Sandbox Reserved 455

This Sandbox is Reserved from 13/03/2012, through 01/06/2012 for use in the course "Proteins and Molecular Mechanisms" taught by Robert B. Rose at the North Carolina State University, Raleigh, NC USA. This reservation includes Sandbox Reserved 451 through Sandbox Reserved 500.

To get started: Click the edit this page tab at the top. Save the page after each step, then edit it again. Click the 3D button (when editing, above the wikitext box) to insert Jmol. show the Scene authoring tools, create a molecular scene, and save it. Copy the green link into the page. Add a description of your scene. Use the buttons above the wikitext box for bold, italics, links, headlines, etc. More help: Help:Editing For more help, look at this link: http://www.proteopedia.org/wiki/index.php/Help:Getting_Started_in_Proteopedia Neuron Specific Enolase Enolase 2Neuron Specific Enolase Enolase 2 IntroductionIntroduction spinqualitylabelsall models RSCB-Protein Data Bank: Crystal Structure of Human Neuron Specific Enolase at 1.8 angstrom Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image Neuron Specific Enolase (NSE) is one of the five isozymes (isoenzyme) of the glycolysis enzyme enolase. An enolase falls under the category of lyase, which is an enzyme that catalyzes the breaking of various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond or a new ring structure. It is also known as a metalloenzyme, which means it contains a metal ion bound to the protein with one labile coordination site. Enolase is present in all tissues and organisms capable of glycolysis or fermentation. It is the ninth and penultimate step of glycolysis, converting 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP). Biological Assembly Image for 1PDY Lobster Enolase Enolase has three subunits (α, β, and γ) and all of these subunits are usually found in vertebrates. Enolase α is ubiquitous, found in all cells, enolase β is muscle-specific, and the γ isozyme is found only in neurons. The subunits can combine in pairs (αα, αβ, αγ, ββ, and γγ) and form the five different isozymes of enolase. It is more common to find the homodimers (αα, ββ, and γγ) in adult human cells. The αα is called enolase 1, the ββ enolase 3, and the γγ enolase 2. Each homodimer still holds their original function: Enolase 1 is non-neuronal enolase (NNE), which is found in a variety of tissues, including liver, brain, kidney, spleen, adipose, enolase 3 is muscle specific enolase (MSE), and enolase 2 neuron-specific enolase (NSE). NSE (also called Gamma-Enolase) is the most abundant form of the glycolytic enolase found in adult neurons and is thought to serve as a growth factor in neurons. NSE is useful in studying neuronal differentiation and is, therefore, a valuable tool for visualizing the entire neuron and endocrine systems. NSE is mainly found in mammals, and it functions as a Phosphopyruvate dehydratase. It is specifically a hydro-lyase, which cleave carbon-oxygen bonds. In humans, NSE is encoded by the ENO2 gene. The systematic name of this enzyme class is 2-phospho-D-glycerate hydro-lyase (phosphoenolpyruvate-forming). Other names in common use include nervous-system specific enolase, phosphoenolpyruvate hydrates, 2-phosphoglycerate dehydrates, 2-phosphoglyceric dehydrates, gamma-enolase, and 2-phospho-D-glycerate hydro-lyase. The only inhibitor known for the enzyme so far is Phosphonoacetohydroxamate StructureStructure NSE, as mentioned in the introduction, is composed of the two gamma, γ, subunits of enolase. NSE functions in neurons, but it still performs the duties of glycolytic enolase. Each subunit is composed of two domains, a smaller N-terminal Domain and a larger C-terminal domain. For enolase in general, the smaller N-terminal domain consists of three α-helices and four β-sheets. The larger C-terminal domain starts with two β-sheets followed by two α-helices and ends with a barrel composed of alternating β-sheets and α-helices arranged so that the β-beta sheets are surrounded by the α-helices. The enzyme’s compact, globular structure results from significant interactions between these two domains. The Jmol image (1te6) to the right was referenced from the RSCB Protein Data Bank where human neuron-specific enolase had been expressed with a C-terminal His-tag in Escherichia coli. The enzyme has been purified, crystallized and its crystal structure determined. In the crystals the enzyme forms the asymmetric complex NSE x Mg2 x SO4/NSE x Mg x Cl, where "/" separates the dimer subunits. The that contains the sulfate (or ) ion and two ions is in the closed conformation observed in enolase complexes with the substrate or its analogues; the other is in the open conformation observed in enolase subunits without bound substrate or analogues. This indicates negative cooperativity for ligand binding between subunits. Other ligands that are present in NSE are and (2-amino-2-hydroxymethy;-propane-1,3-diol). There are three active residues in the ; ASP 317, GLU 292, ASP 244. An integral part of enolase are two Mg2+ cofactors in the active site, which serve to stabilize negative charges in the substrate. A description of how magnesium plays a role in the ninth step of glycolysis is explained below in the Mechanism section of this article. Biological Assembly Image for 1TE6 Enolase 2 MechanismMechanism The overall glycolytic mechanism for converting 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP) is proposed to be an E1 elimination reaction involving a carbanion intermediate. The following detailed mechanism is based on studies of crystal structure and kinetics. When the substrate, 2-PG, binds to 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 Lys 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. As said before, the inhibitor known for stopping NSE's enzymatic process is Phosphonoacetohydroxamate Mechanism for conversion of 2PG to PEP MedicineMedicine Neuron-specific enolase is a substance that has been detected in patients with certain tumors, namely: neuroblastoma, small cell lung cancer, medullary thyroid cancer, carcinoid tumors, pancreatic endocrine tumors, and melanoma. Studies of NSE as a tumor marker have concentrated primarily on patients with neuroblastoma and small cell lung cancer. Measurement of NSE levels in patients with these two diseases can provide information about the extent of the disease and the patient's prognosis (outlook), as well as about the patient's response to treatment. As mentioned earlier, NSE is a valuable tool for visualizing the entire neuron and endocrine systems. Detection of NSE with antibodies can be used to identify neuronal cells and cells with neuroendocrine differentiation. Serum levels of NSE have been associated with such disease states as Alzheimer's, Huntington's Chorea, neuroblastoma, head trauma, and neuroendocrine malignancies. ReferencesReferences