Showcasing research from Professor Caballero, Cabrera and As featured in: Tuñón laboratories, Universities of Chile and Talca (Chile) and Valencia (Spain). Studying the phosphoryl transfer mechanism of the E. coli phosphofructokinase-2: from X-ray structure to quantum mechanics/molecular mechanics simulations Phosphoryl transfer reactions are crucial for metabolic pathways and cellular signaling transduction and, in particular, the reaction catalyzed by the enzyme Pfk-2 is believed to have an important role in glycolysis regulation. In this work we present a combined experimental and theoretical analysis on this enzyme, involving X-ray crystallography molecular dynamics simulations and QM/ MM calculations, in order to elucidate the reaction mechanism See Julio Caballero, Iñaki Tuñón, for the phosphoryl transfer in a phosphofructokinase. Ricardo Cabrera et al., Chem. Sci., 2019, 10, 2882. rsc.li/chemical-science Registered charity number: 207890 Chemical Science View Article Online EDGE ARTICLE View Journal | View Issue Studying the phosphoryl transfer mechanism of the E. coli phosphofructokinase-2: from X-ray structure Cite this: Chem. Sci.,2019,10, 2882 All publication charges for this article to quantum mechanics/molecular mechanics have been paid for by the Royal Society † of Chemistry simulations a b c d Juliana Murillo-Lopez,´ ‡ Kirill Zinovjev,‡ Humberto Pereira, Andres Caniuguir, Richard Garratt,c Jorge Babul,d Rodrigo Recabarren,a Jans Alzate-Morales,a a b d Julio Caballero, * Inaki˜ Tun˜on´ * and Ricardo Cabrera* Phosphofructokinases (Pfks) catalyze the ATP-dependent phosphorylation of fructose-6-phosphate (F6P) and they are regulated in a wide variety of organisms. Although numerous aspects of the kinetics and regulation have been characterized for Pfks, the knowledge about the mechanism of the phosphoryl transfer reaction and the transition state lags behind. In this work, we describe the X-ray crystal structure of the homodimeric Pfk-2 from E. coli, which contains products in one site and reactants in the other, as Creative Commons Attribution-NonCommercial 3.0 Unported Licence. well as an additional ATP molecule in the inhibitory allosteric site adjacent to the reactants. This complex was previously predicted when studying the kinetic mechanism of ATP inhibition. After removing the allosteric ATP, molecular dynamic (MD) simulations revealed conformational changes related to domain packing, as well as stable interactions of Lys27 and Asp256 with donor (ATP) and acceptor (fructose-6-) groups, and of Asp166 with Mg2+. The phosphoryl transfer reaction mechanism catalyzed by Pfk-2 was investigated through Quantum Mechanics/Molecular Mechanics (QM/MM) simulations using a combination of the string method and a path-collective variable for the exploration of its free energy Received 7th January 2019 surface. The calculated activation free energies showed that a dissociative mechanism, occurring with Accepted 24th January 2019 This article is licensed under a a metaphosphate intermediate formation followed by a proton transfer to Asp256, is more favorable DOI: 10.1039/c9sc00094a than an associative one. The structural analysis reveals the role of Asp256 acting as a catalytic base and rsc.li/chemical-science Lys27 stabilizing the transition state of the dissociative mechanism. Open Access Article. Published on 28 January 2019. Downloaded 10/7/2021 1:24:56 PM. 1. Introduction (fructose-6-P kinase, P), which is believed to have an impor- tant role in glycolysis regulation.12 In Escherichia coli, this Phosphoryl transfer reactions are crucial for metabolic path- reaction is performed by two non-homologous isoenzymes, P- ways and cellular signaling transduction.1–4 These reactions are 1 and P-2.12 P-2, the minor isoenzyme, is one of the most catalyzed by kinases that transfer the terminal phosphate group extensively characterized member of the ribokinase-like super- from the phosphoryl donor (most commonly ATP) to nucleo- family,13,14 which includes ribokinases, fructokinases, fructose- philic groups on the acceptor molecule, which could be small 1-P kinases, tagatose-6-P kinases and nucleoside kinases, molecules such as sugars and lipids, or the side chains of among others.13,15 In this superfamily the phosphoryl transfer particular residues in proteins.5–11 The ATP-dependent phos- process has been studied by in vacuo QM calculations of phorylation of fructose-6-phosphate (F6P) to yield fructose-1,6- a reduced active site of thiazole kinase, ThiK, a distant homo- bisphosphate (FBP) is catalyzed by phosphofructokinase logue of P-2.16,17 Although a QM/MM calculation was not performed in that contribution, their ndings help to identify residues important for transition state stabilization, albeit aCentro de Bioinformatica´ y Simulacion´ Molecular (CBSM), Facultad de Ingenier´ıa, noting that a more realistic catalytic environment should be Universidad de Talca, 1 Poniente 1141, Talca, Chile. E-mail: [email protected] considered. In the light of this prior information, however, the b ı ı Departament de Qu´mica F´sica, Universitat de Val`encia, 46100 Burjassot, Spain. E-mail: [email protected] phosphoryl transfer for P s has not been studied so far. cInstituto de F´ısica de Sao˜ Carlos, Universidade de Sao˜ Paulo, Sao˜ Paulo, Brazil X-ray structures of P -2 with the F6P substrate (PDB ID: 2À dDepartamento de Biolog´ıa, Facultad de Ciencias, Universidad de Chile, Santiago, 3N1C) and with two MgATP (PDB ID: 3CQD) have been Chile. E-mail: [email protected] previously reported. There are few kinase structures in the † Electronic supplementary information (ESI) available. See DOI: Protein Data Bank (PDB) that are bound to both reactants and 10.1039/c9sc00094a products, namely the xylulose kinase from Lactobacillus ‡ These authors contributed equally. 2882 | Chem. Sci.,2019,10,2882–2892 This journal is © The Royal Society of Chemistry 2019 View Article Online Edge Article Chemical Science acidophilus (PDB ID: 3LL3), phosphoglycerate kinase from the sugar phosphate substrate would be transferred to one of Homo sapiens (PDB ID: 2X15) and adenylate kinase from Plas- the non-bridging oxygen atoms of the phosphate group (see modium falciparum (PDB ID: 3TLX), which has not been asso- Fig. S1 in the ESI,† lower mechanism), decreasing its charge and ciated to any publication, and, noteworthy, the P-1 from E. coli favoring the approach to the nucleophile. On the other hand, in 18 with its reaction products. In this work, for the rst time, we the dissociative or elimination–addition (DN +AN) mechanism, report the structure of a member of the ribokinase family (P-2) the reaction proceeds via an expansive transition state (TS) with solved with both reactants and products in the same crystal metaphosphate character, where bond cleavage of the leaving (PDB ID: 3UQD). Thus, this crystallographic structure could group occurs prior to bond formation with the nucleophile. If serve as a model to study the chemical reaction catalyzed by the the phosphoryl transfer of P-2 followed this mechanism, the enzyme, as it provides information not only about the position carboxylate group in a side chain would act as the base of each ligand at the beginning and the end of the phosphory- responsible for substrate deprotonation. In this case, the formal lation reaction but also about the residues performing key negative charges born by both the phosphate group and the interactions that could be relevant for the catalytic activity of the nucleophile would then favor a dissociative mechanism. This enzyme. same carboxylate group would then act as an acid to protonate The ribokinase superfamily has been studied in terms of the transferred phosphoryl group and thus regenerate the evolution, showing that the overall fold and reaction machinery enzyme to its original state. This last step has been studied at are strongly conserved over a wide range of species and the quantum mechanics/molecular mechanics (QM/MM) level substrate specicities.19 In this family, the general chemical in protein kinases, demonstrating its feasibility.38 reaction consists of the ATP-dependent phosphorylation of In this work, we describe the crystallographic structure of a hydroxymethyl group in the substrates.13 Although the P-2 with products in one active site and reactants in the other, À sequence similarities of these proteins are in the range of 18– plus an additional MgATP2 positioned in the allosteric site 22%,20 the alignment of different protein–ligand complexes adjacent to reactants. With this structure we performed an in- Creative Commons Attribution-NonCommercial 3.0 Unported Licence. reveals conserved regions that are important for catalysis and depth theoretical study of the phosphorylation reaction mech- protein stabilization.14,21–24 These conserved regions have been anism, using highly parallelized computational techniques. The targets of multiple studies, with P-2 being the most studied comparison of the interactions observed in the crystal, and phosphosugar kinase member at the biochemical and struc- during MD simulations of the active sites containing reactants tural level.12,14,24–34 Noteworthy, the GXGD14,35 motif contains and products, allows the identication of a conformational a highly conserved aspartate residue, for which the D256N change in the chain bearing the products that is essential for mutation in P-2 produced a striking 15 000-fold decrease in the reaction to take place. Furthermore, Lys27 adopts a better the catalytic constant with no variation in the KM values for F6P conformation for the reaction and Asp166 joins the coordina- À or MgATP2 . This result indicates that Asp256 participates tion sphere of Mg2+, replacing a water molecule. QM/MM This article is licensed under a specically in catalysis but not in substrate binding in P-2.14 calculations were performed considering the effect of the This residue has also been proposed to have a catalytic role in D- protein environment and its exibility.39 We determined that tagatose-6-P kinase (LacC), which is closely related to P-2. In P-2 follows a dissociative phosphorylation mechanism during 36 Open Access Article.