Chaperone proteins chaperonins

Proteasomes are sfrikingly similar in architecture, though not in peptide sequences, to another particle found in both bacteria and eukaryotes a molecular "chaperone" or chaperonin. The chaperonins, of which there are several types, protect proteins while they fold or undergo franslocation within cells. 

In vivo, the correct assembly of proteins is guided by a family of cellular proteins termed molecular chaperones, e.g., heat shock protein (HSP), nuleoplasmins, and chaperonins. Chaperones bind to the intermediate that tends to aggregate, and either assembles the intermediate to the native state or renders the intermediate void of further reaction to form an aggregate. Normally, all proteins should fold without molecular chaperones. Proteins that tend to form aggregates, like those shown in the above mechanisms, bind to a chaperone to yield the native state. 

Proper folding of proteins is essential for biological activity. Describe the roles of molecular chaperones and chaperonins in the folding of proteins. 

Protein folding is the result of interactions among very weak chemical attractions. Proteins have evolved to fold in conditions present in the cells. In some cases, chaperone proteins are required to help other proteins to fold properly. The structural proteins actin and tubulin cannot fold without their specific chaperonins present (King et al., 2002). 

Today, molecular chaperones are divided into three principle classes, according to their mode of action (Table 1). The one class comprises the chaperonins or HsplOO protein family members. Chaperonins are oligomeric proteins, composed of two rings placed... 

Hsp70 hands off the protein to another class of chaperones known as Hsp60 or simply chaperonins. Chaperonins create a protected environment sometimes known as an Anfinsen cage because it creates an enclosed environment in which the protein segments spontaneously fold, free from aggregating with other proteins and somewhat free from aqueous influences. These are large proteins that are somewhat cylindrical in shape. Chaperonins are composed of two major units, or stacked rings. 

For many proteins, folding is facilitated by Hsp70 chaperones and by chaperonins. 

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