Protein folding.

The problem of protein folding is that how proteins acquire their native unique three-dimensional structure in the physiological milieu. To solve the problem, the following key questions should be answered: do proteins fold co- or post-translationally, i.e. during or after biosynthesis, what is the mechanism of protein folding, and what is the explanation for fast folding of proteins? The two first questions are discussed in the current review. The general lines are to show that the opinion, that proteins fold after they are synthesized is hardly substantiated and suitable for solving the problem of protein folding and why proteins should fold cotranslationally. A possible tentative model for the mechanism of protein folding is also suggested. To this end, a thorough analysis is made of the biosynthesis, delivery to the folding compartments, and the rates of the biosynthesis, translocation and folding of proteins. A cursory attention is assigned to the role of GroEL/ES-like chaperonins in protein folding.