Disulfide bonds, reducible

To investigate the hypothesis that dissociation of disulfite bonds into subunits might be a reaction occurring during formation of texturized soy flour (2 ), two disulfide bond reducing agents (Na2SO3, and cysteine-HCl) were added to soy... 

Reduction of conformational entropy Crosslinking, such as that achieved by forming disulfide bonds, reduces conformational entropy according to Eq. (17.38). 

A study on the effects of bond reducing chemicals on viruses [16] investigated the susceptibility of vims inactivation to dithiothreitol (DTT), a disulfide bond reducing agent. DTT was found to inactivate VACV after a 3-h incubation at 37°C. The authors suggested that the lipoprotein envelope present around poxviruses accounted for VACV susceptibility to DTT. 

Disulfide Bonds - Bonds between cysteine residues in a protein help to stabilize it once it has folded. Bovine pancreatic trypsin inhibitor (BPTI), which has 3 disulfide bonds in its 58 amino acid sequence, is one of the stablest proteins known. When the bonds are in place, it can be denatured at lOO C only in very acid solutions. Removing one disulfide bond reduces its resistance to thermal denaturation considerably. Removing all of the disulfide bonds causes it to unfold at room temperature. If time is allowed for refolding and the disulfide bonds are reformed, virtually 100% of the original activity of BPTI can be recovered, indicating that the sequence of amino acids contains enough information to properly reestablish the folding of the polypeptide. 

Figure 7.1 Comparing protein conformations by direct comparison of deuterium uptake curves. Shown here are two heavy-chain peptides from the antistreptavidin lgC2 antibody. Dashed lines represent the antibody with interchain disulfide bonds reduced, and the solid lines represent the native antibody (control). Each data point Is an average of two replicate analyses with standard deviation showing as the error bars. Most error bars are smaller than the size of marker points and thus not visible. Exchange time is on a logarithmic scale...

Deitcher, R.W., Xiao, Y., O Connell, J.P., Femruidez, E.J. (2009) Protein instability during HIC Evidence of unfolding reversibility, and apparent adsorption strength of disulfide bond-reduced a-lactalbumin variants. Biotechnol Bioeng, 102 (5), 1416—1427. 

Disulfides. The introduction of disulfide bonds can have various effects on protein stability. In T4 lyso2yme, for example, the incorporation of some disulfides increases thermal stability others reduce stability (47—49). Stabili2ation is thought to result from reduction of the conformational entropy of the unfolded state, whereas in most cases the cause of destabili2ation is the introduction of dihedral angle stress. In natural proteins, placement of a disulfide bond at most positions within the polypeptide chain would result in unacceptable constraint of the a-carbon chain. 

Several mucolytics reduce the viscosity of mucus by cleaving the disulfide bonds that maintain the gel stmcture. AJ-Acet l-L-cysteine [616-91 -1] (19), introduced in 1963, and mesna [19677-45-5] (20), developed in Europe in the early 1970s (20,21), are effective compounds in this class. Whereas most mucolytics must be adrninistered by aerosol, carbocysteine [638-23-6] (21), which contains a derivatized sulfhydryl group, has shown activity by the oral route (22,23). However, carbocysteine does not reduce mucus viscosity, as does acetylcysteine, but appears to have a direct action on mucus glycoprotein production (24). 

Disulfide bonds in proteins are generally stable and nonreactive, acting like bolts in the structure. However, oxidized DsbA is less stable than the reduced form and its disulfide bond is very reactive. DsbA is thus a strong... 

FIGURE 5.18 Methods for cleavage of disulfide bonds in proteins, (a) Oxidative cleavage by reaction with performic acid, (b) Reductive cleavage with snlfliydryl compounds. Disulfide bridges can be broken by reduction of the S—S link with snlfliydryl agents such as 2-mercaptoethanol or dithiothreitol. Because reaction between the newly reduced —SH groups to re-establish disulfide bonds is a likelihood, S—S reduction must be followed by —SH modification (1) alkylation with iodoac-etate (ICH,COOH) or (2) modification with 3-bromopropylamine (Br— (CH,)3—NH,). 

Recombinant soluble TNF-RI-IgGl fusion protein Etanercept, Enbrel is a chimeric molecule consisting of the extracellular domain of the TNF receptor I (TNF-RI) and the Fc portion of human IgGl. Two Fc domains are bound to each other via disulfide bonds, thereby yielding dimers with two binding sites for the TNF trimer. Etanercept binds with high affinity to extracellular TNF and reduces TNF activity. Etanercept is not effective in Crohn s disease, possibly because it does not lead to destiuction of membrane TNF-a expressing cells. Indications and side effects are similar to those of Infliximab and Adalimumab. 

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