Disulfide bonds covalent

F. 6.7. A disulfide bond. Covalent disulfide bonds may be formed between two molecules of cysteine or between two cysteine residues in a protein. The disulfide compound is called cystine. The hydrogens of the cysteine sulfhydryl groups are removed during oxidation. 

Note A molecular dynamics sim u lation cannot overcome con -strain is imposed by covalent bonds, such as disulfide bonds and rings. Check that such constraints are acceptable. Search other possible structures in separate simulations. 

Size Isomers. In solution, hGH is a mixture of monomer, dimer, and higher molecular weight oligomers. Furthermore, there are aggregated forms of hGH found in both the pituitary and in the circulation (16,17). The dimeric forms of hGH have been the most carefully studied and there appear to be at least three distinct types of dimer a disulfide dimer connected through interchain disulfide bonds (8) a covalent or irreversible dimer that is detected on sodium dodecylsulfate- (SDS-)polyacrylamide gels (see Electroseparations, Electrophoresis) and is not a disulfide dimer (19,20) and a noncovalent dimer which is easily dissociated into monomeric hGH by treatment with agents that dismpt hydrophobic interactions in proteins (21). In addition, hGH forms a dimeric complex with ( 2). Scatchard analysis has revealed that two ions associate per hGH dimer in a cooperative... 

Insulin is composed of two peptide chains covalently linked by disulfide bonds (Figures 5.17 and 6.35). This monomer of insulin is the active form that binds to receptors in target cells. However, in solution, insulin spontaneously forms dimers, which themselves aggregate to form hexamers. The surface of the insulin molecule that self-associates to form hexamers is also the surface that binds to insulin receptors in target cells. Thus, hexamers of insulin are inactive. 

Clostridial neurotoxins are bacterial protein toxins that consist of a heavy and a light chain connected by a disulfide bond and non-covalent interactions. They... 

In 2000, the first example of ELP diblock copolymers for reversible stimulus-responsive self-assembly of nanoparticles was reported and their potential use in controlled delivery and release was suggested [87]. Later, these type of diblock copolypeptides were also covalently crossUnked through disulfide bond formation after self-assembly into micellar nanoparticles. In addition, the encapsulation of l-anilinonaphthalene-8-sulfonic acid, a hydrophobic fluorescent dye that fluoresces in hydrophobic enviromnent, was used to investigate the capacity of the micelle for hydrophobic drugs [88]. Fujita et al. replaced the hydrophilic ELP block by a polyaspartic acid chain (D ). They created a set of block copolymers with varying... 

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. 

Figure 9-6. Selective proteolysis and associated conformational changes form the active site of chymotrypsin, which includes the Aspl 02-His57-Ser195 catalytic triad. Successive proteolysis forms prochymotrypsin (pro-CT), Jt-chymotrypsin (jt-CT),and ultimately a-chymotrypsin (a-CT), an active protease whose three peptides remain associated by covalent inter-chain disulfide bonds.

Fibrinogen (factor I, 340 kDa see Figures 51-1 and 51-4 and Tables 51-1 and 51-2) is a soluble plasma glycoprotein that consists of three nonidentical pairs of polypeptide chains (Aa,Bpy)2 covalently linked by disulfide bonds. The B(3 and y chains contain asparagine-linked complex oligosaccharides. All three... 

Most poly(HA) depolymerases are inhibited by reducing agents, e.g., dithio-erythritol (DTT), which indicates the presence of essential disulfide bonds, and by serine hydrolase inhibitors such as diisopropyl-fluoryl phosphate (DFP) or acylsulfonyl derivates. The latter compounds covalently bind to the active site serine of serine hydrolases and irreversibly inhibit enzyme activity [48]. 

Fig. 16.1 Sodium channel structure. Schematic representation of the sodium channel subunits, a, ySl and / 2. (A) The a-subunit consists of four homologous intracelIularly linked domains (I—IV) each consisting of six connected segments (1-6). The segment 4 of each of the domains acts as the voltage sensor, physically moving out in response to depolarization resulting in activation of the sodium channel. The channel is inactivated rapidly by the linker region between III and IV docking on to the acceptor site formed by the cytoplasmic ends of S5 and S6 of domain IV. The / -subunits have a common structure, with the / 1 non-covalently bound, and f 2 linked by disulfide bonds to the a-channel...

The second mode of toxicity is postulated to involve the direct interaction of the epidithiodiketopiperazine motif with target proteins, forming mixed disulfides with cysteine residues in various proteins. Gliotoxin, for example, has been demonstrated to form a 1 1 covalent complex with alcohol dehydrogenase [13b, 17]. Epidithiodi-ketopiperazines can also catalyze the formation of disulfide bonds between proxi-mally located cysteine residues in proteins such as in creatine kinase [18]. Recently, epidithiodiketopiperazines have also been implicated in a zinc ejection mechanism, whereby the epidisulfide can shuffle disulfide bonds in the CHI domain of proteins, coordinate to the zinc atoms that are essential to the tertiary structure of that domain, and remove the metal cation [12d, 19],... 

Figure 6.3 Mts-Atf-Biotin can be used to label bait proteins at available thiol groups using the MTS group, which forms a disulfide linkage after reaction. The modified protein then is allowed to interact with a protein sample and photoactivated with UV light to cause a covalent crosslink with any interacting proteins. Cleavage of the disulfide bond effectively transfers the biotin label to the unknown interacting protein.

Martin, F.J., Hubbell, W., and Papahyadjopoulos, D. (1981) Immunospecific targeting of liposomes to cells a novel and efficient method for covalent attachment of Fab fragments via disulfide bonds. Biochemistry 20, 4229-4238. 

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