsible for opening of Hsp70 binding pocket and the cycle continues. Example - DnaK-DnaJ-GrpE

Hsp60 works in the following process -

The similar process happens with Hsp60 as well, where the substrate unfolded protein binds to the open state of Hsp60, followed by binding of ATP which allows the proper folding of the substrate protein and ATP hydrolysis. The ATP hydrolysis allows a conformational change in Hsp60 allowing the diffusion of the folded protein.

Unfoldase :

Unfoldases also recognises the unfolded protein similar to chaperones. The only difference is that the unfoldases requires an adaptor protein. The adaptor protein recognises the unfolded substrate protein and allows it to bind to unfoldase in an ATP dependent manner followed by folding or degradation of substrate protein and recycling of adaptor protein with hydrolysis of ATP.

Thus, both chaperones and unfoldases work by binding and release of substrates in an ATP-dependent manner.

Reference :

1. Bukau, B; Horwich, A.L. The Hsp70 and Hsp60 Chaperone machines. Cell, 1992, 351-366