Cysteine

Source: Wikipedia, the free encyclopedia.
(Redirected from
Cys
)
Not to be confused with
Sistine
.
"Cys" redirects here. For other uses, see Cys (disambiguation).
l-Cysteine

Skeletal formula of L-cysteine
Names
IUPAC name
Cysteine
Other names
  • 2-Amino-3-sulfhydrylpropanoic acid
Identifiers
3D model (
JSmol
)
Abbreviations Cys, C
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.000.145 Edit this at Wikidata
EC Number
  • 200-158-2
E number E920 (glazing agents, ...)
IUPHAR/BPS
KEGG
UNII
  • InChI=1S/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6) checkY
    Key: XUJNEKJLAYXESH-UHFFFAOYSA-N checkY
  • InChI=1/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)/t2-/m0/s1
    Key: XUJNEKJLAYXESH-REOHCLBHBU
  • InChI=1/C3H7NO2S/c4-2(1-7)3(5)6/h2,7H,1,4H2,(H,5,6)
    Key: XUJNEKJLAYXESH-UHFFFAOYAC
  • C([C@@H](C(=O)O)N)S
  • Zwitterion: C([C@@H](C(=O)[O-])[NH3+])S
Properties[3]
C3H7NO2S
Molar mass 121.15 g·mol−1
Appearance white crystals or powder
Melting point 240 °C (464 °F; 513 K) decomposes
277g/L (at 25 °C) 
[1]
Solubility 1.5g/100g ethanol 19 °C [2]
+9.4° (H2O, c = 1.3)
Supplementary data page
Cysteine (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Cysteine (symbol Cys or C;

enzymatic reactions as a nucleophile. Cysteine is chiral, but interestingly, both D and L-cysteine are found in nature with D-cysteine having been found in developing brain (see Semenza et al., 2021). Cysteine is named after its discovery in urine, which comes from the urinary bladder or cyst, from kystis "bladder".[7]

The thiol is susceptible to oxidation to give the

disulfide derivative cystine, which serves an important structural role in many proteins. In this case, the symbol Cyx is sometimes used.[8][9] The deprotonated form can generally be described by the symbol Cym as well.[9][10]

When used as a food additive, cysteine has the E number E920.

Cysteine is

codons
UGU and UGC.

Structure

Like other amino acids (not as a residue of a protein), cysteine exists as a

chirality in the older d/l notation based on homology to d- and l-glyceraldehyde. In the newer R/S system of designating chirality, based on the atomic numbers of atoms near the asymmetric carbon, cysteine (and selenocysteine) have R chirality, because of the presence of sulfur (or selenium) as a second neighbor to the asymmetric carbon atom. The remaining chiral amino acids, having lighter atoms in that position, have S chirality. Replacing sulfur with selenium gives selenocysteine
.

(R)-Cysteine (left) and (S)-Cysteine (right) in zwitterionic form at neutral pH

Dietary sources

Cysteinyl is a residue in high-protein foods. Some foods considered rich in cysteine include poultry, eggs, beef, and whole grains. In high-protein diets, cysteine may be partially responsible for reduced blood pressure and stroke risk.[11] Although classified as a nonessential amino acid, in rare cases, cysteine may be essential for infants, the elderly, and individuals with certain metabolic diseases or who suffer from malabsorption syndromes. Cysteine can usually be synthesized by the human body under normal physiological conditions if a sufficient quantity of methionine is available.

Industrial sources

The majority of l-cysteine is obtained industrially by

Evonik (formerly Degussa) introduced a route from substituted thiazolines.[15] Following this technology, l-cysteine is produced by the hydrolysis of racemic 2-amino-Δ2-thiazoline-4-carboxylic acid using Pseudomonas thiazolinophilum.[16]

Biosynthesis

Cysteine synthesis: Cystathionine beta synthase catalyzes the upper reaction and cystathionine gamma-lyase catalyzes the lower reaction.

In animals, biosynthesis begins with the amino acid

serine transacetylase. The enzyme cysteine synthase, using sulfide sources, converts this ester into cysteine, releasing acetate.[17]

Biological functions

The cysteine sulfhydryl group is

thiolate form in the cell.[18]
Because of its high reactivity, the sulfhydryl group of cysteine has numerous biological functions.

Precursor to the antioxidant glutathione

Due to the ability of thiols to undergo redox reactions, cysteine and cysteinyl residues have antioxidant properties. Its antioxidant properties are typically expressed in the tripeptide glutathione, which occurs in humans and other organisms. The systemic availability of oral glutathione (GSH) is negligible; so it must be biosynthesized from its constituent amino acids, cysteine, glycine, and glutamic acid. While glutamic acid is usually sufficient because amino acid nitrogen is recycled through glutamate as an intermediary, dietary cysteine and glycine supplementation can improve synthesis of glutathione.[19]

Precursor to iron-sulfur clusters

Cysteine is an important source of

iron-sulfur clusters and in nitrogenase is extracted from cysteine, which is converted to alanine in the process.[20]

Metal ion binding

Beyond the iron-sulfur proteins, many other metal cofactors in enzymes are bound to the thiolate substituent of cysteinyl residues. Examples include zinc in

heavy metals, so that proteins containing cysteine, such as metallothionein, will bind metals such as mercury, lead, and cadmium tightly.[22]

Roles in protein structure

In the translation of messenger RNA molecules to produce polypeptides, cysteine is coded for by the UGU and UGC

codons
.

Cysteine has traditionally been considered to be a

hydroxyl groups in the side chains of other polar amino acids. However, the cysteine side chain has been shown to stabilize hydrophobic interactions in micelles to a greater degree than the side chain in the nonpolar amino acid glycine and the polar amino acid serine.[23] In a statistical analysis of the frequency with which amino acids appear in various proteins, cysteine residues were found to associate with hydrophobic regions of proteins. Their hydrophobic tendency was equivalent to that of known nonpolar amino acids such as methionine and tyrosine (tyrosine is polar aromatic but also hydrophobic[24]), those of which were much greater than that of known polar amino acids such as serine and threonine.[25] Hydrophobicity scales, which rank amino acids from most hydrophobic to most hydrophilic, consistently place cysteine towards the hydrophobic end of the spectrum, even when they are based on methods that are not influenced by the tendency of cysteines to form disulfide bonds in proteins. Therefore, cysteine is now often grouped among the hydrophobic amino acids,[26][27] though it is sometimes also classified as slightly polar,[28] or polar.[6]

Most cysteine residues are covalently bonded to other cysteine residues to form

reducing environments, disulfide bonds are generally unstable in the cytosol
with some exceptions as noted below.

Figure 2: Cystine (shown here in its neutral form), two cysteines bound together by a disulfide bond

Disulfide bonds in proteins are formed by oxidation of the sulfhydryl group of cysteine residues. The other sulfur-containing amino acid, methionine, cannot form disulfide bonds. More aggressive oxidants convert cysteine to the corresponding sulfinic acid and sulfonic acid. Cysteine residues play a valuable role by crosslinking proteins, which increases the rigidity of proteins and also functions to confer proteolytic resistance (since protein export is a costly process, minimizing its necessity is advantageous). Inside the cell, disulfide bridges between cysteine residues within a polypeptide support the protein's tertiary structure. Insulin is an example of a protein with cystine crosslinking, wherein two separate peptide chains are connected by a pair of disulfide bonds.

disulfide bonds; the cell transfers dehydroascorbic acid to the endoplasmic reticulum
, which oxidizes the environment. In this environment, cysteines are, in general, oxidized to cystine and are no longer functional as a nucleophiles.

Aside from its oxidation to cystine, cysteine participates in numerous

Inteins
often function with the help of a catalytic cysteine. These roles are typically limited to the intracellular milieu, where the environment is reducing, and cysteine is not oxidized to cystine.

Applications

Cysteine, mainly the l-

processing aid for baking.[31]

In the field of personal care, cysteine is used for

permanent-wave applications, predominantly in Asia. Again, the cysteine is used for breaking up the disulfide bonds in the hair's keratin
.

Cysteine is a very popular target for site-directed labeling experiments to investigate biomolecular structure and dynamics.

Michael addition. Site-directed spin labeling
for EPR or paramagnetic relaxation-enhanced NMR also uses cysteine extensively.

Reducing toxic effects of alcohol

Cysteine has been proposed as a preventive or antidote for some of the negative effects of alcohol, including liver damage and hangover. It counteracts the poisonous effects of acetaldehyde.[32] Cysteine supports the next step in metabolism, which turns acetaldehyde into acetic acid.[citation needed]

In a

control group had a 10% survival rate.[33]

In 2020 an article was published that suggests L-cysteine might also work in humans.[34]

N-Acetylcysteine

acetaminophen overdose.[35]

Sheep

Cysteine is required by

transgenic sheep that can make their own cysteine have been developed.[36]

Chemical reactions

Being multifunctional, cysteine undergoes a variety of reactions. Much attention has focused on protecting the sulfhydryl group.[37] Methylation of cysteine gives S-methylcysteine. Treatment with formaldehyde gives the thiazolidine thioproline. Cysteine forms a variety of coordination complexes upon treatment with metal ions.[38]

Safety

Relative to most other amino acids, cysteine is much more toxic.[39]

Dietary restrictions

The animal-originating sources of l-cysteine as a food additive are a point of contention for people following dietary restrictions such as kosher, halal, vegan, or vegetarian.[40] To avoid this problem, l-cysteine can also be sourced from microbial or other synthetic processes.

History

In 1884 German chemist

dimer of a monomer which he named "cysteïne".[41]

See also

Wikimedia Commons has media related to Cysteine.

References

  1. ^ "PubChem data".
  2. ISBN 9783540699330
    .
  3. ISBN 0-8493-0462-8
    ..
  4. doi:10.1351/pac198456050595
  5. ^ "cysteine - Definition of cysteine in English by Oxford Dictionaries". Oxford Dictionaries - English. Archived from the original on September 25, 2016. Retrieved 15 April 2018.
  6. ^ a b "The primary structure of proteins is the amino acid sequence". The Microbial World. University of Wisconsin-Madison Bacteriology Department. Archived from the original on 25 May 2013. Retrieved 16 September 2012.
  7. ISSN 0307-4412
    .
  8. ^ "Amber Workshop - Tutorial A1 - Section 1: Do some editing of the PDB file". ambermd.org. Archived from the original on 2022-05-22. Retrieved 2022-06-02.
  9. ^
    S2CID 220796795
    .
  10. ^ "Amber Workshop - Tutorial A1 - Section 1: Do some editing of the PDB file". ambermd.org. Archived from the original on 2022-05-22. Retrieved 2022-06-02.
  11. S2CID 14895681
    .
  12. ^ "EU Chemical Requirements". Retrieved May 24, 2020. ...L-cysteine hydrochloride or hydrochloride monohydrate. Human hair may not be used as a source for this substance
  13. ^ "Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009 on cosmetic products". Retrieved July 28, 2021. ...ANNEX II LIST OF SUBSTANCES PROHIBITED IN COSMETIC PRODUCTS...416 Cells, tissues or products of human origin
  14. ^ "Questions About Food Ingredients: What is L-cysteine/cysteine/cystine?". Vegetarian Resource Group.
  15. doi:10.1002/anie.198106681
    .
  16. ISBN 978-3-527-30673-2
    .
  17. S2CID 2539629
    .
  18. PMID 9636038
    .
  19. PMID 21795440. Open access icon
  20. PMID 16824008
    .
  21. ISBN 978-0-935702-73-6.[page needed
    ]
  22. PMID 3298579
    .
  23. PMID 5650851
    .
  24. ^ "A Review of Amino Acids (tutorial)". Curtin University. Archived from the original on 2015-09-07. Retrieved 2015-09-09.
  25. S2CID 34980474
    .
  26. ^ Betts, M.J.; R.B. Russell (2003). "Hydrophobic amino acids". Amino Acid Properties and Consequences of Substitutions, In: Bioinformatics for Geneticists. Wiley. Retrieved 2012-09-16.
  27. ^ Gorga, Frank R. (1998–2001). "Introduction to Protein Structure--Non-Polar Amino Acids". Archived from the original on 2012-09-05. Retrieved 2012-09-16.
  28. ^ "Virtual Chembook--Amino Acid Structure". Elmhurst College. Archived from the original on 2012-10-02. Retrieved 2012-09-16.
  29. S2CID 2885059
    .
  30. ISBN 978-0-203-90808-2
    .
  31. ^ "Food Ingredients and Colors". U.S. Food and Drug Administration. November 2004. Archived from the original on 2009-05-12. Retrieved 2009-09-06.
  32. PMID 30925182
    .
  33. S2CID 5924137
    .
  34. PMID 32808029
    .
  35. S2CID 9209528
    .
  36. PMID 7569041
    .
  37. doi:10.15227/orgsyn.059.0190
    .
  38. doi:10.1021/ic00343a061
    .
  39. PMID 3309557
    .
  40. ^ "Kosher View of L-Cysteine". kashrut.com. May 2003.
  41. ^ Baumann, E. (1884). "Ueber Cystin und Cysteïn" [On cystine and cysteine]. Zeitschrift für physiologische Chemie (in German). 8: 299–305. From pp. 301-302: "Die Analyse der Substanz ergibt Werthe, welche den vom Cystin (C6H12N2S2O4) verlangten sich nähern, […] nenne ich dieses Reduktionsprodukt des Cystins: Cysteïn." (Analysis of the substance [cysteine] reveals values which approximate those [that are] required by cystine (C6H12N2S2O4), however the new base [cysteine] can clearly be recognized as a reduction product of cystine, to which the [empirical] formula C3H7NSO2, [which had] previously [been] ascribed to cystine, is [now] ascribed. In order to indicate the relationships of this substance to cystine, I name this reduction product of cystine: "cysteïne".) Note: Baumann's proposed structures for cysteine and cystine (see p.302) are incorrect: for cysteine, he proposed CH3CNH2(SH)COOH .

Further reading

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Cysteine&oldid=1218135653"
This page is based on the copyrighted Wikipedia article: Cys. Articles is available under the CC BY-SA 3.0 license; additional terms may apply.Privacy Policy