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In enzymology, a phosphoenolpyruvate mutase () is an enzyme that catalyzes the chemical reaction :phosphoenolpyruvate 3-phosphonopyruvate File:PEP to PPR.png Hence, this enzyme has one substrate, phosphoenolpyruvate (PEP), and one product, 3-phosphonopyruvate (PPR), which are structural isomers. This enzyme belongs to the family of isomerases, specifically the phosphotransferases (phosphomutases), which transfer phosphate groups within a molecule. The systematic name of this enzyme class is phosphoenolpyruvate 2,3-phosphonomutase. Other names in common use include phosphoenolpyruvate-phosphonopyruvate phosphomutase, PEP phosphomutase, phosphoenolpyruvate phosphomutase, PEPPM, and PEP phosphomutase. This enzyme participates in aminophosphonate metabolism. Phosphoenolpyruvate mutase was discovered in 1988. ==Structural studies== As of late 2007, 6 structures have been solved for this class of enzymes, all by the Herzberg group () at the University of Maryland using PEPPM from the blue mussel, ''Mytilus edulis''. The first structure (PDB accession code ) was solved in 1999 and featured a magnesium oxalate inhibitor. This structure identified the enzyme as consisting of identical beta barrel subunits (exhibiting the TIM barrel fold, which consists of eight parallel beta strands). Dimerization was observed in which a helix from each subunit interacts with the other subunit's barrel; the authors called this feature "helix swapping." The dimers can dimerize as well to form a homotetrameric enzyme. A double phosphoryl transfer mechanism was proposed on the basis of this study: this would involve breakage of PEP's phosphorus-oxygen bond to form a phosphoenzyme intermediate, followed by transfer of the phosphoryl group from the enzyme to carbon-3, forming PPR. However, more recently, a structure with a sulfopyruvate inhibitor, which is a closer substrate analogue, was solved (); this study supported instead a dissociative mechanism. A notable feature of these structures was the shielding of the active site from solvent; it was proposed that a significant conformational change takes place on binding to allow this, moving the protein from an "open" to a "closed" state, and this was supported by several crystal structures in the open state. Three of these were of the wild type: the apoenzyme in , the enzyme plus its magnesium ion cofactor in , and the enzyme at high ionic strength in . A mutant (D58A, in one of the active-site loops) was crystallized as an apoenzyme also (). From these structures, an active-site "gating" loop (residues 115-133) that shields the substrate from solvent in the closed conformation was identified. The two conformations, taken from the crystal structures 1M1B (closed) and 1S2T (open), are docked into each other in the images below; they differ negligibly except in the gating loop, which is colored purple for the closed conformation and blue for the open conformation. In the active-site closeup (left), several sidechains (cyan) that have been identified as important in catalysis are included as well; the overview (right) illustrates the distinctive helix-swapping fold. The images are still shots from ribbon kinemages. Both of these structures were crystallized as dimers. In chain A (used for the active-site closeup), helices are red while loops (other than the gating loop) are white and beta strands are green; in chain B, helices are yellow, beta strands are olive, and loops are gray; these colors are the same for the closed and open structures. Magnesium ions are gray and the sulfopyruvate ligands are pink; both are from the closed structure (though the enzyme has also been crystallized with only magnesium bound, and it adopted an open conformation). File:activesite PEPPM.jpg File:overview PEPPM.jpg The structure of PEPPM is very similar to that of methylisocitrate lyase, an enzyme involved in propanoate metabolism whose substrate is also a low-molecular weight carboxylic acid—the beta-barrel structure as well as the active site layout and multimerization geometry are the same. Isocitrate lyase is also quite similar, though each subunit has a second, smaller beta domain in addition to the main beta barrel. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Phosphoenolpyruvate mutase」の詳細全文を読む スポンサード リンク
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