Theoretical study of the catalytic mechanism of E1 subunit of pyruvate dehydrogenase multienzyme complex from Bacillus stearothermophilus

Quantum chemical studies of the reaction mechanisms of enzymatic CO2 conversion

Enzymatic capture and conversion of carbon dioxide (CO2) into value-added chemicals are of great interest in the field of biocatalysis and have a positive impact on climate change. The quantum chemical methods, recognized as valuable tools for studying reaction mechanisms, have been widely employed in investigating the reaction mechanisms of the enzymes involved in CO2 utilization. In this perspective, we review the mechanistic studies of representative enzymes that are either currently used or have the potential for converting CO2, utilizing the quantum chemical cluster approach and the quantum mechanical/molecular mechanical (QM/MM) method. We begin by summarizing current trends in enzymatic CO2 conversion, followed by a brief description of the computational details of quantum chemical methods. Then, a series of representative examples of the computational modeling of biocatalytic CO2 conversion are presented, including the reduction of CO2 to C1 species (carbon monoxide and formate), and the fixation of CO2 to form aliphatic and aromatic carboxylic acids. The microscopic views of reaction mechanisms obtained from these studies are helpful in guiding the rational design of current enzymes and the discovery of novel enzymes with enhanced performance in converting CO2. Additionally, they provide key information for the de novo design of new-to-nature enzymes. To conclude, we present a perspective on the potential combination of machine learning with quantum description in the study of enzymatic conversion of CO2.

Metabolic adaptations leading to an enhanced lignification in wheat roots under salinity stress

Analysis of salinity tolerance processes in wheat has focused on salt exclusion from shoots while root phenotypes have received limited attention. Here, we consider the varying phenotypic response of four bread wheat varieties that differ in their type and degree of salt tolerance and assess their molecular responses to salinity and changes in root cell wall lignification. These varieties were Westonia introgressed with Nax1 and Nax2 root sodium transporters (HKT1;4-A and HKT1;5-A) that reduce Na+ accumulation in leaves, as well as the 'tissue tolerant' Portuguese landrace Mocho de Espiga Branca that has a mutation in the homologous gene HKT1;5-D and has high Na+ concentration in leaves. These three varieties were compared with the relatively more salt-sensitive cultivar Gladius. Through the use of root histochemical analysis, ion concentrations, as well as differential proteomics and targeted metabolomics, we provide an integrated view of the wheat root response to salinity. We show different metabolic re-arrangements in energy conversion, primary metabolic machinery and phenylpropanoid pathway leading to monolignol production in a genotype and genotype by treatment-dependent manner that alters the extent and localisation of root lignification which correlated with an improved capacity of wheat roots to cope better under salinity stress.

Computational characterization of enzyme-bound thiamin diphosphate reveals a surprisingly stable tricyclic state: implications for catalysis

Thiamin diphosphate (ThDP)-dependent enzymes constitute a large class of enzymes that catalyze a diverse range of reactions. Many are involved in stereospecific carbon–carbon bond formation and, consequently, have found increasing interest and utility as chiral catalysts in various biocatalytic applications. All ThDP-catalyzed reactions require the reaction of the ThDP ylide (the activated state of the cofactor) with the substrate. Given that the cofactor can adopt up to seven states on an enzyme, identifying the factors affecting the stability of the pre-reactant states is important for the overall understanding of the kinetics and mechanism of the individual reactions.

In this paper we use density functional theory calculations to systematically study the different cofactor states in terms of energies and geometries. Benzoylformate decarboxylase (BFDC), which is a well characterized chiral catalyst, serves as the prototypical ThDP-dependent enzyme. A model of the active site was constructed on the basis of available crystal structures, and the cofactor states were characterized in the presence of three different ligands (crystallographic water, benzoylformate as substrate, and (R)-mandelate as inhibitor). Overall, the calculations reveal that the relative stabilities of the cofactor states are greatly affected by the presence and identity of the bound ligands. A surprising finding is that benzoylformate binding, while favoring ylide formation, provided even greater stabilization to a catalytically inactive tricyclic state. Conversely, the inhibitor binding greatly destabilized the ylide formation. Together, these observations have significant implications for the reaction kinetics of the ThDP-dependent enzymes, and, potentially, for the use of unnatural substrates in such reactions.

How phosphorylation influences E1 subunit pyruvate dehydrogenase: A computational study

Pyruvate (PYR) dehydrogenase complex (PDC) is an enzymatic system that plays a crucial role in cellular metabolism as it controls the entry of carbon into the Krebs cycle. From a structural point of view, PDC is formed by three different subunits (E1, E2 and E3) capable of catalyzing the three reaction steps necessary for the full conversion of pyruvate to acetyl-CoA. Recent investigations pointed out the crucial role of this enzyme in the replication and survival of specific cancer cell lines, renewing the interest of the scientific community. Here, we report the results of our molecular dynamics studies on the mechanism by which posttranslational modifications, in particular the phosphorylation of three serine residues (Ser-264-α, Ser-271-α, and Ser-203-α), influence the enzymatic function of the protein. Our results support the hypothesis that the phosphorylation of Ser-264-α and Ser-271-α leads to (1) a perturbation of the catalytic site structure and dynamics and, especially in the case of Ser-264-α, to (2) a reduction in the affinity of E1 for the substrate. Additionally, an analysis of the channels connecting the external environment with the catalytic site indicates that the inhibitory effect should not be due to the occlusion of the access/egress pathways to/from the active site.

A Theoretical Study of the Benzoylformate Decarboxylase Reaction Mechanism

Density functional theory calculations are used to investigate the detailed reaction mechanism of benzoylformate decarboxylase, a thiamin diphosphate (ThDP)-dependent enzyme that catalyzes the nonoxidative decarboxylation of benzoylformate yielding benzaldehyde and carbon dioxide. A large model of the active site is constructed on the basis of the X-ray structure, and it is used to characterize the involved intermediates and transition states and evaluate their energies. There is generally good agreement between the calculations and available experimental data. The roles of the various active site residues are discussed and the results are compared to mutagenesis experiments. Importantly, the calculations identify off-cycle intermediate species of the ThDP cofactor that can have implications on the kinetics of the reaction.

Transcriptome analysis around the onset of strawberry fruit ripening uncovers an important role of oxidative phosphorylation in ripening

Although much progress has been made towards understanding the ripening of non-climacteric fruit using the strawberry as a model plant, the defined molecular mechanisms remain unclear. Here, RNA-sequencing was performed using four cDNA libraries around the onset of ripening, and a total of 31,793 unigenes and 335 pathways were annotated including the top five pathways, which were involved in ribosome, spliceosome, protein processing, plant-pathogen interaction and plant hormone signaling, and the important DEGs related to ripening were annotated to be mainly involved in protein translation and processing, sugar metabolism, energy metabolism, phytohormones, antioxidation, pigment and softening, especially finding a decreased trend of oxidative phosphorylation during red-coloring. VIGS-mediated downregulation of the pyruvate dehydrogenase gene PDHE1α, a key gene for glycolysis-derived oxidative phosphorylation, could inhibit respiration and ATP biosynthesis, whilst promote the accumulation of sugar, ABA, ETH, and PA, ultimately accelerating the ripening. In conclusion, our results demonstrate that a set of metabolism transition occurred during green-to-white-to-red stages that are coupled with more-to-less DEGs, and the oxidative phosphorylation plays an important role in the regulation of ripening. On the basis of our results, we discuss an oxidative phosphorylation-based model underlying strawberry fruit ripening.

Subsite-specific contributions of different aromatic residues in the active site architecture of glycoside hydrolase family 12

The active site architecture of glycoside hydrolase (GH) is a contiguous subregion of the enzyme constituted by residues clustered in the three-dimensional space, recognizing the monomeric unit of ligand through hydrogen bonds and hydrophobic interactions. Mutations of the key residues in the active site architecture of the GH12 family exerted different impacts on catalytic efficiency. Binding affinities between the aromatic amino acids and carbohydrate rings were quantitatively determined by isothermal titration calorimetry (ITC) and the quantum mechanical (QM) method, showing that the binding capacity order of Tyr>Trp>His (and Phe) was determined by their side-chain properties. The results also revealed that the binding constant of a certain residue remained unchanged when altering its location, while the catalytic efficiency changed dramatically. Increased binding affinity at a relatively distant subsite, such as the mutant of W7Y at the -4 subsite, resulted in a marked increase in the intermediate product of cellotetraose and enhanced the reactivity of endoglucanase by 144%; while tighter binding near the catalytic center, i.e. W22Y at the -2 subsite, enabled the enzyme to bind and hydrolyze smaller oligosaccharides. Clarification of the specific roles of the aromatics at different subsites may pave the way for a more rational design of GHs.

Computational Evidence for the Catalytic Mechanism of Tyrosylprotein Sulfotransferases: A Density Functional Theory Investigation

In this paper we have examined the mechanism of tyrosine O-sulfonation catalyzed by human TPST-2. Our computations, in agreement with Teramoto's hypothesis, indicate a concerted SN2-like reaction (with an activation barrier of 18.2 kcal mol(-1)) where the tyrosine oxygen is deprotonated by Glu(99) (base catalyst) and simultaneously attacks as a nucleophile the sulfuryl group. For the first time, using a quantum mechanics protocol of alanine scanning, we identified unequivocally the role of the amino acids involved in the catalysis. Arg(78) acts as a shuttle that "assists" the sulfuryl group moving from the 3'-phosphoadenosine-5'-phosphosulfate molecule to threonine and stabilizes the transition state (TS) by electrostatic interactions. The residue Lys(158) keeps close the residues participating in the overall H-bond network, while Ser(285), Thr(81), and Thr(82) stabilize the TS via strong hydrogen interactions and contribute to lower the activation barrier.