ALDH3A1 | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Aliases | ALDH3A1 , ALDH3, ALDHIII, aldehyde dehydrogenase 3 family member A1, Aldehyde dehydrogenase 3 family, member A1 | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 100660 MGI: 1353451 HomoloGene: 20175 GeneCards: ALDH3A1 | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Aldehyde dehydrogenase, dimeric NADP-preferring is an enzyme that in humans is encoded by the ALDH3A1 gene. [5] [6] [7]
Aldehyde dehydrogenases oxidize various aldehydes to the corresponding acids. They are involved in the detoxification of alcohol-derived acetaldehyde and in the metabolism of corticosteroids, biogenic amines, neurotransmitters, and lipid peroxidation. The enzyme encoded by this gene forms a cytoplasmic homodimer that preferentially oxidizes aromatic aldehyde substrates. The gene is located within the Smith–Magenis syndrome region on chromosome 17. [7]
ALDH3A1 expression is notably high in the cornea of mammalian species, comprising from 5 to 50% of soluble protein content, but is almost absent from the cornea of other vertebrates. [8]
ALDH3A1 is a homodimer consisting of alpha helices (43.8%), beta sheets (4.2%), p-loop turns (28.2%) and random coils (23.8%). [9] The catalytic residue–Cys244—is located on an active site that contains a Rossmann fold that binds the enzyme's cofactor, NAD(P)+. [10]
ALDH3A1's catalytic mechanism mirrors that of other enzymes of the aldehyde dehydrogenase family. The sulfur atom of Cys244 attacks the carbonyl of the aldehyde substrate in a nucleophilic attack that releases a hydride ion. The hydride ion is accepted by the NAD(P)+ bound to the Rossmann fold. Unique interactions between the cofactor and the Rossmann fold facilitate an isomerization of the enzyme that releases the cofactor while maintaining the integrity of the active site. [11] A water molecule enters the active site and is subsequently activated by a glutamate residue. The activated water then attacks the thioester enzyme-substrate complex in nucleophilic reaction that regenerates the free enzyme, and releases the corresponding carboxylic acid.
Electronic excitations of alkene and aromatic functional groups allow certain nucleic acids, proteins, fatty acids and organic molecules to absorb ultraviolet radiation (UVR). Moderate UVR exposure oxidizes specific proteins that eventually serve as signaling agents for an array of metabolic and inflammatory pathways. [9] Overexposure to UVR, on the other hand, can be detrimental to the tissue. In the presence of molecular oxygen, UVR leads to the formation of reactive oxygen species (ROS) that are implicated in many degradation pathways. [12] In the case of lipid peroxidation, ROS react with polyunsaturated fatty acids situated in the lipid bilayer of the cell membrane to produce lipid radicals. These lipid radicals propagate, further damaging the lipid bilayer and producing lipid hydroperoxides. The eventual degradation of lipid hydroperoxides releases a wide variety of aldehydes, which, owing to their stability and ability to react cellular nucleophiles, [12] are both cytotoxic and genotoxic in nature. ALDH3A1 plays a critical role in the metabolism of these aldehydes to their corresponding carboxylic acids in mammalian cornea and saliva. 4-Hydroxynonenal (4HNE)—which ALDH3A1 metabolizes with Vmax of 27,754 moles NADPH/min•mg and an apparent Km of 362 micromolar [9] —is the most abundant aldehyde produced in the LPO of arachidonic acid and linoleic acid. [13] [14] Its stability and multiple sites of reactivity (carbon-carbon double bond, hydroxyl group, and carbonyl) make 4HNE a potent inhibitor of cellular growth, enzyme activities, calcium sequestration, and protein synthesis. It is also involved in the consumption of glutathione and the alteration of signal transduction and gene expression. [15] [16] [17] [18] [19]
ALDH3A1 comprises approximately 10-40% of the water-soluble protein in the mammalian cornea. [20] [21] Direct exposure to UVR and molecular oxygen, make the cornea susceptible to ROS and 4HNE. Studies in which rabbits were transfected with genes that allow them to overexpress human ALDH3A1 in their corneal stromal fibroblasts document ALDH3A1's most critical function is to protect the cornea from oxidative stresses. In the cornea ALDH3A1: (1) prevents the formation of 4-HNE protein adducts that would impeded proteins’ function; (2) is more effective at metabolizing 4-HNE than other comparable agents such as glutathione (GSH); (3) protects the corneal cells from 4-HNE induced apoptosis; (4) reduces consumption of GSH by relieving 4HNE GSH adducts; (5) and relieves 4-HNE's inhibition of the 20S protease activity. [22]
However, only a fraction of the total concentration of ALDH3A1 in the cornea is used for metabolizing aldehydes. This observation has sparked multiple investigations of ALDH3A1's role beyond aldehyde metabolism. [23] Although the full scope of ALDH3A1's function is yet to be firmly established, there is strong evidence suggesting that ALDH3A1 serves to maintain the cellular redox balance as well as the structural integrity and transparency of the cornea. One study elucidates that ALDH3A1 not only indirectly protects the cornea from UVR induced oxidative stress by metabolizing aldehydes, but also protects the tissue directly, by competitively absorbing UVR in a “suicide response” [8] that reduces damage to other proteins of the cornea [9] In fact, 50% percent of the UVR that the cornea is exposed to is absorbed by ADLH3A1. ALDH3A1's absorption of UVR oxidizes several key amino acid residues, leading to conformational changes that convert the alpha and beta sheets into random coils. These conformational changes ultimately relieve the dimer structure. This loss of secondary and tertiary structure leads to protein aggregation and complete loss of enzymatic activity. [9] Peptide mapping and spectroscopic experiments reveal that the loss of activity is not a result of Cys244 oxidation (which, together with the active site, remains intact during photo-excitation), but instead, due to the degradation of other key amino residues (most notably methionine and tryptophan). These amino acid residues degrade under oxidative stress, leading to the formation of non-reducible cross-links that stabilize the soluble aggregates. [9] Tryptophan for instance is doubly oxidized to generate ROSs such as H2O2, which elicit further oxidation and adduction. [24] Nevertheless, the abundance of ALDH3A1 in the cornea ensures that this suicide response neither impedes with aldehyde metabolism nor leads to the formation of insoluble aggregates that would affect the transparency of the cornea. [25]
Further clarification of ALDH3A1's role in the cornea has been provided by gene-knockout studies in which genes encoding ALDH3A1 were removed from the mice genome. It was found that ALDH3A1-null mice exhibited lower proteasome activity, higher rates of protein degradation/oxidation, and higher GSH, 4HNE and malondialdehyde protein adduct levels—all of which contributed to the development of cataracts and opacities in the subscapular regions of the cornea within one month of age. [23] These observations on ALDH3A1-null mice reaffirm that ALDH3A1's role extends beyond enzymatic metabolism; encompassing functions in maintenance of the structural integrity and transparency of the cornea.
Glutathione is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, peroxides, lipid peroxides, and heavy metals. It is a tripeptide with a gamma peptide linkage between the carboxyl group of the glutamate side chain and cysteine. The carboxyl group of the cysteine residue is attached by normal peptide linkage to glycine.
Xanthine oxidase is a form of xanthine oxidoreductase, a type of enzyme that generates reactive oxygen species. These enzymes catalyze the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid. These enzymes play an important role in the catabolism of purines in some species, including humans.
4-Hydroxynonenal, or 4-hydroxy-2E-nonenal or 4-hydroxy-2-nonenal or 4-HNE or HNE,, is an α,β-unsaturated hydroxyalkenal that is produced by lipid peroxidation in cells. 4-HNE is the primary α,β-unsaturated hydroxyalkenal formed in this process. It is a colorless oil. It is found throughout animal tissues, and in higher quantities during oxidative stress due to the increase in the lipid peroxidation chain reaction, due to the increase in stress events. 4-HNE has been hypothesized to play a key role in cell signal transduction, in a variety of pathways from cell cycle events to cellular adhesion.
Malondialdehyde belong to the class of β-dicarbonyls. A colorless liquid, malondialdehyde is a highly reactive compound that occurs as the enol. It is a physiological metabolite, and a marker for oxidative stress.
Aldehyde dehydrogenases are a group of enzymes that catalyse the oxidation of aldehydes. They convert aldehydes to carboxylic acids. The oxygen comes from a water molecule. To date, nineteen ALDH genes have been identified within the human genome. These genes participate in a wide variety of biological processes including the detoxification of exogenously and endogenously generated aldehydes.
Ethanol, an alcohol found in nature and in alcoholic drinks, is metabolized through a complex catabolic metabolic pathway. In humans, several enzymes are involved in processing ethanol first into acetaldehyde and further into acetic acid and acetyl-CoA. Once acetyl-CoA is formed, it becomes a substrate for the citric acid cycle ultimately producing cellular energy and releasing water and carbon dioxide. Due to differences in enzyme presence and availability, human adults and fetuses process ethanol through different pathways. Gene variation in these enzymes can lead to variation in catalytic efficiency between individuals. The liver is the major organ that metabolizes ethanol due to its high concentration of these enzymes.
Fatty aldehyde dehydrogenase is an aldehyde dehydrogenase enzyme that in human is encoded in the ALDH3A2 gene on chromosome 17. Aldehyde dehydrogenase enzymes function to remove toxic aldehydes that are generated by the metabolism of alcohol and by lipid peroxidation.
Aldehyde dehydrogenase, mitochondrial is an enzyme that in humans is encoded by the ALDH2 gene located on chromosome 12. ALDH2 belongs to the aldehyde dehydrogenase family of enzymes. Aldehyde dehydrogenase is the second enzyme of the major oxidative pathway of alcohol metabolism. ALDH2 has a low Km for acetaldehyde, and is localized in mitochondrial matrix. The other liver isozyme, ALDH1, localizes to the cytosol.
Alcohol dehydrogenase 1B is an enzyme that in humans is encoded by the ADH1B gene.
The glyoxalase system is a set of enzymes that carry out the detoxification of methylglyoxal and the other reactive aldehydes that are produced as a normal part of metabolism. This system has been studied in both bacteria and eukaryotes. This detoxification is accomplished by the sequential action of two thiol-dependent enzymes; firstly glyoxalase І, which catalyzes the isomerization of the spontaneously formed hemithioacetal adduct between glutathione and 2-oxoaldehydes into S-2-hydroxyacylglutathione. Secondly, glyoxalase ІІ hydrolyses these thiolesters and in the case of methylglyoxal catabolism, produces D-lactate and GSH from S-D-lactoyl-glutathione.
Alcohol dehydrogenase [NADP+] also known as aldehyde reductase or aldo-keto reductase family 1 member A1 is an enzyme that in humans is encoded by the AKR1A1 gene. AKR1A1 belongs to the aldo-keto reductase (AKR) superfamily. It catalyzes the NADPH-dependent reduction of a variety of aromatic and aliphatic aldehydes to their corresponding alcohols and catalyzes the reduction of mevaldate to mevalonic acid and of glyceraldehyde to glycerol. Mutations in the AKR1A1 gene has been found associated with non-Hodgkin's lymphoma.
Glutathione S-transferase A4, also known as GSTA4, is an enzyme which in humans is encoded by the GSTA4 gene.
Alcohol dehydrogenase 1A is an enzyme that in humans is encoded by the ADH1A gene.
Aldehyde dehydrogenase 7 family, member A1, also known as ALDH7A1 or antiquitin, is an enzyme that in humans is encoded by the ALDH7A1 gene. The protein encoded by this gene is a member of subfamily 7 in the aldehyde dehydrogenase gene family. These enzymes are thought to play a major role in the detoxification of aldehydes generated by alcohol metabolism and lipid peroxidation. This particular member has homology to a previously described protein from the green garden pea, the 26g pea turgor protein. It is also involved in lysine catabolism that is known to occur in the mitochondrial matrix. Recent reports show that this protein is found both in the cytosol and the mitochondria, and the two forms likely arise from the use of alternative translation initiation sites. An additional variant encoding a different isoform has also been found for this gene. Mutations in this gene are associated with pyridoxine-dependent epilepsy. Several related pseudogenes have also been identified.
Aldehyde dehydrogenase 3 family, member B1 also known as ALDH3B1 is an enzyme that in humans is encoded by the ALDH3B1 gene.
Aldehyde dehydrogenase 1 family, member A3, also known as ALDH1A3 or retinaldehyde dehydrogenase 3 (RALDH3), is an enzyme that in humans is encoded by the ALDH1A3 gene,
Aldehyde dehydrogenase 1 family, member A1, also known as ALDH1A1 or retinaldehyde dehydrogenase 1 (RALDH1), is an enzyme that is encoded by the ALDH1A1 gene.
Protein moonlighting is a phenomenon by which a protein can perform more than one function. It is an excellent example of gene sharing.
Acyl-CoA thioesterase 6 is a protein that in humans is encoded by the ACOT6 gene. The protein, also known as C14orf42, is an enzyme with thioesterase activity.
Reactive aldehyde species (RASP), also known as reactive aldehydes, refer to a class of electrophilic organic aldehyde molecules that are generally toxic or facilitate inflammation. RASP covalently react with amine groups and thiol groups, particularly in proteins. Following threshold amounts of binding to the electrophile-responsive proteome, RASP modify protein function, as has been described with MAP kinase, protein kinase C, and other proteins that potentiate cytokine release and other aspects of inflammation. Binding of RASP to proteins can also lead to NF-kB activation, autoantibody formation, inflammasome activation, and activation of Scavenger Receptor A. RASP are formed via a variety of processes, including oxidation of alcohols, polyamine metabolism and lipid peroxidation. In addition to binding to proteins and other amine or thiol-containing molecules such as glutathione, RASP are metabolized by aldehyde dehydrogenases or aldehyde reductases. Due to the toxicity of RASP, only a small number of genetic mutations in aldehyde dehydrogenases allow for viable offspring, resulting in Sjögren-Larsson Syndrome, Succinic Semi-Aldehyde Dehydrogenase Deficiency, and other rare diseases.