Wrapping Translates into Protein Architecture

SCOP family a Sequence identity A Y-5AX AX Ay Homolog 1 Homolog 2 

The baseline structural deficiency Y = 20 represents the maximum of a tight distribution (standard deviation a = 2.25) of T-values for the structural deficiency of soluble proteins with no disulfide bridges. This baseline T-value implies that soluble proteins are not perfectly packed and maintain at least 20% of unburied backbone hydrogen bonds. Since such structural deficiencies locally promote backbone hydration, they belong to an intermediate region between order and disorder and hence represent markers of structural flexibility. Thus, because of its universality, the Y = 20 constant may be interpreted as the baseline flexibility needed for protein function. 

In this chapter, dehydrons were characterized as structural deficiencies. These deficiencies are of a special kind They are promoters of backbone hydration [4] and hence destabilizers of the native structure. On the other hand, disulfide bonds pre-formed in the denatured state reduce the structure-destabilizing conformational entropy cost associated with the folding process [12], hence stabilizing the native 

This relation is hence likely to assist the molecular engineering of soluble proteins. Furthermore, since disulfide bridges can be formed or dismantled in accord with redox environmental conditions, the relation presented is likely to enable the type of design fine-tuning that may be required for an environmental modulation of the protein function. 

As the dehydron/disulfide organizational principle is established and shown to hold for soluble proteins, we cannot fail to notice that it also introduces a new set of problems stemming from a basic question What is in physical terms the fate of a soluble protein whose structure significantly violates the architectural constraints defined by the balance equation This issue will be explored in Chap. 5. 

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