Lysine (abbreviated as Lys or K), encoded by the codons AAA and AAG, is an ?-amino acid that is used in the biosynthesis of proteins. It contains an ?-amino group (which is in the protonated -NH3+ form under biological conditions), an ?-carboxylic acid group (which is in the deprotonated -COO- form under biological conditions), and a side chain lysyl ((CH2)4NH2), classifying it as a charged (at physiological pH), aliphatic amino acid. It is essential in humans, meaning the body cannot synthesize it and thus it must be obtained from the diet.
Lysine is a base, as are arginine and histidine. The ?-amino group often participates in hydrogen bonding and as a general base in catalysis. The ?-ammonium group (NH3+) is attached to the fourth carbon from the ?-carbon, which is attached to the carboxyl (C=OOH) group.
Common posttranslational modifications include methylation of the ?-amino group, giving methyl-, dimethyl-, and trimethyllysine (the latter occurring in calmodulin); also acetylation, sumoylation, ubiquitination, and hydroxylation - producing the hydroxylysine in collagen and other proteins. O-Glycosylation of hydroxylysine residues in the endoplasmic reticulum or Golgi apparatus is used to mark certain proteins for secretion from the cell. In opsins like rhodopsin and the visual opsins (encoded by the genes OPN1SW, OPN1MW, and OPN1LW), retinaldehyde forms a Schiff base with a conserved lysine residue, and interaction of light with the retinylidene group causes signal transduction in color vision (See visual cycle for details). Deficiencies may cause blindness, as well as many other problems due to its ubiquitous presence in proteins.
Video Lysine
Biosynthesis
As an essential amino acid, lysine is not synthesized in animals, hence it must be ingested as lysine or lysine-containing proteins. In plants and most bacteria, it is synthesized from aspartic acid (aspartate):
- L-aspartate is first converted to L-aspartyl-4-phosphate by aspartokinase (or aspartate kinase). ATP is needed as an energy source for this step.
- ?-Aspartate semialdehyde dehydrogenase converts this into ?-aspartyl-4-semialdehyde (or ?-aspartate-4-semialdehyde). Energy from NADPH is used in this conversion.
- 4-hydroxy-tetrahydrodipicolinate synthase adds a pyruvate group to the ?-aspartyl-4-semialdehyde, and a water molecule is removed. This causes cyclization and gives rise to (2S,4S)-4-hydroxy-2,3,4,5-tetrahydrodipicolinate.
- This product is reduced to 2,3,4,5-tetrahydrodipicolinate (or ?1-piperidine-2,6-dicarboxylate, in the figure: (S)-2,3,4,5-tetrahydropyridine-2,6-dicarboxylate) by 4-hydroxy-tetrahydrodipicolinate reductase. This reaction consumes an NADPH molecule and releases a second water molecule.
- Tetrahydrodipicolinate N-acetyltransferase opens this ring and gives rise to N-succinyl-L-2-amino-6-oxoheptanedionate (or N-acyl-2-amino-6-oxopimelate). Two water molecules and one acyl-CoA (succinyl-CoA) enzyme are used in this reaction.
- N-succinyl-L-2-amino-6-oxoheptanedionate is converted into N-succinyl-LL-2,6-diaminoheptanedionate (N-acyl-2,6-diaminopimelate). This reaction is catalyzed by the enzyme succinyl diaminopimelate aminotransferase. A glutamic acid molecule is used in this reaction and an oxoacid is produced as a byproduct.
- N-succinyl-LL-2,6-diaminoheptanedionate (N-acyl-2,6-diaminopimelate)is converted into LL-2,6-diaminoheptanedionate (L,L-2,6-diaminopimelate) by succinyl diaminopimelate desuccinylase (acyldiaminopimelate deacylase). A water molecule is consumed in this reaction and a succinate is produced a byproduct.
- LL-2,6-diaminoheptanedionate is converted by diaminopimelate epimerase into meso-2,6-diamino-heptanedionate (meso-2,6-diaminopimelate).
- Finally, meso-2,6-diamino-heptanedionate is converted into L-lysine by diaminopimelate decarboxylase.
Enzymes involved in this biosynthesis include:
- Aspartokinase
- Aspartate-semialdehyde dehydrogenase
- 4-hydroxy-tetrahydrodipicolinate synthase
- 4-hydroxy-tetrahydrodipicolinate reductase
- 2,3,4,5-tetrahydropyridine-2,6-dicarboxylate N-succinyltransferase
- Succinyldiaminopimelate transaminase
- Succinyl-diaminopimelate desuccinylase
- Diaminopimelate epimerase
- Diaminopimelate decarboxylase.
It is worth noting, however, that in fungi, euglenoids and some prokaryotes lysine is synthesized via the alpha-aminoadipate pathway.
Maps Lysine
Metabolism
Lysine is metabolised in mammals to give acetyl-CoA, via an initial transamination with ?-ketoglutarate. The bacterial degradation of lysine yields cadaverine by decarboxylation.
Allysine is a derivative of lysine, used in the production of elastin and collagen. It is produced by the actions of the enzyme lysyl oxidase on lysine in the extracellular matrix and is essential in the crosslink formation that stabilizes collagen and elastin.
Requirements
The Food and Nutrition Board (FNB) of the U.S. Institute of Medicine set Recommended Dietary Allowances (RDAs) for essential amino acids in 2002. For lysine, for adults 19 years and older, 38 mg/kg body weight/day.
Synthesis
Synthetic, racemic lysine has long been known. A practical synthesis starts from caprolactam. Industrially, L-lysine is usually manufactured by a fermentation process using Corynebacterium glutamicum; production exceeds 600,000 tons a year.
L-lysine HCl is used as a dietary supplement, providing 80.03% L-lysine. As such, 1 g of L-lysine is contained in 1.25 g of L-lysine HCl.
Dietary sources
The nutritional requirement per day, in milligrams of lysine per kilogram of body weight, is: infants (3-4 months) 103 mg/kg, children (2 years) 64 mg/kg, older children (10-12 years) 44 to 60 mg/kg, adults 12 mg/kg. For a 70 kg adult, 12 milligrams of lysine per kilogram of body weight is 0.84 grams of lysine. Recommendations for adults have been revised upwards to 30 mg/kg.
Good sources of lysine are high-protein foods such as eggs, meat (specifically red meat, lamb, pork, and poultry), soy, beans and peas, cheese (particularly Parmesan), and certain fish (such as cod and sardines).
Lysine is the limiting amino acid (the essential amino acid found in the smallest quantity in the particular foodstuff) in most cereal grains, but is plentiful in most pulses (legumes). A vegetarian or low animal protein diet can be adequate for protein, including lysine, if it includes both cereal grains and legumes, but there is no need for the two food groups to be consumed in the same meals.
A food is considered to have sufficient lysine if it has at least 51 mg of lysine per gram of protein (so that the protein is 5.1% lysine). Foods containing significant proportions of lysine include:
Properties
L-Lysine plays a major role in calcium absorption; building muscle protein; recovering from surgery or sports injuries; and the body's production of hormones, enzymes, and antibodies.
Modifications
Lysine can be modified through acetylation (acetyllysine), methylation (methyllysine), ubiquitination, sumoylation, neddylation, biotinylation, pupylation, and carboxylation, which tends to modify the function of the protein of which the modified lysine residue(s) are a part.
Clinical significance
A review cited some studies showing that lysine supplementation can decrease herpes simplex cold sore outbreaks and reduce healing time. However, an authoritative Cochrane Review published in 2015 concluded there is insufficient evidence that lysine supplementation is effective against herpes simplex virus; it has not been approved by the FDA for herpes simplex suppression.
Use of lysine in animal feed
Lysine production for animal feed is a major global industry, reaching in 2009 almost 700,000 tonnes for a market value of over EUR1.22 billion. Lysine is an important additive to animal feed because it is a limiting amino acid when optimizing the growth of certain animals such as pigs and chickens for the production of meat. Lysine supplementation allows for the use of lower-cost plant protein (maize, for instance, rather than soy) while maintaining high growth rates, and limiting the pollution from nitrogen excretion. In turn, however, phosphate pollution is a major environmental cost when corn is used as feed for poultry and swine.
Lysine is industrially produced by microbial fermentation, from a base mainly of sugar. Genetic engineering research is actively pursuing bacterial strains to improve the efficiency of production and allow lysine to be made from other substrates.
In popular culture
The 1993 film Jurassic Park (based on the 1990 Michael Crichton novel of the same name) features dinosaurs that were genetically altered so that they could not produce lysine. This was known as the "lysine contingency" and was supposed to prevent the cloned dinosaurs from surviving outside the park, forcing them to be dependent on lysine supplements provided by the park's veterinary staff. In reality, no animals are capable of producing lysine (it is an essential amino acid).
Lysine is the favorite amino acid of the character Sheldon Cooper in the television show, The Big Bang Theory. It was mentioned in season 2, episode 13, "The Friendship Algorithm".
In 1996, lysine became the focus of a price-fixing case, the largest in United States history. The Archer Daniels Midland Company paid a fine of US$100 million, and three of its executives were convicted and served prison time. Also found guilty in the price-fixing case were two Japanese firms (Ajinomoto, Kyowa Hakko) and a South Korean firm (Sewon). Secret video recordings of the conspirators fixing lysine's price can be found online or by requesting the video from the U.S. Department of Justice, Antitrust Division. This case served as the basis of the movie The Informant!, and a book of the same title.
See also
- Acetyllysine
- Deamination
- Methyllysine
- Saccharopine
References
Sources
- Much of the information in this article has been translated from German Wikipedia.
- Lide, D. R., ed. (2002). CRC Handbook of Chemistry and Physics (83rd ed.). Boca Raton, FL: CRC Press. ISBN 0-8493-0483-0.
Source of the article : Wikipedia
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