- Kinetic, Thermodynamic, and Structural Insight into the Mechanism of Phosphopantetheine Adenylyltransferase from Mycobacterium tuberculosis
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Phosphopantetheine adenylyltransferase (PPAT) catalyzes the penultimate step in the coenzyme A (CoA) biosynthetic pathway, reversibly transferring an adenylyl group from ATP to 4-phosphopantetheine (PhP) to form dephosphocoenzyme A. This reaction sits at the branch point between the de novo pathway and the salvage pathway, and has been shown to be a rate-limiting step in the biosynthesis of CoA. Importantly, bacterial and mammalian PPATs share little sequence homology, making the enzyme a potential target for antibiotic development. A series of steady-state kinetic, product inhibition, and direct binding studies with Mycobacterium tuberculosis PPAT (MtPPAT) was conducted and suggests that the enzyme utilizes a nonrapid-equilibrium random bi-bi mechanism. The kinetic response of MtPPAT to the binding of ATP was observed to be sigmoidal under fixed PhP concentrations, but substrate inhibition was observed at high PhP concentrations under subsaturating ATP concentrations, suggesting a preferred pathway to ternary complex formation. Negative cooperativity in the kinetic response of MtPPAT to PhP binding was observed under certain conditions and confirmed thermodynamically by isothermal titration calorimetry, suggesting the formation of an asymmetric quaternary structure during sequential ligation of substrates. Asymmetry in binding was also observed in isothermal titration calorimetry experiments with dephosphocoenzyme A and CoA. X-ray structures of MtPPAT in complex with PhP and the nonhydrolyzable ATP analogue adenosine-5-[(α,β)-methyleno]triphosphate were solved to 1.57 A and 2.68 A, respectively. These crystal structures reveal small conformational changes in enzyme structure upon ligand binding, which may play a role in the nonrapid-equilibrium mechanism. We suggest that the proposed kinetic mechanism and asymmetric character in MtPPAT ligand binding may provide a means of reaction and pathway regulation in addition to that of the previously determined CoA feedback.
- Wubben, Thomas J.,Mesecar, Andrew D.
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- An Efficient Chemoenzymatic Synthesis of Coenzyme A and Its Disulfide
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We have developed a chemoenzymatic route to coenzyme A (CoASH) and its disulfide that is amenable to gram-scale synthesis using standard laboratory equipment. By synthesizing the symmetrical disulfide of pantetheine (pantethine), we avoided the need to mask the reactive sulfhydryl and also prevented sulfur oxidation byproducts. No chromatography is required in our synthetic route to pantethine, which facilitates scale-up. Furthermore, we discovered that all three enzymes of the CoASH salvage pathway (pantetheine kinase, phosphopantetheine adenyltransferase, and dephospho-coenzyme A kinase) accept the disulfide of the natural substrates and functionalize both ends of the molecules. This yields CoA disulfide as the product of the enzymatic cascade, a much more stable form of the cofactor. Free CoASH can be prepared by in situ S-S reduction.
- Mouterde, Louis M. M.,Stewart, Jon D.
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p. 954 - 959
(2016/06/13)
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- One-pot chemo-enzymatic synthesis of reporter-modified proteins
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To meet recent advancements in the covalent reporter labeling of proteins, we propose a flexible synthesis for reporter analogs. Here we demonstrate a one-pot chemo-enzymatic synthesis of reporter-labeled proteins that allows the covalent tethering of any amine-terminal fluorescent or affinity label to a carrier protein or fusion construct. This two-reaction sequence consists of activated panthothenate coupling, biosynthetic conversion to the coenzyme A (CoA) analog, and enzymatic carrier protein modification via phosphopantetheinyltransferase (PPTase). We also probe substrate specificity for CoAA, the first enzyme in the pathway. With this approach CoA analogs may be rapidly prepared, thus permitting the regiospecific attachment of reporter moieties from a variety of molecular species. The Royal Society of Chemistry 2006.
- Worthington, Andrew S.,Burkart, Michael D.
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