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{{STRUCTURE_1l8a | PDB=1l8a | SCENE= }}Pyruvate dehydrogenase (E1) is one of three main components of the multienzyme complex pyruvate dehydrogenase. It accompanies dihydrolipoyl transacetylase (E2) and dihydrolipoyl dehydrogenase (E3) in comprising this multienzyme complex. The E. coli enzyme complex has a weight of approximately 4600-kD and a diameter of about 300 angstroms. The core of the particle is made of 24 E2 proteins arranged in a cube, which is surrounded by 24 E1 proteins and 12 E3 proteins. Together, these enzymes are responsible for synthesizing acetyl-CoA from pyruvate just prior to entrance into the citric acid cycle. Therefore, pyruvate dehydrogenase contributes to linking the glycolysis metabolic pathway to the citric acid pathway. | |||
{{STRUCTURE_1l8a | PDB=1l8a | SCENE= }}Pyruvate dehydrogenase (E1) is one of three main components of the multienzyme complex pyruvate dehydrogenase. It accompanies dihydrolipoyl transacetylase (E2) and dihydrolipoyl dehydrogenase (E3) in comprising this multienzyme complex. | |||
==Structure== | ==Structure== | ||
Pyruvate dehydrogenase (E1) falls within the class of alpha and beta proteins<ref>Protein: Pyruvate dehydrogenase E1-beta, PdhB, C-terminal domain from Bacillus stearothermophilus. (2009). Retrieved from http://scop.mrc-lmb.cam.ac.uk</ref>, containing <scene name='Kenny_Coggins_Sandbox_1/Secondary_structure/1'>mixed alpha helices and beta sheets</scene>. It is a multimeric protein. Mammalian E1s, including human E1, are heterotetrameric, composed of two α- and two β- subunits<ref>Ciszak EM, Korotchkina LG, Dominiak PM, Sidhu S, Patel MS (June 2003). "Structural basis for flip-flop action of thiamin pyrophosphate-dependent enzymes revealed by human pyruvate dehydrogenase". J. Biol. Chem. 278 (23): 21240–6</ref>. E1 from E. coli is, however, a homodimer with a molecular weight of 99474 containing α/β folds. It has two catalytic sites located at the interface between subunits. Each polypeptide chain consists of 886 residues<ref name="PMID">PMID:11955070</ref>. The structure shown is the E. coli E1 pyruvate dehydrogenase component, PDB code | |||
[[1l8a]]<ref>Jmol: an open-source Java viewer for chemical structures in 3D. http://www.jmol.org/</ref>. | [[1l8a]]<ref>Jmol: an open-source Java viewer for chemical structures in 3D. http://www.jmol.org/</ref>. | ||
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Pyruvate + TPP ==> Hydroxyethyl-TPP + CO2 | Pyruvate + TPP ==> Hydroxyethyl-TPP + CO2 | ||
The enzyme requires <scene name='Kenny_Coggins_Sandbox_1/Thdp/5'>TPP and | The enzyme requires <scene name='Kenny_Coggins_Sandbox_1/Thdp/5'>TPP and Mg2+</scene> as cofactors for catalysis. [[Image:Thiamine pyrophosphate.png|thumb|left|alt=Thiamine pyrophosphate.|Thiamine pyrophosphate (TPP) E1 cofactor.]] In this reaction, the ylide form of TPP attacks the electrophilic carbonyl group of pyruvate. This reflects the ability of TPP’s thiazolium ring, which primarily interacts with <scene name='Kenny_Coggins_Sandbox_1/Ile569_asp521/5'>Ile569 and Asp521</scene>, to add to carbonyl groups. Decarboxylation of the resulting alkoxide yields an enol complex. This enol resonates to form the ylide form of hydroxyethyl-TPP<ref name="book">Voet, D., Voet, J.G., and Pratt, C.W. (2008). Fundamentals of biochemistry. Hoboken, NJ: John Wiley and Sons, Inc.</ref>. During this reaction, the catalytic Mg2+ ion coordinates octahedrally with three protein ligands: <scene name='Kenny_Coggins_Sandbox_1/Asp230_and_asn260/2'>Asp230 and Asn 260</scene>, which bind TPP, and <scene name='Kenny_Coggins_Sandbox_1/Glu262/2'>Glu262</scene><ref name="PMID" />. | ||
The second E1-catalyzed reaction is the transfer of the hydroxyethyl group to the lipoamide group of the next enzyme, dihydrolipoyltransacetylase (E2). The E2 lipoamide group consisting of lipoic acid linked to the amide group of a Lys residue. Lipoic acid contains a reactive cyclic disulfide that is reversibly reduced to give dihydrolipoamide. The ylide form of the hydroxyethyl group of the hydroxyethyl-TPP complex attacks this disulfide bond. TPP is then eliminated as it detaches with E1 and subsequently binds to the next pyruvate molecule<ref name="book" />. | The second E1-catalyzed reaction is the transfer of the hydroxyethyl group to the lipoamide group of the next enzyme, dihydrolipoyltransacetylase (E2). The E2 lipoamide group consisting of lipoic acid linked to the amide group of a Lys residue. Lipoic acid contains a reactive cyclic disulfide that is reversibly reduced to give dihydrolipoamide. The ylide form of the hydroxyethyl group of the hydroxyethyl-TPP complex attacks this disulfide bond. TPP is then eliminated as it detaches with E1 and subsequently binds to the next pyruvate molecule<ref name="book" />. | ||
E1-Hydroxyethyl-TPP + E2-Lipoamide ==> E1-TPP + Acetyl-dihydrolipoamide-E2 | E1-Hydroxyethyl-TPP + E2-Lipoamide ==> E1-TPP + Acetyl-dihydrolipoamide-E2 | ||
The overall mechanism is shown as following: | |||
[[Image:PyruvateDehydrgenaseMech.gif]] | |||
==Regulation== | ==Regulation== | ||
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These two compounds also activate the pyruvate dehydrogenase kinase associated with the enzyme complex<ref name="book" />. This results in phosphorylation of three different E1 serine residues (Ser 203, Ser 264, Ser 271) in human E1 and enzyme inactivation<ref>PMID:11092882</ref>. Enzyme regulation through phosphorylation by pyruvate dehydrogenase kinase and dephosphorylation pyruvate dehydrogenase phosphatase has been implicated as a target for treating cancer, heart ischemia, and diabetes<ref>PMID:17310282</ref>. | These two compounds also activate the pyruvate dehydrogenase kinase associated with the enzyme complex<ref name="book" />. This results in phosphorylation of three different E1 serine residues (Ser 203, Ser 264, Ser 271) in human E1 and enzyme inactivation<ref>PMID:11092882</ref>. Enzyme regulation through phosphorylation by pyruvate dehydrogenase kinase and dephosphorylation pyruvate dehydrogenase phosphatase has been implicated as a target for treating cancer, heart ischemia, and diabetes<ref>PMID:17310282</ref>. | ||
[[Image:400px-1400x1048_pdh_regulation.png]] | |||
==Kinetics== | ==Kinetics== | ||
E. coli pyruvate dehydrogenase binding constant and maximum velocity values have been reported as Km = 0.3 mM and Vmax = 5,500 kat/mol (37 degrees C, pH = 7.6, 5 microM pyruvate, and 3 mg/L protein). The multienzyme complex exhibits postive cooperative binding (Hill constant = 1.9)<ref>Bisswanger, H. Substrate specificity of the pyruvate dehydrogenase complex from escherichia coli. J Biol Chem. 1981. Jan 25;256(2):815-822.</ref>. | E. coli pyruvate dehydrogenase binding constant and maximum velocity values have been reported as Km = 0.3 mM and Vmax = 5,500 kat/mol (37 degrees C, pH = 7.6, 5 microM pyruvate, and 3 mg/L protein). The multienzyme complex exhibits postive cooperative binding (Hill constant = 1.9)<ref>Bisswanger, H. Substrate specificity of the pyruvate dehydrogenase complex from escherichia coli. J Biol Chem. 1981. Jan 25;256(2):815-822.</ref>. | ||
==Medical Implications== | |||
Pyruvate dehydrogenase is an autoantigen recognized in primary biliary cirrhosis. These antibodies appear to recognize oxidized protein that has resulted from inflammatory immune responses. Some of these inflammatory responses are explained by gluten sensitivity<ref> Leung PS, Rossaro L, Davis PA, et al. (2007). "Antimitochondrial antibodies in acute liver failure: Implications for primary biliary cirrhosis". Hepatology 46 (5): 1436</ref>. Other mitochondrial autoantigens include oxoglutarate dehydrogenase and branched-chain alpha-keto acid dehydrogenase complex, which are antigens recognized by anti-mitochondrial antibodies. | |||
Pyruvate dehydrogenase (PDH) deficiency is a congenital degenerative metabolic disease resulting from a mutation of the pyruvate dehydrogenase complex (PDC) located on the X chromosome. Although defects have been identified in all 3 enzymes of the complex, the E1-α subunit is predominantly the culprit. Malfunction of the citric acid cycle due to PDH deficiency deprives the body of energy and leads to an abnormal buildup of lactate. PDH deficiency is a common cause of lactic acidosis in newborns and often presents with severe lethargy, poor feeding, tachypnea, and cases of death have occurred<ref>Frye, Richard E., and Paul J. Benke. "Pyruvate Dehydrogenase Complex Deficiency." EMedicine. 11 Dec. 2007. WebMD. 14 Dec. 2008 </ref>. | |||
==References== | |||
<references/> | <references/> | ||