Allen sandbox 1
is an enzyme that catalyzes the reversible dehydration reaction of 2-phosphoglycerate (2PG) into phosphophenolglycerate (PEP) in the 9th reaction of glycolysis.[1] Glycolysis converts glucose into two 3-carbon molecules called pyruvate. The energy released during glycolysis is used to make ATP.[2] Enolase is expressed abundantly in most cells and has been proven useful as a model to study mechanisms of enzyme action and structural analysis, especially for those enzymes involved in glycolysis [3].
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| 1one, resolution 1.80Å () | |||||||||
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| Ligands: | , | ||||||||
| Non-Standard Residues: | |||||||||
| Activity: | Phosphopyruvate hydratase, with EC number 4.2.1.11 | ||||||||
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| Resources: | FirstGlance, OCA, PDBsum, RCSB | ||||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||||
StructureStructure
The of enolase contains both alpha helices and beta sheets. The beta sheets are mainly parallel[4]. As shown in the figure, enolase has about 36 alpha helices and 22 beta sheets (18 alpha helices and 11 beta sheets per domain), resulting in a molecular weight of 82,000-100,000 Daltons. Enolase consists of two domains paired together in antiparallel orientation.
Structural Clasification of Proteins (SCOP)[5]
Enolase is in the alpha and beta proteins class and has a fold of TIM beta/alpha-barrel. It comes from the Superfamily on Enolase C-terminal domain-like and is in the enolase family.
MechanismMechanism
The of enolase includes the residues Lys 345, Lys 396, Glu 168, Glu 211, and His 159. Enolase forms a complex with two at its active site. The mechanism of enolase follows 3 steps: Step 1: The substrate, 2PG, binds to the two . The carboxyl group coordinates with the two magnesium ions, which stabilizes the negative charge on the oxygen atom and removes charge from the alpha hydrogen, making it a better leaving group.
Step 2: Lys 345 then deprotonates the alpha hydrogen, a reaction which is stabilized by resonance between the carboxyl oxygens and the two Mg ions, in addition to the stabilizing effect of Glu 211 bonded to the hydroxyl group. This creates a carbanion intermediate.
Step 3: An electron transfer reaction then occurs from the C'1 carboxyl oxygen to form a ketone. This removes electrons from the alkene bond between C'1 and C'2 to create an alkene between C'2 and C'3 instead. This allows the C'3 hydroxyl group to deprotonate Glu 211, resulting in the ejection of a water molecule and the product PEP. PEP then continues in glycolysis to create pyruvate.
Additionally, this mechanism can be inhibited by addition of Fluoride ions, which bond to Mg 2+, thus blocking the substrate (2PG) from binding to the active site of enolase.[7]
KineticsKinetics
![V vs. [PGA]; PGA is 2PG, the top curve has [Mg2+] of 10^-3 M and the bottom curve has [Mg2+] of 106-2 M](/w/File:Enolase_kinetics.jpeg)
Since Mg2+ is essential for binding the substrate, 2-PG, it is also needed at a specific quantity in order to have a sufficient reaction velocity. This graph shows the Velocity vs. [PGA], in which PGA is 2-PG, at two different concentrations of Mg2+. The upper curve (Mg2+ concentration of 10^-3 M) attains a greater Vmax than the lower curve (Mg2+ concentration of 10^-2 M)[9]. The Km of upper curve is also larger than the lower curve, which means a greater concentration of substrate is needed to attain the higher Vmax. Therefore, the lower Mg2+ concentration (upper curve) is more desirable. Clearly, upon addition of Mg2+, the reaction velocity is lowered to sub-optimum levels, thereby inhibiting the activity of enolase.
RegulationRegulation
Enolase is found on the surface of a variety of eukaryotic cells as a strong plamingoen-binding receptor and on the surface of hematopietic cells such as monocytes, T cells and B cells, neuronal cells and endothelial cells. Enolase in muscle cells can bind other glycolytic enzymes, such as phosphoglycerate mutase, muscle creatine kinase, pyruvate kinase, and muscle troponin, with high affinity. This suggests that enolase helps facilitate muscle contraction by creating a functional glycolytic segment in the muscle where ATP production occurs. Myc-binding protein (MBP-1) is similar to the α-enolse structure and is found in the nucleus as a DNA-binding protein[10]. Enolase is regulated by the concentration of Mg2+ and the previous steps of glycolysis.
Additional ResourcesAdditional Resources
For additional information, see: Carbohydrate Metabolism
ReferencesReferences
- ↑ Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry: Life at the Molecular Level. 3rd ed. Hoboken, NJ: John Wiley & Sons, Inc., 2008.
- ↑ Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry: Life at the Molecular Level. 3rd ed. Hoboken, NJ: John Wiley & Sons, Inc., 2008.
- ↑ Pancholi, V. "Multifunctional a-Enolase: Its Role in Diseases." CMLS, Cellular and Molecular Life Sciences 58 (2001): 902-20.
- ↑ The scop authors. Structural Classification of Proteins. “Protein: Enolase from Baker's yeast (Saccharomyces cerevisiae). 2009. 2/26 2010. [<http://scop.mrc-lmb.cam.ac.uk/scop/data/scop.b.d.b.bc.b.b.html>.]
- ↑ The scop authors. Structural Classification of Proteins. “Protein: Enolase from Baker's yeast (Saccharomyces cerevisiae). 2009. 2/26 2010. [<http://scop.mrc-lmb.cam.ac.uk/scop/data/scop.b.d.b.bc.b.b.html>.]
- ↑ Nguyen, Tram, and Katelyn Thompson. "Mechanism of Enolase Converting 2-Phosphoglycerate to Phosphoenolpyruvate." ChemDraw 10.0: Public Domain, 2008. [1].
- ↑ Voet, Donald, Judith G. Voet, and Charlotte W. Pratt. Fundamentals of Biochemistry: Life at the Molecular Level. 3rd ed. Hoboken, NJ: John Wiley & Sons, Inc., 2008.
- ↑ Westhead, E. W., and BO G. Malmstrom. "The Chemical Kinetics of the Enolase Reaction with Special References to the Use of Mixed Solvents." The Journal of Biological Chemistry 228 (1957): 655-71.
- ↑ Westhead, E. W., and BO G. Malmstrom. "The Chemical Kinetics of the Enolase Reaction with Special References to the Use of Mixed Solvents." The Journal of Biological Chemistry 228 (1957): 655-71.
- ↑ Pancholi, V. "Multifunctional a-Enolase: Its Role in Diseases." CMLS, Cellular and Molecular Life Sciences 58 (2001): 902-20.