Names | |
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IUPAC name 3′-O-Phosphonoadenosine 5′-{(3R)-3-hydroxy-2,2-dimethyl-4-oxo-4-[(3-oxo-3-{[2-(propanoylsulfanyl)ethyl]amino}propyl)amino]butyl dihydrogen diphosphate} | |
Systematic IUPAC name O1-{[(2R,3S,4R,5R)-5-(6-Amino-9H-purin-9-yl)-4-hydroxy-3-(phosphonooxy)oxolan-2-yl]methyl} O3-{(3R)-3-hydroxy-2,2-dimethyl-4-oxo-4-[(3-oxo-3-{[2-(propanoylsulfanyl)ethyl]amino}propyl)amino]butyl} dihydrogen diphosphate | |
Other names Propionyl Coenzyme A; Propanoyl Coenzyme A | |
Identifiers | |
3D model (JSmol) | |
ChEBI | |
ChemSpider | |
ECHA InfoCard | 100.005.698 |
MeSH | propionyl-coenzyme+A |
PubChem CID | |
UNII | |
CompTox Dashboard (EPA) | |
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Properties | |
C24H40N7O17P3S | |
Molar mass | 823.60 g/mol |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Propionyl-CoA is a coenzyme A derivative of propionic acid. It is composed of a 24 total carbon chain (without the coenzyme, it is a 3 carbon structure) and its production and metabolic fate depend on which organism it is present in. [1] Several different pathways can lead to its production, such as through the catabolism of specific amino acids or the oxidation of odd-chain fatty acids. [2] It later can be broken down by propionyl-CoA carboxylase or through the methylcitrate cycle. [3] In different organisms, however, propionyl-CoA can be sequestered into controlled regions, to alleviate its potential toxicity through accumulation. [4] Genetic deficiencies regarding the production and breakdown of propionyl-CoA also have great clinical and human significance. [5]
There are several different pathways through which propionyl-CoA can be produced:
The metabolic (catabolic fate) of propionyl-CoA depends on what environment it is being synthesized in. Therefore, propionyl-CoA in an anaerobic environment could have a different fate than that in an aerobic organism. The multiple pathways, either catabolism by propionyl-CoA carboxylase or methylcitrate synthase, also depend on the presence of various genes. [7]
Within the citric acid cycle in humans, propionyl-CoA, which interacts with oxaloacetate to form methylcitrate, can also catalyzed into methylmalonyl-CoA through carboxylation by propionyl-CoA carboxylase (PCC). Methylmalonyl-CoA is later transformed to succinyl-CoA to be further used in the tricarboxylic acid cycle. PCC not only catalyzes the carboxylation of propionyl-CoA to methylmalonyl-CoA, but also acts on several different acyl-CoAs. Nevertheless, its highest binding affinity is to propionyl-CoA. It was further shown that propionyl-CoA transformation is inhibited by the absence of several TCA markers, such as glutamate. The mechanism is shown by the figure to the left. [2]
In mammals, propionyl-CoA is converted to (S)-methylmalonyl-CoA by propionyl-CoA carboxylase, a biotin-dependent enzyme also requiring bicarbonate and ATP.
This product is converted to (R)-methylmalonyl-CoA by methylmalonyl-CoA racemase.
(R)-Methylmalonyl-CoA is converted to succinyl-CoA, an intermediate in the tricarboxylic acid cycle, by methylmalonyl-CoA mutase, an enzyme requiring
cobalamin to catalyze the carbon-carbon bond migration.
The methylmalonyl-CoA mutase mechanism begins with the cleavage of the bond between the 5' CH
2- of 5'-deoxyadenosyl and the cobalt, which is in its 3+ oxidation state (III), which produces a 5'-deoxyadenosyl radical and cobalamin in the reduced Co(II) oxidation state.
Next, this radical abstracts a hydrogen atom from the methyl group of methylmalonyl-CoA, which generates a methylmalonyl-CoA radical. It is believed that this radical forms a carbon-cobalt bond to the coenzyme, which is then followed by the rearrangement of the substrate's carbon skeleton, thus producing a succinyl-CoA radical. This radical then goes on to abstract a hydrogen from the previously produced 5'-deoxyadenosine, again creating a deoxyadenosyl radical, which attacks the coenzyme to reform the initial complex.
A defect in methylmalonyl-CoA mutase enzyme results in methylmalonic aciduria, a dangerous disorder that causes a lowering of blood pH. [8]
Propionyl-CoA accumulation can prove toxic to different organisms. Since different cycles have been proposed regarding how propionyl-CoA is transformed into pyruvate, one studied mechanism is the methylcitrate cycle. The initial reaction is beta-oxidation to form the propionyl-CoA which is further broken down by the cycle. This pathway involves the enzymes both related to the methylcitrate cycle as well as the citric acid cycle. These all contribute to the overall reaction to detoxify the bacteria from harmful propionyl-CoA. It is also attributed as a resulting pathway due to the catabolism of fatty acids in mycobacteria. [3] In order to proceed, the prpC gene codes for methylcitrate synthase, and if not present, the methylcitrate cycle will not occur. Instead, catabolism proceeds through propionyl-CoA carboxylase. [7] This mechanism is shown below to the left along with the participating reactants, products, intermediates, and enzymes.
The oxidation of propionyl-CoA to form pyruvate is influenced by its necessity in Mycobacterium tuberculosis . Accumulation of propionyl-CoA can lead to toxic effects. In Mycobacterium tuberculosis, it has been suggested that the metabolism of propionyl-CoA is involved in cell wall biogenesis. A lack of such catabolism would therefore increase the susceptibility of the cell to various toxins, particularly to macrophage antimicrobial mechanisms. Another hypothesis regarding the fate of propionyl-CoA, in M. tuberculosisis, is that since propionyl-CoA is produced by beta odd chain fatty acid catabolism, the methylcitrate cycle is activated subsequently to negate any potential toxicity, acting as a buffering mechanism. [11]
Propionyl-CoA has can have many adverse and toxic affects on different species, including bacterium. For example, inhibition of pyruvate dehydrogenase by an accumulation of propionyl-CoA in Rhodobacter sphaeroides can prove deadly. Furthermore, as with E. coli, an influx of propionyl-CoA in Myobacterial species can result in toxicity if not dealt with immediately. This toxicity is caused by a pathway involving the lipids that form the bacterial cell wall. Using esterification of long-chain fatty acids, excess propionyl-CoA can be sequestered and stored in the lipid, triacylglycerol (TAG), leading to regulation of elevated propionyl-CoA levels. Such a process of methyl branching of the fatty acids causes them to act as sinks for accumulating propion [4]
In an investigation performed by Luo et al., Escherichia coli strains were utilized to examine how the metabolism of propionyl-CoA could potentially lead to the production of 3-hydroxypropionic acid (3-HP). It was shown that a mutation in a key gene involved in the pathway, succinate CoA-transferase, led to a significant increase in 3-HP. [7] However, this is still a developing field and information on this topic is limited. [12]
Amino acid metabolism in plants has been deemed a controversial topic, due to the lack of concrete evidence for any particular pathway. However, it has been suggested that enzymes related to the production and use of propionyl-CoA are involved. Associated with this is the metabolism of isobutyryl-CoA. These two molecules are deemed to be intermediates in valine metabolism. As propionate consists in the form of propionyl-CoA, it was discovered that propionyl-CoA is converted to β-hydroxypropionate through a peroxisomal enzymatic β-oxidation pathway. Nevertheless, in the plant Arabidopsis , key enzymes in the conversion of valine to propionyl-CoA were not observed. Through different experiments performed by Lucas et al., it has been suggested that in plants, through peroxisomal enzymes, propionyl-CoA (and isobutyryl-CoA) are involved in the metabolism of many different substrates (currently being evaluated for identity), and not just valine. [13]
Propionyl-CoA production through the catabolism of fatty acids is also associated with thioesterifcation. In a study concerning Aspergillus nidulans , it was found that with the inhibition of a methylcitrate synthase gene, mcsA, of the pathway described above, production of distinct polyketides was inhibited as well. Therefore, the utilization of propionyl-CoA through the methylcitrate cycle decreases its concentration, while subsequently increasing the concentration of polyketides. A polyketide is a structure commonly found in fungi that is made of acetyl- and malonyl-CoAs, providing a product with alternating carbonyl groups and methylene groups. Polyketides and polyketide derivatives are often highly structurally complex, and several are highly toxic. This has led to research on limiting polyketide toxicity to crops in agriculture through phytopathogenic fungi. [14]
Propionyl-CoA is also a substrate for post-translational modification of proteins by reacting with lysine residues on proteins, a reaction called protein propionylation. [15] [16] Due to structural similarities of Acetyl-CoA and Propionyl-CoA, propionylation reaction are thought to use many of the same enzymes used for protein acetylation. [16] Although functional consequences of protein propionylation are currently not completely understood, in vitro propionylation of the Propionyl-CoA Synthetase enzyme controls its activity. [17]
Similar to how plant peroxisomal enzymes bind propionyl-CoA and isobutyryl-CoA, Gen5, an acetyltransferase in humans, binds to propionyl-CoA and butyryl-CoA. These specifically bind to the catalytic domain of Gen5L2. This conserved acetyltransferase is responsible for the regulation of transcription by lysine acetylation of the histone N-terminal tails. This function of acetylation has a much higher reaction rate than propionylation or butyrylation. Because of the structure of propionyl-CoA, Gen5 distinguishes between different acyl-CoA molecules. In fact, it was found that the propyl group of butyrl-CoA cannot bind due to lack of stereospecificity to the active binding site of Gen5 due to the unsaturated acyl chains. On the other hand, the third carbon of propionyl-CoA can fit into the active site of Gen5 with the correct orientation. [18]
In the neonatal developmental stages, propionic acidemia, which is a medical issue defined as the lack of propionyl-CoA carboxylase, can cause impairment, mental disability, and numerous other issues. This is caused by an accumulation of propionyl-CoA because it cannot be converted to methylmalonyl-CoA. Newborns are tested for elevated propionylcarnitine. Further ways of diagnosing this disease include urine samples. Medications used help to reverse and prevent recurring symptoms include using supplements to decrease propionate production. [5]
Coenzyme A (CoA, SHCoA, CoASH) is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids, and the oxidation of pyruvate in the citric acid cycle. All genomes sequenced to date encode enzymes that use coenzyme A as a substrate, and around 4% of cellular enzymes use it (or a thioester) as a substrate. In humans, CoA biosynthesis requires cysteine, pantothenate (vitamin B5), and adenosine triphosphate (ATP).
Acetyl-CoA is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle to be oxidized for energy production.
Propionic acid is a naturally occurring carboxylic acid with chemical formula CH
3CH
2CO
2H. It is a liquid with a pungent and unpleasant smell somewhat resembling body odor. The anion CH
3CH
2CO−
2 as well as the salts and esters of propionic acid are known as propionates or propanoates.
Propionic acidemia, also known as propionic aciduria or propionyl-CoA carboxylase deficiency, is a rare autosomal recessive metabolic disorder, classified as a branched-chain organic acidemia.
Succinyl-coenzyme A, abbreviated as succinyl-CoA or SucCoA, is a thioester of succinic acid and coenzyme A.
Fatty acid metabolism consists of various metabolic processes involving or closely related to fatty acids, a family of molecules classified within the lipid macronutrient category. These processes can mainly be divided into (1) catabolic processes that generate energy and (2) anabolic processes where they serve as building blocks for other compounds.
In biochemistry and metabolism, beta oxidation (also β-oxidation) is the catabolic process by which fatty acid molecules are broken down in the cytosol in prokaryotes and in the mitochondria in eukaryotes to generate acetyl-CoA. Acetyl-CoA enters the citric acid cycle, generating NADH and FADH2, which are electron carriers used in the electron transport chain. It is named as such because the beta carbon of the fatty acid chain undergoes oxidation and is converted to a carbonyl group to start the cycle all over again. Beta-oxidation is primarily facilitated by the mitochondrial trifunctional protein, an enzyme complex associated with the inner mitochondrial membrane, although very long chain fatty acids are oxidized in peroxisomes.
Malonyl-CoA is a coenzyme A derivative of malonic acid.
Calcium propanoate or calcium propionate has the formula Ca(C2H5COO)2. It is the calcium salt of propanoic acid.
Methylmalonyl-CoA mutase is a mitochondrial homodimer apoenzyme that focuses on the catalysis of methylmalonyl CoA to succinyl CoA. The enzyme is bound to adenosylcobalamin, a hormonal derivative of vitamin B12 in order to function. Methylmalonyl-CoA mutase deficiency is caused by genetic defect in the MUT gene responsible for encoding the enzyme. Deficiency in this enzyme accounts for 60% of the cases of methylmalonic acidemia.
Propionyl-CoA carboxylase (EC 6.4.1.3, PCC) catalyses the carboxylation reaction of propionyl-CoA in the mitochondrial matrix. PCC has been classified both as a ligase and a lyase. The enzyme is biotin-dependent. The product of the reaction is (S)-methylmalonyl CoA.
Methylcrotonyl CoA carboxylase is a biotin-requiring enzyme located in the mitochondria. MCC uses bicarbonate as a carboxyl group source to catalyze the carboxylation of a carbon adjacent to a carbonyl group performing the fourth step in processing leucine, an essential amino acid.
Methylmalonyl-CoA is the thioester consisting of coenzyme A linked to methylmalonic acid. It is an important intermediate in the biosynthesis of succinyl-CoA, which plays an essential role in the tricarboxylic acid cycle. The compound is sometimes referred to as "methylmalyl-CoA".
Fatty acid degradation is the process in which fatty acids are broken down into their metabolites, in the end generating acetyl-CoA, the entry molecule for the citric acid cycle, the main energy supply of living organisms, including bacteria and animals. It includes three major steps:
Thiolases, also known as acetyl-coenzyme A acetyltransferases (ACAT), are enzymes which convert two units of acetyl-CoA to acetoacetyl CoA in the mevalonate pathway.
Methylmalonyl CoA epimerase is an enzyme involved in fatty acid catabolism that is encoded in human by the "MCEE" gene located on chromosome 2. It is routinely and incorrectly labeled as "methylmalonyl-CoA racemase". It is not a racemase because the CoA moiety has 5 other stereocenters.
α-Ketobutyric acid is an organic compound with the formula CH3CH2C(O)CO2H. It is a colorless solid that melts just above room temperature. Its conjugate base α-ketobutyrate is the predominant form found in nature (near neutral pH). It results from the lysis of cystathionine. It is also one of the degradation products of threonine, produced by the catabolism of the amino acid by threonine dehydratase. It is also produced by the degradation of homocysteine and the metabolism of methionine.
The enzyme methylisocitrate lyase catalyzes the chemical reaction
Odd-chain fatty acids are those fatty acids that contain an odd number of carbon atoms. In addition to being classified according to their saturation or unsaturation, fatty acids are also classified according to their odd or even numbers of constituent carbon atoms. With respect to natural abundance, most fatty acids are even chain, e.g. palmitic (C16) and stearic (C18). In terms of physical properties, odd and even fatty acids are similar, generally being colorless, soluble in alcohols, and often somewhat oily. The odd-chain fatty acids are biosynthesized and metabolized slightly differently from the even-chained relatives. In addition to the usual C12-C22 long chain fatty acids, some very long chain fatty acids (VLCFAs) are also known. Some of these VLCFAs are also of the odd-chain variety.
The methylcitrate cycle, or the MCC, is the mechanism by which propionyl-CoA is formed, generated by β-oxidation of odd-chain fatty acids, and broken down to its final products, succinate and pyruvate. The methylcitrate cycle is closely related to both the citric acid cycle and the glyoxylate cycle, in that they share substrates, enzymes and products. The methylcitrate cycle functions overall to detoxify bacteria of toxic propionyl-CoA, and plays an essential role in propionate metabolism in bacteria. Incomplete propionyl-CoA metabolism may lead to the buildup of toxic metabolites in bacteria, and thus the function of the methylcitrate cycle is an important biological process.