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Enolase

Enzyme Enolase
PDB Code PDB 2ONE
Organism Yeast
Complexed molecules 2-phosphoglycerate and phosphoenolpyruvate

Enolase, also known as phosphopyruvate dehydratase, is a metalloenzyme responsible for the catalysis of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP), the ninth and penultimate step of glycolysis. The Protein Data Bank ( PDB) is a repository for 3-D structural data of Proteins and Nucleic acids These data typically obtained by X-ray crystallography Yeasts are a growth form of eukaryotic Microorganisms classified in the kingdom Fungi, with about 1500 Species currently described Phosphoenolpyruvate (synonyms phosphoenolpyruvic acid, PEP) is an important Chemical compound in Biochemistry. In Biochemistry, a metalloprotein is a generic term for a Protein that contains a Metal cofactor. Phosphoenolpyruvate (synonyms phosphoenolpyruvic acid, PEP) is an important Chemical compound in Biochemistry. See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized Enolase can also catalyze the reverse reaction, depending on environmental concentrations of substrates. [1] The optimum pH for this enzyme is 6. 5. [2] Enolase is present in all tissues and organisms capable of glycolysis or fermentation. The enzyme was discovered by Lohmann and Meyerhof in 1934, and has since been isolated from a variety of sources including human muscle and erythrocytes. Red blood cells are the most common type of Blood cell and the Vertebrate body's principal means of delivering Oxygen to the body tissues via the Blood [2] There are three subunits of enolase, α, β, and γ, which can combine to form five different isoenzymes: αα, αβ, αγ, ββ, and γγ. Isozymes (also known as isoenzymes) are Enzymes that differ in amino acid sequence but catalyze the same chemical reaction [1],[3] Three of these isoenzymes are more commonly found in adult human cells than the others:

Identifiers
Symbol ENO (1, 2, 3)
Entrez 2023, 2026, 2027
HUGO ENO1, ENO2, ENO3
PDB 1ONE, 2ONE
EC Number 4.2.1.11

Contents

Structure

Enolase has a molecular weight of 82,000-100,000 Daltons depending on the isoform. [1],[2] In human alpha enolase, the two subunits are antiparallel in orientation so that Glu20 of one subunit forms an ionic bond with Arg414 of the other subunit. Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its Arginine (abbreviated as Arg or R) is an α- Amino acid. The L-form is one of the 20 most common natural amino acids [1] Each subunit has two distinct domains. The smaller N-terminal domain consists of three α-helices and four β-sheets. A common motif in the Secondary structure of Proteins the alpha helix (α-helix is a right-handed coiled conformation resembling a spring, in which The β sheet (also β-pleated sheet) is the second form of regular Secondary structure in Proteins consisting of beta strands connected laterally [1],[3] The larger C-terminal domain starts with two β-sheets followed by two α-helices and ends with a barrel comprised of alternating β-sheets and α-helices arranged so that the β-beta sheets are surrounded by the α-helices. [1],[3] The enzyme’s compact, globular structure results from significant hydrophobic interactions between these two domains.

Enolase is a highly conserved enzyme with five active-site residues being especially important for activity. When compared to wild-type enolase, a mutant enolase that differs at either the Glu168, Glu211, Lys345, or Lys396 residue has an activity level that is cut by a factor of 105. Lysine (abbreviated as Lys or K) is an α- Amino acid with the Chemical formula HO2CCH(NH2(CH24NH2 [1] Also, changes affecting His159 leave the mutant with only 0. Histidine (abbreviated as His or H) is one of the 20 standard Amino acids present in Proteins In the Nutritional sense in 01% of its catalytic activity. [1] An integral part of enolase are two Mg2+ cofactors in the active site, which serve to stabilize negative charges in the substrate. [1],[3]

3-D depiction of enolase dimer in antiparallel orientation.

Active site of enolase in the middle of the C-terminal domain’s barrel. Depicted are two Mg2+ cofactors and five highly conserved residues imperative for proper catalytic function: His159, Glu168, Glu211, Lys345, Lys396.

Mechanism

Mechanism for conversion of 2PG to PEP.
Mechanism for conversion of 2PG to PEP.

Using isotopic probes, the overall mechanism for converting 2-PG to PEP is proposed to be an Elcb elimination reaction involving a carbanion intermediate. E1cB elimination reaction is a special type of Elimination reaction in Organic chemistry. [4] The following detailed mechanism is based on studies of crystal structure and kinetics. Chemical kinetics, also known as reaction kinetics is the study of rates of chemical processes [1],[5],[6],[7],[8],[8],[10] When the substrate, 2-phosphoglycerate, binds to α-enolase, its carboxyl group coordinates with two magnesium ion cofactors in the active site. This stabilizes the negative charge on the deprotonated oxygen while increasing the acidity of the alpha hydrogen. Enolase’s Lys345 deprotonates the alpha hydrogen, and the resulting negative charge is stabilized by resonance to the carboxylate oxygen and by the magnesium ion cofactors. Following the creation of the carbanion intermediate, the hydroxide on C3 is eliminated as water with the help of Glu211, and PEP is formed.

Additionally, conformational changes occur within the enzyme that aid catalysis. In human α-enolase, the substrate is rotated into position upon binding to the enzyme due to interactions with the two catalytic magnesium ions, Gln167, and Lys396. Glutamine (abbreviated as Gln or Q; the abbreviation Glx or Z represents either glutamate or Glutamic acid) is one of the 20 Movements of loops Ser36 to His43, Ser158 to Gly162, and Asp255 to Asn256 allow Ser39 to coordinate with Mg2+ and close off the active site. Serine (abbreviated as Ser or S) is an Organic compound with the formula H[[oxygen O]]2 CCH NH sub>2CH2OH Glycine (abbreviated as Gly or G) is the Organic compound with the formula NH2CH2COOH Aspartic acid (abbreviated as Asp or D; Asx or B represent either aspartic acid or Asparagine) is an α- Amino acid Asparagine (abbreviated as Asn or N; Asx or B represent either asparagine or Aspartic acid) is one of the 20 most common natural In addition to coordination with the catalytic magnesium ions, the pKa of the substrate’s alpha hydrogen is also lowered due to protonation of the phosphoryl group by His159 and its proximity to Arg374. Arg374 also causes Lys345 in the active site to become deprotonated, which primes Lys345 for its role in the mechanism.

Diagnostic Uses

In recent medical experiments, enolase concentrations have been sampled in an attempt to diagnose certain conditions and their severity. For example, higher concentrations of enolase in cerebrospinal fluid more strongly correlated to low-grade astrocytoma than did other enzymes tested (aldolase, pyruvate kinase, creatine kinase, and lactate dehydrogenase). Cerebrospinal fluid ( CSF) Liquor cerebrospinalis, is a clear Bodily fluid that occupies the Subarachnoid space and the Ventricular system Astrocytomas are primary Central nervous system Tumors that arise primarily in and rarely spread away from the CNS parenchyma contained within the Cranial vault Reaction The reaction with pyruvate kinase pyruvate kinase PEP ----------> pyruvate / \ ADP ATP Creatine kinase (CK also known as creatine phosphokinase (CPK or phosphocreatine kinase, is an Enzyme ( expressed by various tissue types Lactate dehydrogenase ( LDH) is an Enzyme ( present in a wide variety of organisms including plants and animals [11] The same study showed that the fastest rate of tumor growth occurred in patients with the highest levels of CSF enolase. Increased levels of enolase have also been identified in patients who have suffered a recent myocardial infarction or cerebrovascular accident. Myocardial infarction ( MI or AMI for acute myocardial infarction) also known as a heart attack, occurs when the blood supply A stroke is the rapidly developing loss of brain functions due to a disturbance in the blood vessels supplying blood to the brain It has been inferred that levels of CSF neuron-specific enolase, serum NSE, and creatine kinase (type BB) are indicative in the prognostic assessment of cardiac arrest victims. Blood plasma is the Liquid component of Blood, in which the Blood cells are suspended [12] Other studies have focused on the prognostic value of NSE values in cerebrovascular accident victims. [13]

Fluoride Inhibition

Fluoride is a known competitor of enolase’s substrate, 2-PG. Fluoride is the reduced form of Fluorine. Both organic and Inorganic compounds containing the element fluorine are considered fluorides The fluoride is part of a complex with magnesium and phosphate, which binds in the active site instead of 2-PG. [2] As such, drinking water fluoridation provides fluoride at a level which inhibits oral bacteria enolase activity without harming humans. Water fluoridation is the addition of a chemical to increase the concentration of Fluoride Ions in Drinking water with the purpose of reducing the Disruption of the bacteria’s glycolytic pathway, and thus, its normal metabolic functioning prevents dental caries from forming. Dental caries is a disease that damages Tooth structures resulting in what is commonly called tooth decay or cavities which are holes in the teeth [14],[15]

References

  1. Pancholi V. Multifunctional a-enolase: its role in diseases. Cell Mol Life Sci (2001) 58:902-920.
  2. Hoorn RK, Flickweert JP and Staal GE. Purification and properties of enolase of human erythroctyes. Int J Biochem (1974) 5:845-852.
  3. Peshavaria M and Day IN. Molecular structure of the human muscle-specific enolase gene (EN03). Biochemistry (1991) 275:427-433.
  4. Dinovo EC and Boyer PD. Isotopic probes of the enolase reaction mechanism. J Biol Chem (1971) 240:4586-4593.
  5. Poyner RR, Laughlin LT, Sowa GA and Reed GH. Toward identification of acid/base catalysts in the active site of enolase: Comparison of the properties of K345A, E168Q and E211Q variants. Biochemistry (1996) 35:1692–1699.
  6. Reed GH, Poyner RR, Larsen TM, Wedekind JE and Rayment I. Structural and mechanistic studies of enolase. Curr Opin Struct Biol (1996) 6:736–743
  7. Wedekind JE, Reed GH and Rayment I. Octahedral coordination at the high-affinity metal site in enolase: crystallographic analysis of the MgII – enzyme complex from yeast at 1. 9 Å resolution. Biochemistry (1995) 34:4325–4330.
  8. Wedekind JE, Poyner RR, Reed GH and Rayment I. Chelation of serine 39 to Mg2+ latches a gate at the active site of enolase: structure of the bis(Mg2+) complex of yeast enolase and the intermediate analog phosphonoacetohydroxamate at 2. 1-Å resolution. Biochemistry (1994) 33:9333–9342.
  9. Larsen TM, Wedekind JE, Rayment I and Reed GH. A carboxylate oxygen of the substrate bridges the magnesium ions at the active site of enolase: structure of the yeast enzyme complexed with the equilibrium mixture of 2-phosphoglycerate and phosphoenolpyruvate at 1. 8 Å resolution. Biochemistry (1996) 35:4349–4358.
  10. Duquerroy S, Camus C and Janin J. X-ray structure and catalytic mechanism of lobster enolase. Biochemistry (1995) 34:12513–12523.
  11. Royds JA, Timperley WR and Taylor CB. Levels of enolase and other enzymes in the cerebrospinal fluid as indices of pathological change. J Neurol Neurosurg Pyschiatry (1981) 44:1129-1135.
  12. Roine RO, Somer H, Kaste M, Viinikka L and Karonen SL. Neurological outcome after out-of-hospital cardiac arrest. Prediction by cerebrospinal fluid enzyme analysis. Arch Neurol (1989) 46:753-756.
  13. Hay E, Royds JA, Davies-Jones GA, Lewtas NA, Timperley WR and Taylor CB. Cerebrospinal fluid enolase in stroke. J Neurol Neurosurg Psychiatry (1984) 47:724-729.
  14. Centers For Disease Control And Prevention, comp. Populations Receiving Optimally Fluoridated Public Drinking Water --- United States, 2000 Morbidity and Mortality Weekly Report (2002) 51: 144-147.
  15. Hüther, F-J, N. Psarros, H. Duschner. Isolation, characterization, and inhibition kinetics of enolase from Streptococcus rattus FA-1. Infection and Immunity (1990) 58:1043-1047.

External links

 v • d • e 
Glycolysis Metabolic Pathway
Glucose Hexokinase Glucose-6-phosphate Glucose-6-phosphate isomerase Fructose 6-phosphate 6-phosphofructokinase Fructose 1,6-bisphosphate Fructose bisphosphate aldolase Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate Triosephosphate isomerase Glyceraldehyde 3-phosphate Glyceraldehyde-3-phosphate dehydrogenase
ATP ADP ATP ADP NAD+ + Pi NADH + H+
+ 2
NAD+ + Pi NADH + H+
1,3-Bisphosphoglycerate Phosphoglycerate kinase 3-Phosphoglycerate Phosphoglycerate mutase 2-Phosphoglycerate Phosphopyruvate hydratase(Enolase) Phosphoenolpyruvate Pyruvate kinase Pyruvate Pyruvate dehydrogenase Acetyl-CoA
ADP ATP H2O ADP ATP CoA + NAD+ NADH + H+ + CO2
2 2 2 2 2 2
ADP ATP H2O
Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books This article is about the Enzyme Commission codes For the European Commission system for coding chemicals see EC-No. See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized In Biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Variation across species Hexokinases have been found in every organism checked ranging from bacteria, Yeast, and Plants to humans and other Vertebrates Glucose 6-phosphate (also known as Robison ester) is Glucose sugar Phosphorylated on carbon 6 Glucose-6-phosphate isomerase, or phosphoglucose isomerase, is an Enzyme ( that catalyzes the conversion of Glucose-6-phosphate into Fructose-6-phosphate Fructose 6-phosphate (also known as the Neuberg ester) is Fructose sugar Phosphorylated on carbon 6 (ie Phosphofructokinase-1 (PFK-1 is the most important regulatory Enzyme ( of Glycolysis. Fructose 16-phosphate is Fructose sugar Phosphorylated on carbons 1 and 6 (ie Aldolase A is an Enzyme which catalyses one of the Aldol reactions: The substrate, Fructose 16-bisphosphate (F-16-BP is broken down into Dihydroxyacetone phosphate (DHAP is a biochemical compound involved in many reactions from the Calvin cycle in plants to the ether-lipid biosynthesis process in Leishmania Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GADP, GAP or PGAL Triose-phosphate isomerase (TPI or TIM is an Enzyme ( that catalyzes the reversible interconversion of the Triose phosphate Isomers Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GADP, GAP or PGAL Glyceraldehyde 3-phosphate dehydrogenase (abbreviated as GAPDH or less commonly as G3PDH ( is an Enzyme that catalyzes the sixth step of Overview Phosphoglycerate mutase (PGM is an Enzyme that catalyzes step 8 of Glycolysis. In Enzymology, a phosphopyruvate hydratase ( is an Enzyme that catalyzes the Chemical reaction 2-phospho-D-glycerate \rightleftharpoons Phosphoenolpyruvate (synonyms phosphoenolpyruvic acid, PEP) is an important Chemical compound in Biochemistry. Reaction The reaction with pyruvate kinase pyruvate kinase PEP ----------> pyruvate / \ ADP ATP Pyruvic acid (CH3COCO2H is an alpha-keto acid. The Carboxylate Anion of pyruvic acid is known as pyruvate. Pyruvate dehydrogenase (E1 is the first component Enzyme of Pyruvate dehydrogenase complex (PDC Acetyl-CoA is an important molecule in metabolism used in many biochemical reactions Coenzyme A ( CoA, CoASH, or HSCoA) is a Coenzyme, notable for its role in the synthesis and oxidation of Fatty acids
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