Proteins stability disulfide bond

Cysteine contains sulfur and can form disulfide bonds to stabilize the shape (tertiary structure) of proteins. Destroying disulfide bonds denatures proteins. 

The folding of proteins into their three-dimensional structure is essential for their biological function. For proteins that contain disulfide bonds, formation of these bonds is often an important step in the folding reaction. The presence of one or more disulfide bonds is crucial to the maintenance of the folded state of many secretory proteins. In contrast, cytosolic proteins form disulfide bonds only as part of their catalytic cycle, and are not stabilized by these bonds. 

Figure 2 Location of stabilizing disulfide bonds (schematic) in the two main fractions of wheat gluten proteins (a) gliadin and (b) glutenin. 

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. 

Matsumura, M., Signor, G., Matthews, B.W. Substantial increase of protein stability by multiple disulfide bonds. Nature 342 291-293, 1989. 

Some proteins contain covalent disulfide (S— S) bonds that link the sulfhydryl groups of cysteinyl residues. Formation of disulfide bonds involves oxidation of the cysteinyl sulfhydryl groups and requires oxygen. Intrapolypeptide disulfide bonds further enhance the stability of the folded conformation of a peptide, while interpolypeptide disulfide bonds stabilize the quaternary structure of certain oligomeric proteins. 

Disulfide bonds between and within polypeptides stabilize tertiary and quaternary structure. However, disulfide bond formation is nonspecific. Under oxidizing conditions, a given cysteine can form a disulfide bond with the —SH of any accessible cysteinyl residue. By catalyzing disulfide exchange, the rupture of an S— bond and its reformation with a different partner cysteine, protein disulfide isomerase facilitates the formation of disulfide bonds that stabilize their native conformation. 

Insulin, a small protein of molecular mass 6000 daltons, is composed of two chains designated A and B. There are no reduced cysteine residues in insulin, but it contains three essential disulfide bonds two that crosslink the A and B chains, and one internal to the A chain to stabilize the overall tertiary stmcture. These disulfide bonds are cleaved in the presence of excess AuX4, leaving A and B chains that have cysteine residues that have become oxidized to sulfonic adds [119]. With smaller amounts of AuX4, a single disulfide bond will be attacked to form sulfinic acid [119]. The reaction is second order for AuCU while AuBr4 reacts too quickly for accurate monitoring. 

The extrusion process frequently results in realignment of disulfide bonds and breakage of intramolecular bonds. Disulfide bonds stabilize the tertiary structure of protein and may limit protein imfolding during extrusion (Taylor et al., 2006). Flow and melt characteristics were improved when other proteins were extruded with disulfide reducing agents (Areas, 1992), which indicates that disulfide bonds adversely affect... 

Fournier and DePristo96 calculated bond energies in several small compounds containing disulfide bonds which are known to stabilize the tertiary structure of proteins. Bond dissociation energies are generally overestimated when LDA(SVWN) is used whereas the PW86/P86 functional brings them to within 5 kcal/mol of experimental values. 

Disulfide bond formation Helps stabilize conformation of some proteins... 

HSA is a 585 amino acid, 65.5 kDa polypeptide. It is one of the few plasma proteins that are unglycosylated. A prominent feature is the presence of 17 disulfide bonds, which help stabilize the molecule s three-dimensional structure. HSA is synthesized and secreted from the liver, and its gene is present on human chromosome number 4. 

Thermolysin is a single-chain protease composed of 316 amino acids its amino acid sequence and three-dimensional structure (Colman et at, 1972) have been determined. The native protein has no disulfide bonds, but does contain both Ca2+ and Zn2+, which strongly stabilize the structure. 

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