Stability-related structural unfolding

Despite this low thermodynamic stability the permanent existence of a single secondary amide peptide bond in cis conformation per 1000 amino acid residues is the minimal population that has to be considered for unfolded polypeptide chains. This cis peptide bond fluctuates across the polypeptide chain in relation to the sequence-specific propensity of a secondary amide peptide bond to adopt the cis conformation. As could be found in folded proteins, nonprolyl cis peptides are frequently located in the fS-region of a q>/y/ plot [22]. It was hypothesized that cis peptide bonds represent high-energy structures able to store potential energy for increasing chemical reactivity [23]. Interconversion rates for the reversible CTI of secondary amide peptide bonds typically lead to half times of about 1 s for dipeptides, which decreases about 4-fold when the peptide bond is positioned in the middle of a longer peptide chain. 

The above examples throw light on the problem of unfolding (problem 2) and the related problem of structural stability of a function of one variable. Although the function V x) = x3 is structurally unstable, one may hope that its modification having the form... 

Isaacs BS, Brew SA, Ingham KC (1989) Reversible unfolding of the gelatin-binding domain of fibronectin structural stability in relation to function. Biochemistry 28 842-855... 

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