[Structured proteins and proteins with internal disorder].

The point of view that a uniquely folded protein tertiary structure is required for the protein functioning has been prevailing in the literature quite recently. However of lately it has been found that many proteins in a cell have no such structure in an isolated state, though they have a well-defined function in physiological conditions. These proteins were named as proteins with natural or internal disorder. The portion of disordered regions in such proteins may vary from a sequence of several amino acids to a completely disordered sequence containing from tens to hundreds of amino acids. The main difference of these proteins from the structured (globular) ones is that they have no unique tertiary structure in an isolated state and acquire it after interaction with their partners. Their conformation in such a complex depends on the interacting partner and not only on their own amino acid sequence, which is specific for structured (globular) proteins. The problem of structural and functional relations in the structured proteins and proteins with internal disorder is discussed in this review. The complexity of the problem and its potential solutions are illustrated by the example of elongation factors EFlA.