![]() ![]() ![]() The 60 kDa chaperones form large oligomeric rings, and are also referred to as the chaperonins. This review focuses on Hsp60 class of molecular chaperones, highlighting Hsp60 with atypical structure and function. ![]() Much of our understanding on the mechanisms of chaperone-assisted protein folding has been derived from work on Hsp60 and Hsp70 families of chaperones. This type of classification holds true with few exceptions ( Richter et al., 2010 Kim et al., 2013). The chaperones are also classified based on their mode of action into: (a) Foldases, Chaperones that assist refolding of unfolded proteins by using ATP, e.g., Hsp70 and Hsp60, (b) Holdases, Chaperones that bind folding intermediates and prevent aggregation, e.g., sHsp and Hsp40, and (c) Disaggregases, Chaperones which actively disaggregate the harmful protein aggregates, which might lead to their small fragments, e.g., members of AAA + ATPase superfamily and Hsp100. These proteins are classified according to their molecular weight into five major families: (a) Hsp100 family, (b) Hsp90 family, (c) Hsp70 family, (d) Hsp60 family, and (e) small heat shock protein family (sHsp) ( Bohen et al., 1995 Schirmer et al., 1996 Bukau and Horwich, 1998). Apart from heat shock, other stress condition such as carbon, nitrogen, or phosphate limiting conditions were also known to induce molecular chaperones. Proteins reported to have chaperone activity were initially discovered as those overexpressed during heat shock and hence were named as the heat shock proteins (Hsp). Molecular chaperones comprise of a wide range of proteins playing key roles in cellular homeostasis and are responsible for assisting in protein folding, assembly of multimeric proteins, translocation of proteins within and across cell, degradation of unwanted, or misfolded proteins during normal cellular processes and stabilization of proteins by preventing aggregation and assisting in refolding under stress conditions ( Lindquist, 1986 Lindquist and Craig, 1988). ![]()
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