Structural analysis of a 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase with an N-terminal chorismate mutase-like regulatory domain

A secreted form of chorismate mutase (Rv1885c) in Mycobacterium bovis BCG contributes to pathogenesis by inhibiting mitochondria-mediated apoptotic cell death of macrophages

BACKGROUND

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB), and its pathogenicity is associated with its ability to evade the host defense system. The secretory form of the chorismate mutase of M. tuberculosis (TBCM, encoded by Rv1885c) is assumed to play a key role in the pathogenesis of TB; however, the mechanism remains unknown.

METHODS

A tbcm deletion mutant (B∆tbcm) was generated by targeted gene knockout in BCG to investigate the pathogenic role of TBCM in mice or macrophages. We compared the pathogenesis of B∆tbcm and wild-type BCG in vivo by measuring the bacterial clearance rate and the degree of apoptosis. Promotion of the intrinsic apoptotic pathway was evaluated in infected bone marrow-derived macrophages (BMDMs) by measuring apoptotic cell death, loss of mitochondrial membrane potential and translocation of pore-forming proteins. Immunocytochemistry, western blotting and real-time PCR were also performed to assess the related protein expression levels after infection. Furthermore, these findings were validated by complementation of tbcm in BCG.

RESULTS

Deletion of the tbcm gene in BCG leads to reduced pathogenesis in a mouse model, compared to wild type BCG, by promoting apoptotic cell death and bacterial clearance. Based on these findings, we found that intrinsic apoptosis and mitochondrial impairment were promoted in B∆tbcm-infected BMDMs. B∆tbcm down-regulates the expression of Bcl-2, which leads to mitochondrial outer membrane permeabilization (MOMP), culminating in cytochrome c release from mitochondria. Consistent with this, transcriptome profiling also indicated that B∆tbcm infection is more closely related to altered mitochondrial-related gene expression than wild-type BCG infection, suggesting an inhibitory role of TBCM in mitochondrial dysfunction. Moreover, genetic complementation of B∆tbcm (C∆tbcm) restored its capacity to inhibit mitochondria-mediated apoptotic cell death.

CONCLUSIONS

Our findings demonstrate the contribution of TBCM to bacterial survival, inhibiting intrinsic apoptotic cell death of macrophages as a virulence factor of M. tuberculosis complex (MTBC) strains, which could be a potential target for the development of TB therapy.

Influence of Cysteine 440 on the Active Site Properties of 3-Deoxy-d-Arabino-Heptulosonate 7-Phosphate Synthase in Mycobacterium tuberculosis (MtDAHPS)

The shikimate pathway, which produces aromatic amino acids and key intermediates, is critical to the viability of the tuberculosis-causing pathogen Mycobacterium tuberculosis. The enzyme 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAHPS) catalyzes the first committed step of this pathway and possesses regulatory functions. Its active site contains two cysteinyls: one (Cys₈₇) bound to a metal ion, while the other (Cys₄₄₀) is in proximity to the first but is located on a connecting loop. This arrangement seemingly appeared as a disulfide linkage. However, Cys₄₄₀ is not metal binding, and its positioning indicates that it could collapse the disulfide linkage. Hence, its potential role may be more than simply structural support of the active site fold. Using a multiscale computational approach, molecular dynamics (MD) simulations, and DFT-based calculations, the influence of Cys₄₄₀ on the active site properties has been investigated. MD simulations reveal an unusually long disulfide bond, more than 3.0 Å, whereas DFT calculations identified two stable active site conformers in the triplet and quintet spin states. Analysis of group spin density distribution identified antiferromagnetic coupling in each conformer, which suggests their relatively low potential energy and stable conformations. The conformer in the triplet spin state could favor enzyme reactivity due to its low HOMO-LUMO energy gap. In addition, reduction of the Cys₄₄₀ thiolate group results in collapse of the active site metal-ligand configuration with large exothermicity. Hence, Cys₄₄₀ could activate and inactivate the enzyme. For the first time, the study revealed the role of Cys₄₄₀ as being vital for the catalytic activity of the enzyme rather than solely for the structural stabilization of its active site. Thus, the findings may lead to a novel basis for antituberculosis drug design and development that would disrupt the contributions of the Cys₄₄₀.

Role of Half-of-Sites Reactivity and Inter-Subunit Communications in DAHP Synthase Catalysis and Regulation

α-Carboxyketose synthases, including 3-deoxy-d-arabinoheptulosonate 7-phosphate synthase (DAHPS), are long-standing targets for inhibition. They are challenging targets to create tight-binding inhibitors against, and inhibitors often display half-of-sites binding and partial inhibition. Half-of-sites inhibition demonstrates the existence of inter-subunit communication in DAHPS. We used X-ray crystallography and spatially resolved hydrogen-deuterium exchange (HDX) to reveal the structural and dynamic bases for inter-subunit communication in Escherichia coli DAHPS(Phe), the isozyme that is feedback-inhibited by phenylalanine. Crystal structures of this homotetrameric (dimer-of-dimers) enzyme are invariant over 91% of its sequence. Three variable loops make up 8% of the sequence and are all involved in inter-subunit contacts across the tight-dimer interface. The structures have pseudo-twofold symmetry indicative of inter-subunit communication across the loose-dimer interface, with the diagonal subunits B and C always having the same conformation as each other, while subunits A and D are variable. Spatially resolved HDX reveals contrasting responses to ligand binding, which, in turn, affect binding of the second substrate, erythrose-4-phosphate (E4P). The N-terminal peptide, M1-E12, and the active site loop that binds E4P, F95-K105, are key parts of the communication network. Inter-subunit communication appears to have a catalytic role in all α-carboxyketose synthase families and a regulatory role in some members.

Characterization of two 3-deoxy-d-Arabino-Heptulosonate 7-phosphate synthases from Bacillusmethanolicus

3-Deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthase catalyzes the condensation of phosphoenolpyruvate (PEP) with d-erythrose 4-phosphate (E4P) and plays an important role in regulating carbon flux toward aromatic amino acid biosynthesis in bacteria and plants. Sequence analysis of the DAHP synthases AroG1 and AroG2 from Bacillus methanolicus MGA3 suggested this thermophilic, methylotrophic bacterium possesses two type Iβ DAHP synthases. This study describes production of AroG1 and AroG2 in Escherichia coli as hexa-histidine fused proteins, which were purified by affinity chromatography. Treatment with TEV protease afforded native proteins for characterization and kinetic analysis. AroG1 and AroG2 are, respectively, 30.1 kDa and 40.0 kDa proteins. Both enzymes have maximal activity over a pH range of 6.3-7.2. The apparent kinetic parameters at 50 °C and pH 7.2 for AroG1 are K_m^PEP 1100 ± 100 μM, K_m^E4P 530 ± 100 μM, and k_cat 10.3 ± 1.2 s^-1. The kinetic parameters for AroG2 are K_m^PEP 90 ± 20 μM, K_m^E4P 130 ± 40 μM, and k_cat 2.0 ± 0.2 s^-1. At 50 °C AroG2 retains 50% of its activity after 96 min whereas AroG1 retains less than 5% of its activity after 10 min. AroG2, which contains an N-terminal regulatory domain, is inhibited by chorismate and prephenate but not l-phenylalanine, l-tyrosine, or l-tryptophan. AroG1 is not inhibited by any of the molecules examined. Understanding DAHP synthase regulation in B. methanolicus is a first step toward generating biocatalysts that exploit the target-rich aromatic amino acid biosynthetic pathway for synthesis of chemicals from methanol.

Reciprocal allostery arising from a bienzyme assembly controls aromatic amino acid biosynthesis in Prevotella nigrescens

Modular protein assembly has been widely reported as a mechanism for constructing allosteric machinery. Recently, a distinctive allosteric system has been identified in a bienzyme assembly comprising a 3-deoxy-d-arabino heptulosonate-7-phosphate synthase (DAH7PS) and chorismate mutase (CM). These enzymes catalyze the first and branch point reactions of aromatic amino acid biosynthesis in the bacterium Prevotella nigrescens (PniDAH7PS), respectively. The interactions between these two distinct catalytic domains support functional interreliance within this bifunctional enzyme. The binding of prephenate, the product of CM-catalyzed reaction, to the CM domain is associated with a striking rearrangement of overall protein conformation that alters the interdomain interactions and allosterically inhibits the DAH7PS activity. Here, we have further investigated the complex allosteric communication demonstrated by this bifunctional enzyme. We observed allosteric activation of CM activity in the presence of all DAH7PS substrates. Using small-angle X-ray scattering (SAXS) experiments, we show that changes in overall protein conformations and dynamics are associated with the presence of different DAH7PS substrates and the allosteric inhibitor prephenate. Furthermore, we have identified an extended interhelix loop located in CM domain, loop_C320-F333, as a crucial segment for the interdomain structural and catalytic communications. Our results suggest that the dual-function enzyme PniDAH7PS contains a reciprocal allosteric system between the two enzymatic moieties as a result of this bidirectional interdomain communication. This arrangement allows for a complex feedback and feedforward system for control of pathway flux by connecting the initiation and branch point of aromatic amino acid biosynthesis.

Computational investigations of allostery in aromatic amino acid biosynthetic enzymes

Allostery, in which binding of ligands to remote sites causes a functional change in the active sites, is a fascinating phenomenon observed in enzymes. Allostery can occur either with or without significant conformational changes in the enzymes, and the molecular basis of its mechanism can be difficult to decipher using only experimental techniques. Computational tools for analyzing enzyme sequences, structures, and dynamics can provide insights into the allosteric mechanism at the atomic level. Combining computational and experimental methods offers a powerful strategy for the study of enzyme allostery. The aromatic amino acid biosynthesis pathway is essential in microorganisms and plants. Multiple enzymes involved in this pathway are sensitive to feedback regulation by pathway end products and are known to use allostery to control their activities. To date, four enzymes in the aromatic amino acid biosynthesis pathway have been computationally investigated for their allosteric mechanisms, including 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase, anthranilate synthase, chorismate mutase, and tryptophan synthase. Here we review the computational studies and findings on the allosteric mechanisms of these four enzymes. Results from these studies demonstrate the capability of computational tools and encourage future computational investigations of allostery in other enzymes of this pathway.

Biotechnological Advances in Resveratrol Production and its Chemical Diversity

The very well-known bioactive natural product, resveratrol (3,5,4'-trihydroxystilbene), is a highly studied secondary metabolite produced by several plants, particularly grapes, passion fruit, white tea, and berries. It is in high demand not only because of its wide range of biological activities against various kinds of cardiovascular and nerve-related diseases, but also as important ingredients in pharmaceuticals and nutritional supplements. Due to its very low content in plants, multi-step isolation and purification processes, and environmental and chemical hazards issues, resveratrol extraction from plants is difficult, time consuming, impracticable, and unsustainable. Therefore, microbial hosts, such as Escherichia coli, Saccharomyces cerevisiae, and Corynebacterium glutamicum, are commonly used as an alternative production source by improvising resveratrol biosynthetic genes in them. The biosynthesis genes are rewired applying combinatorial biosynthetic systems, including metabolic engineering and synthetic biology, while optimizing the various production processes. The native biosynthesis of resveratrol is not present in microbes, which are easy to manipulate genetically, so the use of microbial hosts is increasing these days. This review will mainly focus on the recent biotechnological advances for the production of resveratrol, including the various strategies used to produce its chemically diverse derivatives.

Isolation and biochemical characterization of a metagenome-derived 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase gene from subtropical marine mangrove wetland sediments

3-Deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS) is a key rate-limiting enzyme in aromatic amino acid anabolism. A new I_β-type DAHPS gene (aro1A) was identified in a metagenomic library from subtropical marine mangrove sediment. The gene encoded a polypeptide composed of 272 amino acids and had a maximum similarity of 52.4% to a known DAHPS at the amino acid level. Multiple sequence alignment, homologous modeling, and molecular docking showed that Aro1A had the typical (β/α)₈ barrel-shaped catalytic structural domain of DAHPS. The motifs and amino acid residues involved in the combination of substrates and metal ligand were highly conservative with the known DAHPS. The putative DAHPS gene was subcloned into a pET-30a(+) vector and was overexpressed in Escherichia coli Rosetta (DE3) cells. The recombinant protein was purified to homogeneity. The maximum activity for the recombinant Aro1A protein occurred at pH 8.0 and 40 °C. Ba²⁺ and Ca²⁺ stimulated the activity of Aro1A protein. The enzyme showed high affinity and catalytic efficiency (K _m ^PEP  = 19.58 μM, V _max ^PEP   = 29.02 μM min^-1, and k _cat ^PEP /K _m ^PEP  = 0.88 s^-1 μM^-1) under optimal reaction conditions. The enzymatic property of Aro1A indicates its potential in aromatic amino acid industrial production.

Domain cross-talk within a bifunctional enzyme provides catalytic and allosteric functionality in the biosynthesis of aromatic amino acids

Because of their special organization, multifunctional enzymes play crucial roles in improving the performance of metabolic pathways. For example, the bacterium Prevotella nigrescens contains a distinctive bifunctional protein comprising a 3-deoxy-d-arabino heptulosonate-7-phosphate synthase (DAH7PS), catalyzing the first reaction of the biosynthetic pathway of aromatic amino acids, and a chorismate mutase (CM), functioning at a branch of this pathway leading to the synthesis of tyrosine and phenylalanine. In this study, we characterized this P. nigrescens enzyme and found that its two catalytic activities exhibit substantial hetero-interdependence and that the separation of its two distinct catalytic domains results in a dramatic loss of both DAH7PS and CM activities. The protein displayed a unique dimeric assembly, with dimerization solely via the CM domain. Small angle X-ray scattering (SAXS)-based structural analysis of this protein indicated a DAH7PS-CM hetero-interaction between the DAH7PS and CM domains, unlike the homo-association between DAH7PS domains normally observed for other DAH7PS proteins. This hetero-interaction provides a structural basis for the functional interdependence between the two domains observed here. Moreover, we observed that DAH7PS is allosterically inhibited by prephenate, the product of the CM-catalyzed reaction. This allostery was accompanied by a striking conformational change as observed by SAXS, implying that altering the hetero-domain interaction underpins the allosteric inhibition. We conclude that for this C-terminal CM-linked DAH7PS, catalytic function and allosteric regulation appear to be delivered by a common mechanism, revealing a distinct and efficient evolutionary strategy to utilize the functional advantages of a bifunctional enzyme.

Structural and functional characterisation of the entry point to pyocyanin biosynthesis in Pseudomonas aeruginosa defines a new 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase subclass

In Pseudomonas aeruginosa (Pae), the shikimate pathway end product, chorismate, serves as the last common precursor for the biosynthesis of both primary aromatic metabolites, including phenylalanine, tyrosine and tryptophan, and secondary aromatic metabolites, including phenazine-1-carboxylic acid (PCA) and pyocyanin (PYO). The enzyme 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAH7PS) catalyses the first committed step of the shikimate pathway, en route to chorismate. P. aeruginosa expresses multiple, distinct DAH7PSs that are associated with either primary or secondary aromatic compound biosynthesis. Here we report the structure of a type II DAH7PS, encoded by phzC as part of the duplicated phenazine biosynthetic cluster, from P. aeruginosa (PAO1) revealing for the first time the structure of a type II DAH7PS involved in secondary metabolism. The omission of the structural elements α_2a and α_2b, relative to other characterised type II DAH7PSs, leads to the formation of an alternative, dimeric, solution-state structure for this type II DAH7PS with an oligomeric interface that has not previously been characterised and that does not facilitate the formation of aromatic amino acid allosteric binding sites. The sequence similarity and, in particular, the common N-terminal extension suggest a common origin for the type II DAH7PSs from P. aeruginosa. The results described in the present study support an expanded classification of the type II DAH7PSs as type II_A and type II_B based on sequence characteristics, structure and function of the resultant proteins, and on defined physiological roles within primary or secondary metabolism.

Heterologous production of resveratrol in bacterial hosts: current status and perspectives

The polyphenol resveratrol (3,5,4'-trihydroxystilbene) is a well-known plant secondary metabolite, commonly used as a medical ingredient and a nutritional supplement. Due to its health-promoting properties, the demand for resveratrol is expected to continue growing. This stilbene can be found in different plants, including grapes, berries (blackberries, blueberries and raspberries), peanuts and their derived food products, such as wine and juice. The commercially available resveratrol is usually extracted from plants, however this procedure has several drawbacks such as low concentration of the product of interest, seasonal variation, risk of plant diseases and product stability. Alternative production processes are being developed to enable the biotechnological production of resveratrol by genetically engineering several microbial hosts, such as Escherichia coli, Corynebacterium glutamicum, Lactococcus lactis, among others. However, these bacterial species are not able to naturally synthetize resveratrol and therefore genetic modifications have been performed. The application of emerging metabolic engineering offers new possibilities for strain and process optimization. This mini-review will discuss the recent progress on resveratrol biosynthesis in engineered bacteria, with a special focus on the metabolic engineering modifications, as well as the optimization of the production process. These strategies offer new tools to overcome the limitations and challenges for microbial production of resveratrol in industry.

Exploring modular allostery via interchangeable regulatory domains

Most proteins comprise two or more domains from a limited suite of protein families. These domains are often rearranged in various combinations through gene fusion events to evolve new protein functions, including the acquisition of protein allostery through the incorporation of regulatory domains. The enzyme 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAH7PS) is the first enzyme of aromatic amino acid biosynthesis and displays a diverse range of allosteric mechanisms. DAH7PSs adopt a common architecture with a shared (β/α)₈ catalytic domain which can be attached to an ACT-like or a chorismate mutase regulatory domain that operates via distinct mechanisms. These respective domains confer allosteric regulation by controlling DAH7PS function in response to ligand Tyr or prephenate. Starting with contemporary DAH7PS proteins, two protein chimeras were created, with interchanged regulatory domains. Both engineered proteins were catalytically active and delivered new functional allostery with switched ligand specificity and allosteric mechanisms delivered by their nonhomologous regulatory domains. This interchangeability of protein domains represents an efficient method not only to engineer allostery in multidomain proteins but to create a new bifunctional enzyme.

Structure of Chorismate Mutase-like Domain of DAHPS from Bacillus subtilis Complexed with Novel Inhibitor Reveals Conformational Plasticity of Active Site

3-deoxy-D-arabino-heptulosonate-7-phosphate-synthase (DAHPS) is the first enzyme of the shikimate pathway and is responsible for the synthesis of aromatic amino acids in microorganisms. This pathway is an attractive target for antimicrobial drugs. In Bacillus subtilis, the N-terminal domain of the bifunctional DAHPS enzyme belongs to an AroQ class of chorismate mutase and is functionally homologous to the downstream AroH class chorismate mutase. This is the first structure of chorismate mutase, AroQ (BsCM_2) enzyme from Bacillus subtilis in complex with citrate and chlorogenic acid at 1.9 Å and 1.8 Å resolution, respectively. This work provides the structural basis of ligand binding into the active site of AroQ class of chorismate mutase, while accompanied by the conformational flexibility of active site loop. Molecular dynamics results showed that helix H2′ undergoes uncoiling at the first turn and increases the mobility of loop L1′. The side chains of Arg45, Phe46, Arg52 and Lys76 undergo conformational changes, which may play an important role in DAHPS regulation by the formation of the domain-domain interface. Additionally, binding studies showed that the chlorogenic acid binds to BsCM_2 with a higher affinity than chorismate. These biochemical and structural findings could lead to the development of novel antimicrobial drugs.

Interdomain Conformational Changes Provide Allosteric Regulation en Route to Chorismate

Multifunctional proteins play a variety of roles in metabolism. Here, we examine the catalytic function of the combined 3-deoxy-d-arabino heptulosonate-7-phosphate synthase (DAH7PS) and chorismate mutase (CM) from Geobacillus sp. DAH7PS operates at the start of the biosynthetic pathway for aromatic metabolites, whereas CM operates in a dedicated branch of the pathway for the biosynthesis of amino acids tyrosine and phenylalanine. In line with sequence predictions, the two catalytic functions are located in distinct domains, and these two activities can be separated and retain functionality. For the full-length protein, prephenate, the product of the CM reaction, acts as an allosteric inhibitor for the DAH7PS. The crystal structure of the full-length protein with prephenate bound and the accompanying small angle x-ray scattering data reveal the molecular mechanism of the allostery. Prephenate binding results in the tighter association between the dimeric CM domains and the tetrameric DAH7PS, occluding the active site and therefore disrupting DAH7PS function. Acquisition of a physical gating mechanism to control catalytic function through gene fusion appears to be a general mechanism for providing allostery for this enzyme.

Allosteric inhibitor specificity of Thermotoga maritima 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase

3-Deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAH7PS) catalyses the first step of the shikimate pathway for the biosynthesis of aromatic amino acids. Allosteric regulation of Thermotoga maritima DAH7PS is mediated by L-Tyr binding to a discrete ACT regulatory domain appended to a core catalytic (β/α)8 barrel. Variants of T. maritima DAH7PS (TmaDAH7PS) were created to probe the role of key residues in inhibitor selection. Substitution Ser31Gly severely reduced inhibition by L-Tyr. In contrast both L-Tyr and L-Phe inhibited the TmaHis29Ala variant, while the variant where Ser31 and His29 were interchanged (His29Ser/Ser31His), was inhibited to a greater extent by L-Phe than L-Tyr. These studies highlight the role and importance of His29 and Ser31 for determining both inhibitory ligand selectivity and the potency of allosteric response by TmaDAH7PS.

Neisseria meningitidis expresses a single 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase that is inhibited primarily by phenylalanine

Neisseria meningitidis is the causative agent of meningitis and meningococcal septicemia is a major cause of disease worldwide, resulting in brain damage and hearing loss, and can be fatal in a large proportion of cases. The enzyme 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAH7PS) catalyzes the first reaction in the shikimate pathway leading to the biosynthesis of aromatic metabolites including the aromatic acids l-Trp, l-Phe, and l-Tyr. This pathway is absent in humans, meaning that enzymes of the pathway are considered as potential candidates for therapeutic intervention. As the entry point, feedback inhibition of DAH7PS by pathway end products is a key mechanism for the control of pathway flux. The structure of the single DAH7PS expressed by N. meningitidis was determined at 2.0 Å resolution. In contrast to the other DAH7PS enzymes, which are inhibited only by a single aromatic amino acid, the N. meningitidis DAH7PS was inhibited by all three aromatic amino acids, showing greatest sensitivity to l-Phe. An N. meningitidis enzyme variant, in which a single Ser residue at the bottom of the inhibitor-binding cavity was substituted to Gly, altered inhibitor specificity from l-Phe to l-Tyr. Comparison of the crystal structures of both unbound and Tyr-bound forms and the small angle X-ray scattering profiles reveal that N. meningtidis DAH7PS undergoes no significant conformational change on inhibitor binding. These observations are consistent with an allosteric response arising from changes in protein motion rather than conformation, and suggest ligands that modulate protein dynamics may be effective inhibitors of this enzyme.

The diversity of allosteric controls at the gateway to aromatic amino acid biosynthesis

Present within bacteria, plants, and some lower eukaryotes 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAHPS) catalyzes the first committed step in the synthesis of a number of metabolites, including the three aromatic amino acids phenylalanine, tyrosine, and tryptophan. Catalyzing the first reaction in an important biosynthetic pathway, DAHPS is situated at a critical regulatory checkpoint-at which pathway input can be efficiently modulated to respond to changes in the concentration of pathway outputs. Based on a phylogenetic classification scheme, DAHPSs have been divided into three major subtypes (Iα, Iβ, and II). These subtypes are subjected to an unusually diverse pattern of allosteric regulation, which can be used to further subdivide the enzymes. Crystal structures of most of the regulatory subclasses have been determined. When viewed collectively, these structures illustrate how distinct mechanisms of allostery are applied to a common catalytic scaffold. Here, we review structural revelations regarding DAHPS regulation and make the case that the functional difference between the three major DAHPS subtypes relates to basic distinctions in quaternary structure and mechanism of allostery.

Engineering allosteric control to an unregulated enzyme by transfer of a regulatory domain

Allosteric regulation of protein function is a critical component of metabolic control. Its importance is underpinned by the diversity of mechanisms and its presence in all three domains of life. The first enzyme of the aromatic amino acid biosynthesis, 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase, shows remarkable variation in allosteric response and machinery, and both contemporary regulated and unregulated orthologs have been described. To examine the molecular events by which allostery can evolve, we have generated a chimeric protein by joining the catalytic domain of an unregulated 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase with the regulatory domain of a regulated enzyme. We demonstrate that this simple gene fusion event on its own is sufficient to confer functional allostery to the unregulated enzyme. The fusion protein shares structural similarities with its regulated parent protein and undergoes an analogous major conformational change in response to the binding of allosteric effector tyrosine to the regulatory domain. These findings help delineate a remarkably facile mechanism for the evolution of modular allostery by domain recruitment.