N1 Atom Research Articles

Hydride Abstraction as the Rate-Limiting Step of the Irreversible Inhibition of Monoamine Oxidase B by Rasagiline and Selegiline: A Computational Empirical Valence Bond Study.

Monoamine oxidases (MAOs) catalyze the degradation of a very broad range of biogenic and dietary amines including many neurotransmitters in the brain, whose imbalance is extensively linked with the biochemical pathology of various neurological disorders, and are, accordingly, used as primary pharmacological targets to treat these debilitating cognitive diseases. Still, despite this practical significance, the precise molecular mechanism underlying the irreversible MAO inhibition with clinically used propargylamine inhibitors rasagiline and selegiline is still not unambiguously determined, which hinders the rational design of improved inhibitors devoid of side effects current drugs are experiencing. To address this challenge, we present empirical valence bond QM/MM simulations of the rate-limiting step of the MAO inhibition involving the hydride anion transfer from the inhibitor α-carbon onto the N5 atom of the flavin adenin dinucleotide (FAD) cofactor. The proposed mechanism is strongly supported by the obtained free energy profiles, which confirm a higher reactivity of selegiline over rasagiline, while the calculated difference in the activation Gibbs energies of ΔΔG‡ = 3.1 kcal mol−1 is found to be in very good agreement with that from the measured literature kinact values that predict a 1.7 kcal mol−1 higher selegiline reactivity. Given the similarity with the hydride transfer mechanism during the MAO catalytic activity, these results verify that both rasagiline and selegiline are mechanism-based irreversible inhibitors and offer guidelines in designing new and improved inhibitors, which are all clinically employed in treating a variety of neuropsychiatric and neurodegenerative conditions.

Ferulic Acid Decarboxylase Controls Oxidative Maturation of the Prenylated Flavin Mononucleotide Cofactor.

Prenylated flavin mononucleotide (prFMN) is a recently discovered modified flavin cofactor containing an additional nonaromatic ring, connected to the N5 and C6 atoms. This cofactor underpins reversible decarboxylation catalyzed by members of the widespread UbiD enzyme family and is produced by the flavin prenyltransferase UbiX. Oxidative maturation of the UbiX product prFMNH2 to the corresponding oxidized prFMNiminium is required for ferulic acid decarboxylase (Fdc1; a UbiD-type enzyme) activity. However, it is unclear what role the Fdc1 enzyme plays in this process. Here, we demonstrate that, in the absence of Fdc1, prFMNH2 oxidation by O2 proceeds via a transient semiquinone prFMNradical species and culminates in a remarkably stable prFMN-hydroperoxide species. Neither forms of prFMN are able to support Fdc1 activity. Instead, enzyme activation using O2-mediated oxidation requires prFMNH2 binding prior to oxygen exposure, confirming that UbiD enzymes play a role in O2-mediated oxidative maturation. In marked contrast, alternative oxidants such as potassium ferricyanide support prFMNiminium formation both in solution and in Fdc1.

The theoretical investigation of OH-induced degradation mechanisms of isoproturon.

Herbicides are widely applied in agriculture, which causes emerging concern for contaminating surface water and groundwater. The degradation of isoproturon, being a typical phenylurea herbicide, has been studied much with advanced oxidation processes. However, little information on the detailed degradation mechanism from the theoretical level is available. In the present work, the degradation mechanisms of OH-initiated reactions of isoproturon were studied at the MPWB1K/6-311+G(3df, 2p)//MPWB1K/6-31+G(d, p) level. The calculation results display that H-atom abstraction, ·OH addition, and ·OH substitution pathways are found for ·OH and isoproturon reactions. For H-atom abstractions, the results show that aliphatic H atoms are more easily abstracted by ·OH than the aromatic H atoms, and the pathway R6 has the lowest energy barrier of 6.65kcalmol-1, indicating that H in the -CH3 group attached to the N2 atom could be most favorably abstracted. Six pathways for ·OH addition to the six sites of the phenyl ring are identified with low energy barriers, which are in good accordance with the fact that the additions of ·OH to the phenyl ring were the important steps from experimental results. For ·OH substitution reactions, two pathways with high activation energies are found, and the corresponding products have been also detected from previous experimental studies, suggesting that the substitution reactions could also occur.

Synthesis of 3(2)-phosphonylated thiazolo[3,2-a]oxopyrimidines.

A series of 3(2)-phosphonylated thiazolo[3,2-a]oxopyrimidines was synthesized for the first time by the reactions of chloroethynylphosphonates with unsubstituted and 5(6)-substituted 2-thiouracils. The reaction of chloroethynylphosphonates with 6-substituted 2-thiouracils bearing electron-donor groups (CH3, Ph) proceeded with high regioselectivity involving the cyclization through the N3-nitrogen atom to form new 3-phosphonylated thiazolo[3,2-a]-5-oxopyrimidines with good yield. In the case of unsubstituted and 5-methyl-2-thiouracils, cyclization occurred predominantly through the N1 atom and partially via the N3-nitrogen atom to form a mixture of the corresponding thiazolo[3,2-a]-7- and 5-oxopyrimidines. A dramatic change in the reaction regioselectivity was observed in the case of 6-trifluoromethyl-2-thiouracil that afforded 2- and 3-phosphonylated 5-oxothiazolopyrimidines in a 1:1 ratio.

Synthesis of new arylplatinum complexes containing 2,2′-dipyridylamine; single crystal structure, electrochemical studies and calculation of the kinetic parameters

New aryl-Pt(II) complex, including 2,2′-dipyridylamine (dpya) as a bidentate ligand was obtained through the reaction of [(p-tolyl)2Pt(Me2S)2] with 2,2′-dipyridylamine in a 1:1 stoichiometry. The aryl-Pt(IV) complex was synthesized during the oxidative addition reaction of [Pt(p-tolyl)2dpya] with MeI. In these organoplatinum complexes, dpya was bonded to the Pt center via N2 atoms. The MeI was used as a reagent for investigation of oxidative addition reaction (ox. add) on the Pt(II) center, which led to the formation of Pt(IV) complex with octahedral geometry. It was shown that the synthesized Pt(II) and Pt(IV) complexes contain a 1:1 M:L molar ratio. Moreover, conductivity measurements confirmed the non-electrolyte nature of the platinum complexes. These organoplatinum complexes have been characterized by X-ray crystal structure, 1H NMR, FT-IR, conductometry, elemental analysis and UV/Vis spectroscopy. Single X-ray crystal structure showed the asymmetric unit of the Pt(II) complex included one Pt(II) atom, one 2,2′-dipyridylamine and two p-tolyl groups. Furthermore, oxidative addition reaction of iodomethane with Pt(II) complex at 29, 32, 35 and 38 °C was studied and the enthalpy and entropy of activation, activation energy (Ea) and rate constants were calculated.

Contributions and competition of Mg2+ and K+ in folding and stabilization of the Twister ribozyme.

Native folded and compact intermediate states of RNA typically involve tertiary structures in the presence of divalent ions such as Mg2+ in a background of monovalent ions. In a recent study, we have shown how the presence of Mg2+ impacts the transition from partially unfolded to folded states through a “push-pull” mechanism where the ion both favors and disfavors the sampling of specific phosphate-phosphate interactions. To further understand the ion atmosphere of RNA in folded and partially folded states results from atomistic umbrella sampling and oscillating chemical potential grand canonical Monte Carlo/molecular dynamics (GCMC/MD) simulations are used to obtain atomic-level details of the distributions of Mg2+ and K+ ions around Twister RNA. Results show the presence of 100 mM Mg2+ to lead to increased charge neutralization over that predicted by counterion condensation theory. Upon going from partially unfolded to folded states, overall charge neutralization increases at all studied ion concentrations that, while associated with an increase in the number of direct ion-phosphate interactions, is fully accounted for by the monovalent K+ ions. Furthermore, K+ preferentially interacts with purine N7 atoms of helical regions in partially unfolded states, thereby potentially stabilizing the helical regions. Thus, both secondary helical structures and formation of tertiary structures leads to increased counterion condensation, thereby stabilizing those structural features of Twister. Notably, it is shown that K+ can act as a surrogate for Mg2+ by participating in specific interactions with nonsequential phosphate pairs that occur in the folded state, explaining the ability of Twister to self-cleave at submillimolar Mg2+ concentrations.

The effect of metal alkali cations on the properties of hydrogen bonds in tautomeric forms of adenine – Guanine mismatch

The effect of interactions of Li+, Na+ and K+ cations with two preferred configuration of the A–G mispairs, AantiGanti and AsynGanti, on the geometries and hydrogen bond energies have been studied at the MP2/6–311++G(d,p) level of theory. For each ion type, the most stable complex in AantiGanti and AsynGanti configurations are related to binding cation to N3 atom of guanine and N1 atom of adenine, respectively. The AantiGanti configuration is higher in the absolute values of binding energy than the AsynGanti configuration, indicating that AantiGanti configuration is more stable than AsynGanti ones. The results indicate that the strength of hydrogen bonds depends on the type and position of cations in considered systems. The values of hydrogen bonding energies estimated by the EML formula in AantiGanti mismatch are higher than AsynGanti case. The influences of cations binding in hydrogen bond strength are confirmed by the results of natural bond orbital (NBO) and atoms in molecules (AIM) analyses.

Halido‐bridged Copper(II) Complexes with 1‐tert‐Butyl‐1H‐tetrazole: Crystal Structure and Magnetic Properties

Complex [Cu(tbt)Cl2]n (tbt = 1‐tert‐butyl‐1H‐tetrazole) was prepared by reaction of tbt with copper(II) chloride in solution. According to single‐crystal X‐ray analysis, this complex presents 1D coordination polymer, formed at the expense of double chlorido bridges between neighboring pentacoordinate copper(II) cations. 1‐tert‐Butyl‐1H‐tetrazole acts as monodentate ligand coordinated by CuII cations via the heteroring N4 atoms. The temperature‐dependent magnetic susceptibility measurements of novel complex [Cu(tbt)Cl2]n as well as described previously 1D coordination polymer [Cu(tbt)2Cl2]n, and linear trinuclear complex [Cu3(tbt)6Br6], were carried out. Magnetic studies revealed that the copper(II) ions were weakly ferromagnetically coupled in polymeric copper(II) chloride complexes, whereas complex [Cu3(tbt)6Br6] showed antiferromagnetic coupling.

Synthesis of IrIII Hydrido Complexes by Oxidative Addition of Halogenated Theophylline and Adenine Derivatives.

The IrIII hydrido complexes [1] and [2] have been synthesized by the regioselective oxidative addition of the N7–H bond of 8-halogenotheophyllines to [IrCl(coe)2]2 in the presence of PPh3. The use of dppf in this reaction yielded the bimetallic IrIII/FeII hydrido complexes [3] and [4]. X-ray diffraction studies confirmed that complexes [1]–[4] feature a theophyllinato ligand coordinated to the metal center in the rarely observed, chelating fashion via the N7 and O1 atoms. In addition, 8-bromoadenine reacts with [IrCl(coe)2]2 in the presence of PPh3 to form the IrIII hydrido complex [5] which features one anionic 8-bromoadeninato and one neutral 8-bromoadenine ligand linked by an intramolecular hydrogen bond. Complex [5] was characterized by high-resolution mass spectrometry and an X-ray diffraction analysis but could not be analyzed by nuclear magnetic resonance spectroscopy because of its low solubility.

Crystallographic Analysis of a Copper(II) Complex with bis(4,4′-Ethane-1,2-Diylbis(Azanediyl))-bis(3-(2-(4-Flurophenyl)Hydrazinyl)Pentan-2-One)

A new copper(II) complex with bis(4,4′-(ethane-1,2-diylbis(azanediyl))bis(3-(2-(4-fluorophenyl) hydrazinyl)pentan-2-one) (1) is synthesized and analyzed by single crystal X-ray diffraction. The crystals are monoclinic: a = 11.1340(9) A, b = 11.6716(10) A, c = 18.7797(16) A, β = 94.792(2)°, V = 2431.9(4) A3, space group P21/n, Z = 4, ρcalc = 1.713 mg/m3, R = 0.0695. The environment of the copper atom is formed by four donor nitrogen atoms (N1, N3, N4, N6). These atoms are at the equatorial position. The N6 atom slightly deviates from the middle plane. Phenyl rings are not involved in the coordination. Additional crystallographic data are available from the Cambridge Crystallography Data Center under number CCDC 1907359.

Chemosensing of Guanosine Triphosphate Based on a Fluorescent Dinuclear Zn(II)-Dipicolylamine Complex in Water.

Guanosine triphosphate (GTP) is a key biomarker of multiple cellular processes and human diseases. The new fluorescent dinuclear complex [Zn2(L)(S)][OTf]4, 1 (asymmetric ligand, L = 5,8-Bis{[bis(2-pyridylmethyl)amino] methyl}quinoline, S = solvent, and OTf = triflate anion) was synthesized and studied in-depth as a chemosensor for nucleoside polyphosphates and inorganic anions in pure water. Additions at neutral pH of nucleoside triphosphates, guanosine diphosphate, guanosine monophosphate, and pyrophosphate (PPi) to 1 quench its blue emission (λem = 410 nm) with a pronounced selectivity toward GTP over other anions, including adenosine triphosphate (ATP), uridine triphosphate (UTP), and cytidine triphosphate (CTP). The efficient quenching response by the addition of GTP was observed in the presence of coexisting species in blood plasma and urine with a detection limit of 9.2 μmol L-1. GTP also shows much tighter binding to the receptor 1 on a submicromolar level. On the basis of multiple spectroscopic tools (1H, 31P NMR, UV-vis, and fluorescence) and DFT calculations, the binding mode is proposed through three-point recognition involving the simultaneous coordination of the N7 atom of the guanosine motif and two phosphate groups to the two Zn(II) atoms. Spectroscopic studies, MS-ESI, and DFT suggested that GTP bound to 1 in 1:1 and 2:2 models with high overall binding constants of log β1(1:1) = 6.05 ± 0.01 and log β2 = 10.91 ± 0.03, respectively. The optical change and selectivity are attributed to the efficient binding of GTP to 1 by the combination of a strong electrostatic contribution and synergic effects of coordination bonds. Such GTP selectivity of an asymmetric metal-based receptor in water is still rare.

Multiresponsive Spin Crossover Driven by Rotation of Tetraphenylborate Anion in an Iron(III) Complex

Dynamic molecular materials, which involve mechanical motions in crystals, usually exhibit tunable properties related to conformational polymorphs. Herein, we describe a solvent-free molecular crys...

Ultrathin 1T-MoS2 Nanoplates Induced by Quaternary Ammonium-Type Ionic Liquids on Polypyrrole/Graphene Oxide Nanosheets and Its Irreversible Crystal Phase Transition During Electrocatalytic Nitrogen Reduction.

Ultrathin nanoplates of metastable 1T-MoS2 have been successfully stabilized and uniformly distributed on the surface of n-butyl triethyl ammonium bromide functionalized polypyrrole/graphene oxide (BTAB/PPy/GO) by a very simple hydrothermal method. BTAB as a typical kind of quaternary ammonium-type ionic liquids (ILs) played a crucial role in the formation of the obtained 1T-MoS2/BTAB/PPy/GO. It was covalently linked with PPy/GO and arranged in a highly ordered order at the solid-liquid interface of PPy/GO and H2O due to Coulombic interactions and other intermolecular interactions, which would induce and stabilize ultrathin 1T-MoS2 nanoplates by morphosynthesis. The good electrocatalytic activity toward nitrogen reduction reaction (NRR) with strong durability and good stability can be achieved by 1T-MoS2/BTAB/PPy/GO due to their excellent inorganic/organic hierarchical lamellar micro-/nanostructures. Especially, after the long-term electrocatalysis for NRR at a negative potential, metastable 1T-MoS2 as the catalytic center undergoes two types of irreversible crystal phase transition, which was converted to 1T'-MoS2 and Mo2N, caused by the competitive hydrogen evolution reaction (HER) process and the electrochemical reaction between the electroactive 1T-MoS2 and N2, respectively. The new N-Mo bonding prevents Mo atoms from binding to other N atoms in N2, resulting in the deactivation of the electrocatalysts to NRR after being used for 18 h. Even so, quaternary ammonium-type ILs would induce the crystal structures of transition-metal dichalcogenides (TMDCs), which might provide a new thought for the reasonable design of electrocatalysts based on TMDCs for electrocatalysis.

Hofmeister Series for Metal-Cation-RNA Interactions: The Interplay of Binding Affinity and Exchange Kinetics.

A large variety of physicochemical properties involving RNA depends on the type of metal cation present in solution. In order to gain microscopic insight into the origin of these ion specific effects, we apply molecular dynamics simulations to describe the interactions of metal cations and RNA. For the three most common ion binding sites on RNA, we calculate the binding affinities and exchange rates of eight different mono- and divalent metal cations. Our results reveal that binding sites involving phosphate groups preferentially bind metal cations with high charge density (such as Mg2+) in inner-sphere conformations while binding sites involving N7 or O6 atoms preferentially bind cations with low charge density (such as K+). The binding affinity therefore follows a direct Hofmeister series at the backbone but is reversed at the nucleobases leading to a high selectivity of ion binding sites on RNA. In addition, the exchange rates for cation binding cover almost 5 orders of magnitude, leading to a vastly different time scale for the lifetimes of contact pairs. Taken together, the site-specific binding affinities and the specific lifetime of contact pairs provide the microscopic explanation of ion specific effects observed in a wide variety of macroscopic RNA properties. Finally, combining the results from atomistic simulations with extended Poisson–Boltzmann theory allows us to predict the distribution of metal cations around double-stranded RNA at finite concentrations and to reproduce the results of ion counting experiments with good accuracy.

Probing DNA Stability in High Electric Fields: Electrochemical Melting Analysis

Here we present our results on the electric field-induced melting of surface-bound DNA (i.e. electrochemical melting). In particular, we examine the effects of DNA-binding compounds, such as cisplatin, on the stability of DNA within high electric fields. Cisplatin is an anticancer drug that has been used to successfully treat testicular, ovarian, and bladder cancers, among others [1]. It crosslinks DNA between the N7 atoms of purine bases, resulting in changes in structure and stability, ultimately interfering with vital cellular processes in vivo. Self-assembled monolayers (SAMs) of thiol-modified oligonucleotides on gold electrodes provide selective and sensitive interfaces for the development of chemical and biological sensors [2]. While many transduction mechanisms have been utilized (including electrochemical, optical, and gravimetric) and many analytes targeted (e.g. small DNA-binding molecules, heavy metals, and specific DNA sequences), the unique steric and electrostatic environment of the crowded DNA in the electrical double-layer complicates the behavior of these biosensors [3]. Electrical potentials applied at the DNA-SAM have been shown to modulate the behavior of these monolayers [4]. Here, we utilize the electric field-effect to induce melting of the bound double-stranded DNA, and we monitor the kinetics of the melting process using square wave voltammetry [5]. We find that the effect of cisplatin on the melting behavior depends on the method used to the prepare the monolayer, in particular the surface-coverage and heterogeneity of the resulting layers. In some instances, cisplatin results in a stabilization of the DNA-SAM and in others a destabilization. Significant differences in the resulting melting curves imply that the mode of cisplatin-DNA binding varies depending on the preparation method. This methodology has the potential of (1) providing an electrochemical approach for studying the interaction between DNA and small molecules, and (2) providing a method for indirectly assessing the heterogeneity of DNA-SAMs via electrochemical melting in the presence of cross-linking agents.[1] R. A. Alderden, M. D. Hall, T. W. Hambley, The discovery and development of cisplatin, Journal of chemical education, 83(5), (2006) 728.[2] J. J. Gooding and N. Darwish, The rise of self‐assembled monolayers for fabricating electrochemical biosensors—an interfacial perspective, The Chemical Record, 12, (2012) 92.[3] Gong and R. Levicky, DNA surface hybridization regimes, Proceedings of the National Academy of Sciences, 105, (2008) 5301.[4] U. Rant, K. Arinaga, S. Fujita, N. Yokoyama, G. Abstreiter, M. Tornow, Electrical manipulation of oligonucleotides grafted to charged surfaces, Organic & Biomolecular Chemistry 4 (2006) 3448.[5] D. Ho, W. Hetrick, N. Le, A. Chin, R. M. West, Electric Field Induced DNA Melting with Detection by Square Wave Voltammetry, Journal of the Electrochemical Society, 166, (2019) B236.

Small-Molecule Inhibitors of METTL3, the Major Human Epitranscriptomic Writer.

The RNA methylase METTL3 catalyzes the transfer of a methyl group from the cofactor S-adenosyl-L-methionine (SAM) to the N6 atom of adenine. We have screened a library of 4000 analogues and derivatives of the adenosine moiety of SAM by high-throughput docking into METTL3. Two series of adenine derivatives were identified in silico, and the binding mode of six of the predicted inhibitors was validated by protein crystallography. Two compounds, one for each series, show good ligand efficiency. We propose a route for their further development into potent and selective inhibitors of METTL3.

Covalent Modification of the Flavin in Proline Dehydrogenase by Thiazolidine-2-Carboxylate.

Proline dehydrogenase (PRODH) catalyzes the first step of proline catabolism, the FAD-dependent 2-electron oxidation of l-proline to Δ1-pyrroline-5-carboxylate. PRODH has emerged as a possible cancer therapy target, and thus the inhibition of PRODH is of interest. Here we show that the proline analogue thiazolidine-2-carboxylate (T2C) is a mechanism-based inactivator of PRODH. Structures of the bifunctional proline catabolic enzyme proline utilization A (PutA) determined from crystals grown in the presence of T2C feature strong electron density for a 5-membered ring species resembling l-T2C covalently bound to the N5 of the FAD in the PRODH domain. The modified FAD exhibits a large butterfly bend angle, indicating that the FAD is locked into the 2-electron reduced state. Reduction of the FAD is consistent with the crystals lacking the distinctive yellow color of the oxidized enzyme and stopped-flow kinetic data showing that T2C is a substrate for the PRODH domain of PutA. A mechanism is proposed in which PRODH catalyzes the oxidation of T2C at the C atom adjacent to the S atom of the thiazolidine ring (C5). Then, the N5 atom of the reduced FAD attacks the C5 of the oxidized T2C species, resulting in the covalent adduct observed in the crystal structure. To our knowledge, this is the first report of T2C inactivating (or inhibiting) PRODH or any other flavoenzyme. These results may inform the design of new mechanism-based inactivators of PRODH for use as chemical probes to study the roles of proline metabolism in cancer.

Synthesis and structure of copper(II) complexes with 1-iso-propyl-1Н-1,2,4-triazole

A novel facile method for the synthesis of 1-iso-propyl-1H-1,2,4-triazole (L) is described. This method is based on alkylation of 1,2,4-triazole with isopropyl alcohol in sulfuric acid media. It allows to synthesize the target product selectively with a yield of near 98 %. New coordination compounds [CuL2(Н2О)2Cl2] and [СuL4Cl2] were synthesized by the interaction of 1-iso-propyl-1H-1,2,4-triazole with copper(II) chloride dihydrate. Composition and structure of prepared complexes were studied by elemental analysis, X-ray diffraction analysis and IR spectroscopy. Both coordination compounds were found to be mononuclear complexes with octahedral coordination of copper atoms. Ligand L shows monodentate coordination through the triazole ring N4 atom. The analysis of the changes observed in the IR-spectrum of L under coordination with CuII atom was carried out. It was shown that IR spectroscopy can be used in order to study some structural peculiarities of azole complexes, in particular presence of bounded or coordinated water molecules and hydrogen bonds as well as localization of coordination bonds.

Copper-assisted desulfurization of 1-R-tetrazole-5-thiols under complexation

The interaction of 1-R-tetrazole-5-thiols with copper(II) chloride in solution was found to yield crystalline tetrazole complexes [CuCl2L2]n (L is 1-R-tetrazole, R = Me, Et, Bu) and [CuCl2L2]n·nMeCN (L is 1-phenyltetrazole). The observed transformation of 1-R-tetrazole-5-thiols into 1-R-tetrazoles presents the first examples of desulfurization of tetrazole-5-thiols under complexation. A possible pathway of desulfurization of 1-R-tetrazole-5-thiols is proposed. It includes initial oxidation of tetrazole-5-thiols by copper(II) ions into bis(tetrazol-5-yl)disulfanes, followed by copper-assisted oxidation by air oxygen. Obtained complexes [CuCl2L2]n and [CuCl2L2]n·nMeCN were found to be coordination polymers, 2D and 1D, respectively. In all them, 1-R-tetrazoles act as monodentate ligands coordinated to the metal via the tetrazole ring N4 atom, whereas chlorine atoms provide bidentate bridging coordination to generate polymeric structure.

Cyclic di-GMP in Streptomycetes: A New Conformation, New Binding Mode, New Receptor, and a New Mechanism to Control Cell Development.

A recent paper by Gallagher etal. (2020) demonstrates that c-di-GMP controls spore formation in Streptomyces venezuelae through sequestering the sporulation sigma factor σWhiG and presents the crystal structure of a ternary complex between c-di-GMP, σWhiG, and its anti-sigma factor, RsiG.