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Encyclopedia > Disulfide bond

In chemistry, a disulfide bond is a single covalent bond derived from the coupling of thiol groups. The linkage is also called an SS-bond or disulfide bridge. The overall connectivity is therefore C-S-S-C. The terminology is almost exclusively used in biochemistry and bioorganic chemistry. Formally the connection is called a persulfide, in analogy to a peroxide (R-O-O-R), but this terminology is rare. Chemistry (from Greek Ï‡Î·Î¼ÎµÎ¯Î± khemeia[1] meaning alchemy) is the science of matter at the atomic to molecular scale, dealing primarily with collections of atoms, such as molecules, crystals, and metals. ... Covalently bonded hydrogen and carbon in a molecule of methane. ... In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom (-SH). ...

Three sulfur atoms singly bonded in a sequence are sometimes called a trisulfide bond, although there are in fact two S-S bonds. Disulfide bonds are usually formed from the oxidation of sulfhydryl (-SH) groups, as depicted formally in Figure 1. The most fundamental reactions in chemistry are the redox processes. ... In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom (-SH). ...

Figure 1: Formal depiction of disulfide bond formation as an oxidation.

## Contents

Image File history File links Download high resolution version (3071x945, 15 KB) Summary Self-made in ChemDraw by Ben 23:28, 21 February 2006 (UTC) Licensing I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU... Image File history File links Download high resolution version (3071x945, 15 KB) Summary Self-made in ChemDraw by Ben 23:28, 21 February 2006 (UTC) Licensing I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU...

## Disulfide bonds in proteins

Disulfide bonds play an important role in the folding and stability of some proteins, usually proteins secreted to the extracellular medium. Since most cellular compartments are a reducing environment, disulfide bonds are generally unstable in the cytosol (with some exceptions noted below). A reducing environment is one chacterized by little or no free oxygen (dissolved or as a gas). ... ÃƒThe cytosol (as opposed fatty cytoplasm, which also includes the organelles) is the internal fluid of the cell, and a large part of cell metabolism occurs here. ...

Figure 2: Cystine is composed of two cysteines linked by a disulfide bond (shown here in its neutral form).

Disulfide bonds in proteins are formed between the thiol groups of cysteine residues. The other sulfur-containing amino acid, methionine, cannot form disulfide bonds. A disulfide bond is typically denoted by hyphenating the abbreviations for cysteine, e.g., the "Cys26-Cys84 disulfide bond", or the "26-84 disulfide bond", or most simply as "C26-C84" where the disulfide bond is understood and does not need to be mentioned. The prototype of a protein disulfide bond is the two-amino-acid peptide, cystine, which is composed of two cysteine amino acids joined by a disulfide bond (shown in Figure 2 in its unionized form). The structure of a disulfide bond can be described by its χss dihedral angle between the CβSγSγCβ atoms, which is usually close to ±90°. Image File history File links Download high resolution version (1897x2415, 42 KB) Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cysteine Cystine ... Image File history File links Download high resolution version (1897x2415, 42 KB) Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cysteine Cystine ... Chemical structure of cystine formed from L-cysteine (under biological conditions) 3D representation of cystine with the disulfide bond shown in yellow Cystine is a conditionally non-essential crystalline, sulfur-containing amino acid. ... Cysteine is a naturally occurring amino acid which has a thiol group and is found in most proteins, though only in small quantities. ... In organic chemistry, a thiol is a compound that contains the functional group composed of a sulfur atom and a hydrogen atom (-SH). ... Cysteine is a naturally occurring amino acid which has a thiol group and is found in most proteins, though only in small quantities. ... Methionine (Met, M. C5H11NO2S) is an essential nonpolar amino acid, and a lipotropic. ... Chemical structure of cystine formed from L-cysteine (under biological conditions) 3D representation of cystine with the disulfide bond shown in yellow Cystine is a conditionally non-essential crystalline, sulfur-containing amino acid. ... Cysteine is a naturally occurring amino acid which has a thiol group and is found in most proteins, though only in small quantities. ... In Aerospace engineering, the dihedral is the angle that the two wings make with each other. ...

The disulfide bond stabilizes the folded form of a protein in several ways: 1) It holds two portions of the protein together, biasing the protein towards the folded topology. Expressed differently, the disulfide bond destabilizes the unfolded form of the protein by lowering its entropy. 2) The disulfide bond may form the nucleus of a hydrophobic core of the folded protein, i.e., local hydrophobic residues may condense around the disulfide bond and onto each other through hydrophobic interactions. 3) Related to #1 and #2, the disulfide bond link two segments of the protein chain, the disulfide bond increases the effective local concentration of protein residues and lowers the effective local concentration of water molecules. Since water molecules attack amide-amide hydrogen bonds and break up secondary structure, a disulfide bond stabilizes secondary structure in its vicinity. For example, researchers have identified several pairs of peptides that are unstructured in isolation, but adopt stable secondary and tertiary structure upon forming a disulfide bond between them. Loop entropy is the entropy lost upon bringing together two residues of a polymer within a prescribed distance. ... The hydrophobic effect is the property that nonpolar molecules like to self-associate in the presence of aqueous solution. ... Hydrophobe (from the Greek (hydros) water and (phobos) fear) in chemistry refers to the physical property of a molecule that is repelled by water. ... Snapshot from a simulation of liquid water. ... A representation of the 3D structure of the Myoglobin protein. ...

Disulfide bonds in proteins are formed by thiol-disulfide exchange reactions. A disulfide species is a particular pairing of cysteines in a disulfide-bonded protein and is usually depicted by listing the disulfide bonds in parentheses, e.g., the "(26-84, 58-110) disulfide species". A disulfide ensemble is a grouping of all disulfide species with the same number of disulfide bonds, and is usually denoted as the 1S ensemble, the 2S ensemble, etc. for disulfide species having one, two, etc. disulfide bonds. Thus, the (26-84) disulfide species belongs to the 1S ensemble, whereas the (26-84, 58-110) species belongs to the 2S ensemble. The single species with no disulfide bonds is usually denoted as R for "fully reduced". Under typical conditions, disulfide reshuffling is much faster than the formation of new disulfide bonds or their reduction; hence, the disulfide species within an ensemble equilibrate more quickly than between ensembles. Thiol-disulfide exchange is a chemical reaction in which a thiolate group attacks a sulfur atom of a disulfide bond -S-S-. The original disulfide bond is broken, and its other sulfur atom (green atom in Figure 1) is released as a new thiolate, carrying away the negative charge. ... Thiol-disulfide exchange is a chemical reaction in which a thiolate group attacks a sulfur atom of a disulfide bond -S-S-. The original disulfide bond is broken, and its other sulfur atom (green atom in Figure 1) is released as a new thiolate, carrying away the negative charge. ...

The native form of a protein is usually a single disulfide species, although some proteins may cycle between a few disulfide states as part of their function, e.g., thioredoxin. In proteins with more than two cysteines, non-native disulfide species may be formed, which are almost always unfolded. As the number of cysteines increases, the number of nonnative species increases factorially. The number of ways of forming p disulfide bonds from n cysteine residues is given by the formula Thioredoxins are small proteins involved in thiol-redox processes. ...

$frac{n!}{p! (n - 2p)! 2^{p}}$

For example, an eight-cysteine protein such as ribonuclease A has 105 different four-disulfide species, only one of which is the native disulfide species. Isomerases have been identified that catalyze the interconversion of disulfide species, accelerating the formation of the native disulfide species. Structure of RNase A Ribonuclease A (RNase A) is an endonuclease that cleaves single-stranded RNA. Bovine pancreatic RNase A is one of the classic model systems of protein science. ...

Disulfide species that have only native disulfide bonds (but not all of them) are denoted by des followed by the lacking native disulfide bond(s) in square brackets. For example, the des[40-95] disulfide species has all the native disulfide bonds except that between cysteines 40 and 95. Disulfide species that lack one native disulfide bond are frequently folded, particularly if the missing disulfide bond is exposed to solvent in the folded, native protein.

Toxic heavy metals such as lead and mercury are able to attack disulfide bonds, forming extremely insoluble metal sulfides.

## In prokaryotes

Disulfide bonds play an important protective role for bacteria as a reversible switch that turns a protein on or off when bacterial cells are exposed to oxidation reactions. Hydrogen peroxide (H2O2) in particular could severely damage DNA and kill the bacterium at low concentrations if it weren't for the protective action of the SS-bond. Subgroups Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular: bacterium) are microscopic, unicellular organisms. ... The most fundamental reactions in chemistry are the redox processes. ... Hydrogen peroxide (H2O2) is a very pale blue liquid which appears clear in a dilute solution, slightly more viscous than water. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the biological development of a cellular form of life or a virus. ... Subgroups Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular: bacterium) are microscopic, unicellular organisms. ...

## In rubber

Disulfide bonds also play a significant role in the vulcanization of rubber. Vulcanization, or curing, of rubber, is a chemical process in which individual polymer molecules are linked to other polymer molecules by atomic bridges. ... Latex being collected from a tapped rubber tree Rubber is an elastic hydrocarbon polymer which occurs as a milky colloidal suspension (known as latex) in the sap of several varieties of plants. ...

## In eukaryotes

In eukaryotic cells, disulfide bonds are generally formed in the lumen of the RER (rough endoplasmic reticulum) but not in the cytosol. This is due to the oxidative environment of the ER and the reducing environment of the cytosol (see glutathione). Thus disulfide bonds are mostly found in secretory proteins, lysosomal proteins, and the exoplasmic domains of membrane proteins. Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote is an organism with a complex cell or cells, in which the genetic material is organized into a membrane-bound nucleus or nuclei. ... The endoplasmic reticulum or ER (endoplasmic means within the cytoplasm, reticulum means little net) is an organelle found in all eukaryotic cells. ... ÃƒThe cytosol (as opposed fatty cytoplasm, which also includes the organelles) is the internal fluid of the cell, and a large part of cell metabolism occurs here. ... The endoplasmic reticulum (endoplasmic meaning within the cytoplasm, reticulum meaning little net in Latin) or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport (e. ... Skeletal formula of glutathione 3D model of glutathione Glutathione (GSH), whose IUPAC name is 2-amino-5-{[2-[(carboxymethyl)amino]- 1-(mercaptomethyl)-2-oxoethyl]amino}-5-oxopentanoic acid, is Î³-glutamylcysteinylglycine, a tripeptide. ...

There are notable exceptions to this rule. A number of cytosolic proteins have cysteine residues in proximity to each other that function as oxidation sensors; when the reductive potential of the cell fails, they oxidize and trigger cellular response mechanisms. Vaccinia virus also produces cytosolic proteins and peptides that have many disulfide bonds; although the reason for this is unknown presumably they have protective effects against intracellular proteolysis machinery. Vaccinia is the condition resulting from infection with the Vaccinia virus. ...

Disulfide bonds are also formed within and between protamines in the sperm chromatin of many mammalian species. Protamine is a drug that reverses the anticoagulant effects of heparin by binding to it. ... The signifier sperm can refer to: (mass noun, from Greek sperma = seed) a substance which consists of spermatozoa and which is a component of semen (mass noun) semen itself (informally, count noun with plural sperm or sperms) a single spermatozoon (= sperm cell) sperma ceti (Latin ceti, genitive of cetus = whale... Chromatin is a complex of DNA and protein found inside the nuclei of eukaryotic cells. ... Orders Multituberculata (extinct) Palaeoryctoides (extinct) Triconodonta (extinct) Subclass Australosphenida Ausktribosphenida Monotremata Subclass Eutheria (excludes extinct ancestors) Afrosoricida Anagaloidea (extinct) Arctostylopida (extinct) Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Cingulata Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Dinocerata (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Leptictida (extinct) Litopterna (extinct) Macroscelidea Mesonychia (extinct) Notoungulata...

## In hair

Hair is a biological polymer, with over 90% of its dry weight made of proteins called keratins. Under normal conditions, human hair contains around 10% water, which modifies its mechanical properties considerably. Hair proteins are held together by disulfide bonds, from the amino acid cysteine. These links are very robust: for example, virtually intact hair has been recovered from ancient Egyptian tombs. Different parts of the hair have different cysteine levels, leading to harder or softer material. Breaking and making disulfide bonds governs the phenomenon of wavy or frizzy hair. It is breaking and remaking of the disulfide bonds which is the basis for the permanent wave. Young Girl Fixing her Hair, by Sophie Gengembre Anderson Hair is a filamentous outgrowth of dead cells from the skin, found mainly in mammals. ... Microscopy of keratin filaments inside cells. ... Turn of the century advertisement for Nesslers permanent wave machine. ...

## References

• Sela M and Lifson S. (1959) "On the Reformation of Disulfide Bridges in Proteins", Biochimica et Biophysica Acta, 36, 471-478.
• Stark GR. (1977) "Cleavage at cysteine after cyanylation", Methods in Enzymology, 11, 238-255.
• Thornton JM. (1981) "Disulphide Bridges in Globular Proteins", Journal of Molecular Biology, 151, 261-287.
• Thannhauser TW, Konishi Y and Scheraga HA. (1984) "Sensitive Quantitative Analysis of Disulfide Bonds in Polypeptides and Proteins", Analytical Biochemistry, 138, 181-188.
• Wu J and Watson JT. (1998) "Optimization of the Cleavage Reaction for Cyanylated Cysteinyl Proteins for Eficient and Simplified Mas Mapping", Analytical Biochemistry, 258, 268-276.
• Futami J, Tada H, Seno M, Ishikami S and Yamada H. (2000) "Stabilization of Human RNase 1 by Introduction of a Disulfide Bond between Residues 4 and 118", J. Biochem., 128, 245-250.

Results from FactBites:

 Disulfide bond - Wikipedia, the free encyclopedia (1248 words) Disulfide bonds in proteins are formed between the thiol groups of cysteine residues. The prototype of a protein disulfide bond is the two-amino-acid peptide, cystine, which is composed of two cysteine amino acids joined by a disulfide bond (shown in Figure 2 in its unionized form). Disulfide bonds play an important protective role for bacteria as a reversible switch that turns a protein on or off when bacterial cells are exposed to oxidation reactions.
 Disulfide - Wikipedia, the free encyclopedia (270 words) In chemistry, a disulfide ion is an anion (negatively-charged ion) formed by two sulfur atoms having an overall -2 charge. In many cases, each of the two sulfur atoms in a disulfide group is covalently bonded to a carbon atom in an organic compound, forming a disulfide bond, sometimes called a disulfide linkage or a disulfide bridge. Examples of organic compounds containing a disulfide bond or group are the biological amino acid cystine and lipoic acid.
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