Structural basis for high‐affinity volatile anesthetic binding in a natural 4‐helix bundle protein

Antagonism of propofol anesthesia by alkyl-fluorobenzene derivatives

Despite their frequent use across many clinical settings, general anesthetics are medications with lethal side effects and no reversal agents. A fluorinated analogue of propofol has previously been shown to antagonize propofol anesthesia in tadpoles and zebrafish, but little further investigation of this class of molecules as anesthetic antagonists has been conducted. A 13-member library of alkyl-fluorobenzene derivatives was tested in an established behavioral model of anesthesia in zebrafish at 5 days post fertilization. These compounds were examined for their ability to antagonize propofol and two volatile anesthetics, as well as their interaction with the anesthetic-binding model protein apoferritin. Two compounds provided significant antagonism of propofol, and when combined, were synergistic, suggesting more than one antagonist sensitive target site. These compounds did not antagonize the volatile anesthetics, indicating some selectivity amongst general anesthetics. For the compounds with the most antagonistic potency, similarities in structure and binding to apoferritin may be suggestive of competitive antagonism; however, this was not supported by a Schild analysis. This is consistent with multiple targets contributing to general anesthesia, but whether these are physiologic antagonists or are antagonists at only some subset of the many anesthetic potential targets remains unclear, and will require additional investigation.

Antagonism of Propofol Anesthesia by Alkyl-fluorobenzene Derivatives

Despite their frequent use across many clinical settings, general anesthetics are medications with lethal side effects and no reversal agents. A fluorinated analogue of propofol has previously been shown to antagonize propofol anesthesia in tadpoles and zebrafish, but little further investigation of this class of molecules as anesthetic antagonists has been conducted. A 13-member library of alkyl-fluorobenzene derivatives was tested in an established behavioral model of anesthesia in zebrafish at 5 days post fertilization. These compounds were examined for their ability to antagonize propofol and two volatile anesthetics, as well as their binding to the anesthetic-binding model protein apoferritin. The two compounds demonstrating highest antagonistic potency were found to bind apoferritin in a manner similar to propofol. Selected compounds did not show antagonism of volatile anesthetics, indicating some selectivity of this antagonism. Similarities in structure and binding to apoferritin as well as a Schild analysis are suggestive of competitive antagonism, but like the anesthetics, the potential mechanism(s) of these antagonists will require further mechanistic investigation.

An In Silico Investigation of the Molecular Interactions between Volatile Anesthetics and Actin

Volatile anesthetics (VAs) are medicinal chemistry compounds commonly used to enable surgical procedures for patients who undergo painful treatments and can be partially or fully sedated, remaining in an unconscious state during the operation. The specific molecular mechanism of anesthesia is still an open issue, but scientific evidence supports the hypothesis of the involvement of both putative hydrophobic cavities in membrane receptors as binding pockets and interactions between anesthetics and cytoplasmic proteins. Previous studies demonstrated the binding of VAs to tubulin. Since actin is the other major component of the cytoskeleton, this study involves an investigation of its interactions with four major anesthetics: halothane, isoflurane, sevoflurane, and desflurane. Molecular docking was implemented using the Molecular Operating Environment (MOE) software (version 2022.02) and applied to a G-actin monomer, extrapolating the relative binding affinities and root-mean-square deviation (RMSD) values. A comparison with the F-actin was also made to assess if the generally accepted idea about the enhanced F-to-G-actin transformation during anesthesia is warranted. Overall, our results confirm the solvent-like behavior of anesthetics, as evidenced by Van der Waals interactions as well as the relevant hydrogen bonds formed in the case of isoflurane and sevoflurane. Also, a comparison of the interactions of anesthetics with tubulin was made. Finally, the short- and long-term effects of anesthetics are discussed for their possible impact on the occurrence of mental disorders.

Competition between electrostatic interactions and halogen bonding in the protein-ligand system: structural and thermodynamic studies of 5,6-dibromobenzotriazole-hCK2α complexes

CK2 is a member of the CMGC group of eukaryotic protein kinases and a cancer drug target. It can be efficiently inhibited by halogenated benzotriazoles and benzimidazoles. Depending on the scaffold, substitution pattern, and pH, these compounds are either neutral or anionic. Their binding poses are dictated by a hydrophobic effect (desolvation) and a tug of war between a salt bridge/hydrogen bond (to K68) and halogen bonding (to E114 and V116 backbone oxygens). Here, we test the idea that binding poses might be controllable by pH for ligands with near-neutral pK_a, using the conditionally anionic 5,6-DBBt and constitutively anionic TBBt as our models. We characterize the binding by low-volume Differential Scanning Fluorimetry (nanoDSF), Isothermal Calorimetry (ITC), Hydrogen/Deuterium eXchange (HDX), and X-ray crystallography (MX). The data indicate that the ligand pose away from the hinge dominates for the entire tested pH range (5.5-8.5). The insensitivity of the binding mode to pH is attributed to the perturbation of ligand pK_a upon binding that keeps it anionic in the ligand binding pocket at all tested pH values. However, a minor population of the ligand, detectable only by HDX, shifts towards the hinge in acidic conditions. Our findings demonstrate that electrostatic (ionic) interactions predominate over halogen bonding.

Influence of Krypton Gas Nanobubbles on the Activity of Pepsin

The fact that biologically inert gases can significantly affect the biological function of proteins still lacks a full understanding because they are usually chemically stable and weakly absorbed by biological molecules. Recently, nanobubbles were proposed to play an important role in the activity of a protein (Scientific reports 2013, 3; Scientific reports 2017, 7, 10176). In this study, we developed a controllable method to produce high-concentration krypton (Kr) gas nanobubbles in pure water and measured the concentration influence of those Kr nanobubbles on pepsin protein activity. By combining high-sensitivity synchrotron radiation X-ray fluorescence techniques with a nanoparticle tracking analysis technology, we provided strong evidence that the observed "nanoparticles" were indeed Kr nanobubbles. Activity measurements showed that the activity would be inhibited by the existence of Kr nanobubbles and could be recovered by degassing. More importantly, the inhibition extent of pepsin activity was dominated by the number of nanobubbles in solution. More nanobubbles would cause more inhibition of pepsin activity. Furthermore, the structures of pepsin could be changed by nanobubbles, which might be the reason for inhabitation of activity. Our results would provide a further understanding of the mechanisms of the biological effects of inert gases.

Molecular Bases for Anesthetic Agents: Halothane as a Halogen- and Hydrogen-Bond Donor

Although instrumental for optimizing their pharmacological activity, a molecular understanding of the preferential interactions given by volatile anesthetics is quite poor. This paper confirms the ability of halothane to work as a hydrogen-bond (HB) donor and gives the first experimental proof that halothane also works as a halogen-bond (HaB) donor in the solid state and in solution. A halothane/hexamethylphosphortriamide co-crystal is described and its single-crystal X-ray structure shows short HaBs between bromine, or chlorine, and the phosphoryl oxygen. New UV/Vis absorption bands appear upon addition of diazabicyclooctane and tetra(n-butyl)ammonium iodide to halothane solutions, indicating that nitrogen atoms and anions may mediate the HaB-driven binding processes involving halothane as well. The ability of halothane to work as a bidentate/tridentate tecton by acting as a HaB and HB donor gives an atomic rationale for the eudismic ratio shown by this agent.

Investigation of Anesthetic-Protein Interactions by a Thermodynamic Approach

Anesthetics can interact with a wide variety of proteins in the body, including ion channels and alter their activity, but little is known about the molecular mechanisms of the interactions responsible for the functional activity. Characterization of the nature of anesthetic-protein interactions therefore is important and requires the complete analysis of the binding energetics. Isothermal titration calorimetry (ITC) is the only technique that allows quantitative determination of all thermodynamic parameters, including the equilibrium binding constant (K_B), the standard Gibbs free energy change (ΔG), the enthalpy change (ΔH), the entropy change (ΔS), heat capacity change (ΔC_p), and stoichiometry (n) of the reaction. ITC does not require any labeling or modification of the interacting partners analyzed and can be performed in solution with small amounts of reagents. In this chapter we describe the general properties of the ITC method, highlighting some critical aspects of experimental planning and data analysis, with practical application to anesthetic-protein interactions.

Near-Infrared Fluorescent Dye-Decorated Nanocages to Form Grenade-like Nanoparticles with Dual Control Release for Photothermal Theranostics and Chemotherapy

Recently, nanoparticles (NPs) have been widely investigated for delivery of anticancer drugs. Here, a dual control drug-release modality was developed that uses naturally occurring protein apoferritin loaded with doxorubicin (DOX) and ADS-780 near-infrared (NIR) fluorescent dye-decorated NPs (ADNIR NPs). ADNIR NPs act as a grenade to detonate the targeted tumor site following laser irradiation (photothermal therapy, PTT) and explode into cluster warheads (apoferritin-loaded DOX nanocages, AF-DOX NCs) that further destroy the tumor cells (chemotherapy). Light was shown to disrupt the grenade-like structure of NPs to release AF-DOX NCs as well as DOX from NCs in low-pH intercellular environments. In vitro and in vivo studies showed that the structure of AF-DOX NCs was disassembled to release DOX, which then killed the cancer cells in organelles with acidic environments. In vivo studies showed that the ADNIR NP-decorated with NIR dye facilitated tracking of the accumulated NPs at the tumor site using an IVIS imaging system. Overall, targeted ADNIR NPs with dual-release mechanisms were developed for use in photothermal theranostic and chemotherapy. This modality has high potential for application in cancer treatment and clinical translation for drug delivery and imaging.

Insights Into Receptor-Based Anesthetic Pharmacophores and Anesthetic-Protein Interactions

General anesthetics are thought to allosterically bind and potentiate the inhibitory currents of the GABA_A receptor through drug-specific binding sites. The physiologically relevant isoform of the GABA_A receptor is a transmembrane ligand-gated ion channel consisting of five subunits (γ-α-β-α-β linkage) symmetrically arranged around a central chloride-conducting pore. Although the exact molecular structure of this heteropentameric GABA_A receptor remains unknown, molecular modeling has allowed significant advancements in understanding anesthetic binding and action. Using the open-channel conformations of the homologous glycine and glutamate-gated chloride receptors as templates, a homology model of the GABA_A receptor was constructed using the Discovery Studio computational chemistry software suite. Consensus structural alignment of the homology templates allowed for the construction of a three-dimensional heteropentameric GABA_A receptor model with (γ₂-β₃-α₁-β₃-α₁) subunit linkage. An anesthetic binding site was identified within the transmembrane α/β intersubunit space by the convergence of three residues shown to be essential for anesthetic activity in previous studies with mutant mice (β₃-N265, β₃-M286, α₁-L232). Propofol derivatives docked into this binding site showed log-linear correlation with experimentally derived GABA_A receptor potentiation (EC₅₀) values, suggesting this binding site may be important for receptor activation. The receptor-based pharmacophore was analyzed with surface maps displaying the predominant anesthetic-protein interactions, revealing an amphiphilic binding cavity incorporating the three residues involved in anesthetic modulation. Quantum mechanics calculations of the bonding patterns found in complementary high-resolution receptor systems further elucidated the complex nature of anesthetic-protein interactions.

Structural Analysis of Anesthetics in Complex with Soluble Proteins

Anesthetics interact with a broad range of different targets, including both soluble and membrane-bound proteins. Understanding these interactions at the molecular level requires detailed structural knowledge of anesthetic-protein complexes, and one of the most productive routes to such knowledge is X-ray crystallography. In this chapter we discuss the application of this technique to the analysis of complexes of anesthetics with soluble proteins. The model protein apoferritin is highlighted, and protocols are presented for obtaining diffraction-quality crystals of this protein in complex with different general anesthetics.

Shedding Light on Anesthetic Mechanisms: Application of Photoaffinity Ligands

Anesthetic photoaffinity ligands have had an increasing presence within anesthesiology research. These ligands mimic parent general anesthetics and allow investigators to study anesthetic interactions with receptors and enzymes; identify novel targets; and determine distribution within biological systems. To date, nearly all general anesthetics used in medicine have a corresponding photoaffinity ligand represented in the literature. In this review, we examine all aspects of the current methodologies, including ligand design, characterization, and deployment. Finally we offer points of consideration and highlight the future outlook as more photoaffinity ligands emerge within the field.

Unsaturated Long-Chain Fatty Acids Are Preferred Ferritin Ligands That Enhance Iron Biomineralization

Ferritin is a ubiquitous nanocage protein, which can accommodate up to thousands of iron atoms inside its cavity. Aside from its iron storage function, a new role as a fatty acid binder has been proposed for this protein. The interaction of apo horse spleen ferritin (HoSF) with a variety of lipids has been here investigated through NMR spectroscopic ligand-based experiments, to provide new insights into the mechanism of ferritin-lipid interactions, and the link with iron mineralization. 1D ¹ H, diffusion (DOSY) and saturation-transfer difference (STD) NMR experiments provided evidence for a stronger interaction of ferritin with unsaturated fatty acids compared to saturated fatty acids, detergents, and bile acids. Mineralization assays showed that oleate c aused the most efficient increase in the initial rate of iron oxidation, and the highest formation of ferric species in HoSF. The comprehension of the factors inducing a faster biomineralization is an issue of the utmost importance, given the association of ferritin levels with metabolic syndromes, such as insulin resistance and diabetes, characterized by fatty acid concentration dysregulation. The human ferritin H-chain homopolymer (HuHF), featuring ferroxidase activity, was also tested for its fatty acid binding capabilities. Assays show that oleate can bind with high affinity to HuHF, without altering the reaction rates at the ferroxidase site.

Photoaffinity Ligand for the Inhalational Anesthetic Sevoflurane Allows Mechanistic Insight into Potassium Channel Modulation

Sevoflurane is a commonly used inhaled general anesthetic. Despite this, its mechanism of action remains largely elusive. Compared to other anesthetics, sevoflurane exhibits distinct functional activity. In particular, sevoflurane is a positive modulator of voltage-gated Shaker-related potassium channels (K_v1.x), which are key regulators of action potentials. Here, we report the synthesis and validation of azisevoflurane, a photoaffinity ligand for the direct identification of sevoflurane binding sites in the K_v1.2 channel. Azisevoflurane retains major sevoflurane protein binding interactions and pharmacological properties within in vivo models. Photoactivation of azisevoflurane induces adduction to amino acid residues that accurately reported sevoflurane protein binding sites in model proteins. Pharmacologically relevant concentrations of azisevoflurane analogously potentiated wild-type K_v1.2 and the established mutant K_v1.2 G329T. In wild-type K_v1.2 channels, azisevoflurane photolabeled Leu317 within the internal S4-S5 linker, a vital helix that couples the voltage sensor to the pore region. A residue lining the same binding cavity was photolabeled by azisevoflurane and protected by sevoflurane in the K_v1.2 G329T. Mutagenesis of Leu317 in WT K_v1.2 abolished sevoflurane voltage-dependent positive modulation. Azisevoflurane additionally photolabeled a second distinct site at Thr384 near the external selectivity filter in the K_v1.2 G329T mutant. The identified sevoflurane binding sites are located in critical regions involved in gating of K_v channels and related ion channels. Azisevoflurane has thus emerged as a new tool to discover inhaled anesthetic targets and binding sites and investigate contributions of these targets to general anesthesia.

Clinical concentrations of chemically diverse general anesthetics minimally affect lipid bilayer properties

General anesthetics have revolutionized medicine by facilitating invasive procedures, and have thus become essential drugs. However, detailed understanding of their molecular mechanisms remains elusive. A mechanism proposed over a century ago involving unspecified interactions with the lipid bilayer known as the unitary lipid-based hypothesis of anesthetic action, has been challenged by evidence for direct anesthetic interactions with a range of proteins, including transmembrane ion channels. Anesthetic concentrations in the membrane are high (10-100 mM), however, and there is no experimental evidence ruling out a role for the lipid bilayer in their ion channel effects. A recent hypothesis proposes that anesthetic-induced changes in ion channel function result from changes in bilayer lateral pressure that arise from partitioning of anesthetics into the bilayer. We examined the effects of a broad range of chemically diverse general anesthetics and related nonanesthetics on lipid bilayer properties using an established fluorescence assay that senses drug-induced changes in lipid bilayer properties. None of the compounds tested altered bilayer properties sufficiently to produce meaningful changes in ion channel function at clinically relevant concentrations. Even supra-anesthetic concentrations caused minimal bilayer effects, although much higher (toxic) concentrations of certain anesthetic agents did alter lipid bilayer properties. We conclude that general anesthetics have minimal effects on bilayer properties at clinically relevant concentrations, indicating that anesthetic effects on ion channel function are not bilayer-mediated but rather involve direct protein interactions.

The halogen bonding proclivity of the ortho-methoxy–hydroxy group in cocrystals of o-vanillin imines and diiodotetrafluoro-benzenes

Novel halogen bondedo-hydroxy imine cocrystals with 1,2-, 1,3- and 1,4-diiodotetrafluorobenzene have been synthesized. We present an insight into the halogen bond acceptor potential of theortho-methoxy–hydroxy group of theo-vanillin moiety.

Chiral Alkyl Halides: Underexplored Motifs in Medicine

While alkyl halides are valuable intermediates in synthetic organic chemistry, their use as bioactive motifs in drug discovery and medicinal chemistry is rare in comparison. This is likely attributable to the common misconception that these compounds are merely non-specific alkylators in biological systems. A number of chlorinated compounds in the pharmaceutical and food industries, as well as a growing number of halogenated marine natural products showing unique bioactivity, illustrate the role that chiral alkyl halides can play in drug discovery. Through a series of case studies, we demonstrate in this review that these motifs can indeed be stable under physiological conditions, and that halogenation can enhance bioactivity through both steric and electronic effects. Our hope is that, by placing such compounds in the minds of the chemical community, they may gain more traction in drug discovery and inspire more synthetic chemists to develop methods for selective halogenation.

A Novel Bifunctional Alkylphenol Anesthetic Allows Characterization of γ-Aminobutyric Acid, Type A (GABAA), Receptor Subunit Binding Selectivity in Synaptosomes

Propofol, an intravenous anesthetic, is a positive modulator of the GABAA receptor, but the mechanistic details, including the relevant binding sites and alternative targets, remain disputed. Here we undertook an in-depth study of alkylphenol-based anesthetic binding to synaptic membranes. We designed, synthesized, and characterized a chemically active alkylphenol anesthetic (2-((prop-2-yn-1-yloxy)methyl)-5-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenol, AziPm-click (1)), for affinity-based protein profiling (ABPP) of propofol-binding proteins in their native state within mouse synaptosomes. The ABPP strategy captured ∼4% of the synaptosomal proteome, including the unbiased capture of five α or β GABAA receptor subunits. Lack of γ2 subunit capture was not due to low abundance. Consistent with this, independent molecular dynamics simulations with alchemical free energy perturbation calculations predicted selective propofol binding to interfacial sites, with higher affinities for α/β than γ-containing interfaces. The simulations indicated hydrogen bonding is a key component leading to propofol-selective binding within GABAA receptor subunit interfaces, with stable hydrogen bonds observed between propofol and α/β cavity residues but not γ cavity residues. We confirmed this by introducing a hydrogen bond-null propofol analogue as a protecting ligand for targeted-ABPP and observed a lack of GABAA receptor subunit protection. This investigation demonstrates striking interfacial GABAA receptor subunit selectivity in the native milieu, suggesting that asymmetric occupancy of heteropentameric ion channels by alkylphenol-based anesthetics is sufficient to induce modulation of activity.

Is conformation a fundamental descriptor in QSAR? A case for halogenated anesthetics

An intriguing question in 3D-QSAR lies on which conformation(s) to use when generating molecular descriptors (MD) for correlation with bioactivity values. This is not a simple task because the bioactive conformation in molecule data sets is usually unknown and, therefore, optimized structures in a receptor-free environment are often used to generate the MD´s. In this case, a wrong conformational choice can cause misinterpretation of the QSAR model. The present computational work reports the conformational analysis of the volatile anesthetic isoflurane (2-chloro-2-(difluoromethoxy)-1,1,1-trifluoroethane) in the gas phase and also in polar and nonpolar implicit and explicit solvents to show that stable minima (ruled by intramolecular interactions) do not necessarily coincide with the bioconformation (ruled by enzyme induced fit). Consequently, a QSAR model based on two-dimensional chemical structures was built and exhibited satisfactory modeling/prediction capability and interpretability, then suggesting that these 2D MD´s can be advantageous over some three-dimensional descriptors.

The importance of eukaryotic ferritins in iron handling and cytoprotection

Ferritins, the main intracellular iron storage proteins, have been studied for over 60 years, mainly focusing on the mammalian ones. This allowed the elucidation of the structure of these proteins and the mechanisms regulating their iron incorporation and mineralization. However, ferritin is present in most, although not all, eukaryotic cells, comprising monocellular and multicellular invertebrates and vertebrates. The aim of this review is to provide an update on the general properties of ferritins that are common to various eukaryotic phyla (except plants), and to give an overview on the structure, function and regulation of ferritins. An update on the animal models that were used to characterize H, L and mitochondrial ferritins is also provided. The data show that ferritin structure is highly conserved among different phyla. It exerts an important cytoprotective function against oxidative damage and plays a role in innate immunity, where it also contributes to prevent parenchymal tissue from the cytotoxicity of pro-inflammatory agonists released by the activation of the immune response activation. Less clear are the properties of the secretory ferritins expressed by insects and molluscs, which may be important for understanding the role played by serum ferritin in mammals.

The Halogen Bond

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

Insights into the Nature of Anesthetic-Protein Interactions: An ONIOM Study

Anesthetics have been employed widely to relieve surgical suffering, but their mechanism of action is not yet clear. For over a century, the mechanism of anesthesia was previously thought to be via lipid bilayer interactions. In the present work, a rigorous three-layer ONIOM(M06-2X/6-31+G*:PM6:AMBER) method was utilized to investigate the nature of interactions between several anesthetics and actual protein binding sites. According to the calculated structural features, interaction energies, atomic charges, and electrostatic potential surfaces, the amphiphilic nature of anesthetic-protein interactions was demonstrated for both inhalational and injectable anesthetics. The existence of hydrogen and halogen bonding interactions between anesthetics and proteins was clearly identified, and these interactions served to assist ligand recognition and binding by the protein. Within all complexes of inhalational or injectable anesthetics, the polarization effects play a dominant role over the steric effects and induce a significant asymmetry in the otherwise symmetric atomic charge distributions of the free ligands in vacuo. This study provides new insight into the mechanism of action of general anesthetics in a more rigorous way than previously described. Future rational design of safer anesthetics for an aging and more physiologically vulnerable population will be predicated on this greater understanding of such specific interactions.

Direct Pore Binding as a Mechanism for Isoflurane Inhibition of the Pentameric Ligand-gated Ion Channel ELIC

Pentameric ligand-gated ion channels (pLGICs) are targets of general anesthetics, but molecular mechanisms underlying anesthetic action remain debatable. We found that ELIC, a pLGIC from Erwinia chrysanthemi, can be functionally inhibited by isoflurane and other anesthetics. Structures of ELIC co-crystallized with isoflurane in the absence or presence of an agonist revealed double isoflurane occupancies inside the pore near T237(6′) and A244(13′). A pore-radius contraction near the extracellular entrance was observed upon isoflurane binding. Electrophysiology measurements with a single-point mutation at position 6′ or 13′ support the notion that binding at these sites renders isoflurane inhibition. Molecular dynamics simulations suggested that isoflurane binding was more stable in the resting than in a desensitized pore conformation. This study presents compelling evidence for a direct pore-binding mechanism of isoflurane inhibition, which has a general implication for inhibitory action of general anesthetics on pLGICs.

Structural comparisons of ligand-gated ion channels in open, closed, and desensitized states identify a novel propofol-binding site on mammalian γ-aminobutyric acid type A receptors

BACKGROUND

Most anesthetics, particularly intravenous agents such as propofol and etomidate, enhance the actions of the neurotransmitter γ-aminobutyric acid (GABA) at the GABA type A receptor. However, there is no agreement as where anesthetics bind to the receptor. A novel approach would be to identify regions on the receptor that are state-dependent, which would account for the ability of anesthetics to affect channel opening by binding differentially to the open and closed states.

METHODS

The open and closed structures of the GABA type A receptor homologues Gloeobacter ligand-gated ion channel and glutamate-gated chloride channel were compared, and regions in the channels that move on channel opening and closing were identified. Docking calculations were performed to investigate possible binding of propofol to the GABA type A β3 homomer in this region.

RESULTS

A comparison between the open and closed states of the Gloeobacter ligand-gated ion channel and glutamate-gated chloride channel channels identified a region at the top of transmembrane domains 2 and 3 that shows maximum movement when the channels transition between the open and closed states. Docking of propofol into the GABA type A β3 homomer identified two putative binding cavities in this same region, one with a high affinity and one with a lower affinity. Both cavities were adjacent to a histidine residue that has been photolabeled by a propofol analog, and both sites would be disrupted on channel closing.

CONCLUSIONS

These calculations support the conclusion of a recent photolabeling study that propofol acts at a site at the interface between the extracellular and transmembrane domains, close to the top of transmembrane domain 2.

Role for the propofol hydroxyl in anesthetic protein target molecular recognition

Propofol is a widely used intravenous general anesthetic. We synthesized 2-fluoro-1,3-diisopropylbenzene, a compound that we call "fropofol", to directly assess the significance of the propofol 1-hydroxyl for pharmacologically relevant molecular recognition in vitro and for anesthetic efficacy in vivo. Compared to propofol, fropofol had a similar molecular volume and only a small increase in hydrophobicity. Isothermal titration calorimetry and competition assays revealed that fropofol had higher affinity for a protein site governed largely by van der Waals interactions. Within another protein model containing hydrogen bond interactions, propofol demonstrated higher affinity. In vivo, fropofol demonstrated no anesthetic efficacy, but at high concentrations produced excitatory activity in tadpoles and mice; fropofol also antagonized propofol-induced hypnosis. In a propofol protein target that contributes to hypnosis, α1β2γ2L GABAA receptors, fropofol demonstrated no significant effect alone or on propofol positive allosteric modulation of the ion channel, suggesting an additional requirement for the 1-hydroxyl within synaptic GABAA receptor site(s). However, fropofol caused similar adverse cardiovascular effects as propofol by a dose-dependent depression of myocardial contractility. Our results directly implicate the propofol 1-hydroxyl as contributing to molecular recognition within protein targets leading to hypnosis, but not necessarily within protein targets leading to side effects of the drug.

Thermodynamics parameters for binding of halogenated benzotriazole inhibitors of human protein kinase CK2α

The interaction of human CK2α (hCK2α) with nine halogenated benzotriazoles, TBBt and its analogues representing all possible patterns of halogenation on the benzene ring of benzotriazole, was studied by biophysical methods. Thermal stability of protein-ligand complexes, monitored by calorimetric (DSC) and optical (DSF) methods, showed that the increase in the mid-point temperature for unfolding of protein-ligand complexes (i.e. potency of ligand binding to hCK2α) follow the inhibitory activities determined by biochemical assays. The dissociation constant for the ATP-hCK2α complex was estimated with the aid of microscale thermophoresis (MST) as 4.3±1.8 μM, and MST-derived dissociation constants determined for halogenated benzotriazoles, when converted according to known ATP concentrations, perfectly reconstruct IC50 values determined by the biochemical assays. Ligand-dependent quenching of tyrosine fluorescence, together with molecular modeling and DSC-derived heats of unfolding, support the hypothesis that halogenated benzotriazoles bind in at least two alternative orientations, and those that are efficient hCK2α inhibitors bind in the orientation which TBBt adopts in its complex with maize CK2α. DSC-derived apparent heat for ligand binding (ΔΔHbind) is driven by intermolecular electrostatic interactions between Lys68 and the triazole ring of the ligand, as indicated by a good correlation between ΔΔHbind and ligand pKa. Overall results, additionally supported by molecular modeling, confirm that a balance of hydrophobic and electrostatic interactions contribute predominantly (~40 kJ/mol), relative to possible intermolecular halogen/hydrogen bonding (less than 10 kJ/mol), in binding of halogenated benzotriazoles to the ATP-binding site of hCK2α. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases.

Volatile anesthetics inhibit sodium channels without altering bulk lipid bilayer properties

Although general anesthetics are clinically important and widely used, their molecular mechanisms of action remain poorly understood. Volatile anesthetics such as isoflurane (ISO) are thought to alter neuronal function by depressing excitatory and facilitating inhibitory neurotransmission through direct interactions with specific protein targets, including voltage-gated sodium channels (Na(v)). Many anesthetics alter lipid bilayer properties, suggesting that ion channel function might also be altered indirectly through effects on the lipid bilayer. We compared the effects of ISO and of a series of fluorobenzene (FB) model volatile anesthetics on Na(v) function and lipid bilayer properties. We examined the effects of these agents on Na(v) in neuronal cells using whole-cell electrophysiology, and on lipid bilayer properties using a gramicidin-based fluorescence assay, which is a functional assay for detecting changes in lipid bilayer properties sensed by a bilayer-spanning ion channel. At clinically relevant concentrations (defined by the minimum alveolar concentration), both the FBs and ISO produced prepulse-dependent inhibition of Na(v) and shifted the voltage dependence of inactivation toward more hyperpolarized potentials without affecting lipid bilayer properties, as sensed by gramicidin channels. Only at supra-anesthetic (toxic) concentrations did ISO alter lipid bilayer properties. These results suggest that clinically relevant concentrations of volatile anesthetics alter Na(v) function through direct interactions with the channel protein with little, if any, contribution from changes in bulk lipid bilayer properties. Our findings further suggest that changes in lipid bilayer properties are not involved in clinical anesthesia.

Characterization of a computationally designed water-soluble human μ-opioid receptor variant using available structural information

BACKGROUND

The recent X-ray crystal structure of the murine μ-opioid receptor (MUR) allowed the authors to reengineer a previously designed water-soluble variant of the transmembrane portion of the human MUR (wsMUR-TM).

METHODS

The new variant of water-soluble MUR (wsMUR-TM_v2) was engineered based on the murine MUR crystal structure. This novel variant was expressed in Escherichia coli and purified. The properties of the receptor were characterized and compared with those of wsMUR-TM.

RESULTS

Seven residues originally included for mutation in the design of the wsMUR-TM were reverted to their native identities. wsMUR-TM_v2 contains 16% mutations of the total sequence. It was overexpressed and purified with high yield. Although dimers and higher oligomers were observed to form over time, the wsMUR-TM_v2 stayed predominantly monomeric at concentrations as high as 7.5 mg/ml in buffer within a 2-month period. Its secondary structure was predominantly helical and comparable with those of both the original wsMUR-TM variant and the native MUR. The binding affinity of wsMUR-TM_v2 for naltrexone (K(d) approximately 70 nM) was in close agreement with that for wsMUR-TM. The helical content of wsMUR-TM_v2 decreased cooperatively with increasing temperature, and the introduction of sucrose was able to stabilize the protein.

CONCLUSIONS

A novel functional wsMUR-TM_v2 with only 16% mutations was successfully engineered, expressed in E. coli, and purified based on information from the crystal structure of murine MUR. This not only provides a novel alternative tool for MUR studies in solution conditions but also offers valuable information for protein engineering and structure-function relations.

Biomolecular halogen bonds

Halogens are atypical elements in biology, but are common as substituents in ligands, including thyroid hormones and inhibitors, which bind specifically to proteins and nucleic acids. The short-range, stabilizing interactions of halogens - now seen as relatively common in biology - conform generally to halogen bonds characterized in small molecule systems and as described by the σ-hole model. The unique properties of biomolecular halogen bonds (BXBs), particularly in their geometric and energetic relationship to classic hydrogen bonds, make them potentially powerful tools for inhibitor design and molecular engineering. This chapter reviews the current research on BXBs, focusing on experimental studies on their structure-energy relationships, how these studies inform the development of computational methods to model BXBs, and considers how BXBs can be applied to the rational design of more effective inhibitors against therapeutic targets and of new biological-based materials.

n-Dodecyl β-D-maltoside specifically competes with general anesthetics for anesthetic binding sites

We recently demonstrated that the anionic detergent sodium dodecyl sulfate (SDS) specifically interacts with the anesthetic binding site in horse spleen apoferritin, a soluble protein which models anesthetic binding sites in receptors. This raises the possibility of other detergents similarly interacting with and occluding such sites from anesthetics, thereby preventing the proper identification of novel anesthetic binding sites. n-Dodecyl β-D-maltoside (DDM) is a non-ionic detergent commonly used during protein-anesthetic studies because of its mild and non-denaturing properties. In this study, we demonstrate that SDS and DDM occupy anesthetic binding sites in the model proteins human serum albumin (HSA) and horse spleen apoferritin and thereby inhibit the binding of the general anesthetics propofol and isoflurane. DDM specifically interacts with HSA (Kd = 40 μM) with a lower affinity than SDS (Kd = 2 μM). DDM exerts all these effects while not perturbing the native structures of either model protein. Computational calculations corroborated the experimental results by demonstrating that the binding sites for DDM and both anesthetics on the model proteins overlapped. Collectively, our results indicate that DDM and SDS specifically interact with anesthetic binding sites and may thus prevent the identification of novel anesthetic sites. Special precaution should be taken when undertaking and interpreting results from protein-anesthetic investigations utilizing detergents like SDS and DDM.

Propofol shares the binding site with isoflurane and sevoflurane on leukocyte function-associated antigen-1

BACKGROUND

We previously demonstrated that propofol interacted with the leukocyte adhesion molecule leukocyte function-associated antigen-1 (LFA-1) and inhibited the production of interleukin-2 via LFA-1 in a dependent manner. However, the binding site(s) of propofol on LFA-1 remains unknown.

METHODS

First, the inhibition of LFA-1's ligand binding by propofol was confirmed in an enzyme-linked immunosorbent assay (ELISA) ELISA-type assay. The binding site of propofol on LFA-1 was probed with a photolabeling experiment using a photoactivatable propofol analog called azi-propofol-m. The adducted residues of LFA-1 by this compound were determined using liquid chromatography-mass spectrometry. In addition, the binding of propofol to the ligand-binding domain of LFA-1 was examined using 1-aminoanthracene (1-AMA) displacement assay. Furthermore, the binding site(s) of 1-AMA and propofol on LFA-1 was studied using the docking program GLIDE.

RESULTS

We demonstrated that propofol impaired the binding of LFA-1 to its ligand intercellular adhesion molecule-1. The photolabeling experiment demonstrated that the adducted residues were localized in the allosteric cavity of the ligand-binding domain of LFA-1 called "lovastatin site." The shift of fluorescence spectra was observed when 1-AMA was coincubated with the low-affinity conformer of LFA-1 ligand-binding domain (wild-type [WT] αL I domain), not with the high-affinity conformer, suggesting that 1-AMA bound only to WT αL I domain. In the 1-AMA displacement assay, propofol decreased 1-AMA fluorescence signal (at 520 nm), suggesting that propofol competed with 1-AMA and bound to the WT αL I domain. The docking simulation demonstrated that both 1-AMA and propofol bound to the lovastatin site, which agreed with the photolabeling experiment.

CONCLUSIONS

We demonstrated that propofol bound to the lovastatin site in LFA-1. Previously we showed that the volatile anesthetics isoflurane and sevoflurane bound to this site. Taken together, the lovastatin site is an example of the common binding sites for anesthetics currently used clinically.

Structural and functional characterization of an anesthetic binding site in the second cysteine-rich domain of protein kinase Cδ*

Elucidating the principles governing anesthetic-protein interactions requires structural determinations at high resolutions not yet achieved with ion channels. Protein kinase C (PKC) activity is modulated by general anesthetics. We solved the structure of the phorbol-binding domain (C1B) of PKCδ complexed with an ether (methoxymethylcycloprane) and with an alcohol (cyclopropylmethanol) at 1.36-Å resolution. The cyclopropane rings of both agents displace a single water molecule in a surface pocket adjacent to the phorbol-binding site, making van der Waals contacts with the backbone and/or side chains of residues Asn-237 to Ser-240. Surprisingly, two water molecules anchored in a hydrogen-bonded chain between Thr-242 and Lys-260 impart elasticity to one side of the binding pocket. The cyclopropane ring takes part in π-acceptor hydrogen bonds with the amide of Met-239. There is a crucial hydrogen bond between the oxygen atoms of the anesthetics and the hydroxyl of Tyr-236. A Tyr-236-Phe mutation results in loss of binding. Thus, both van der Waals interactions and hydrogen-bonding are essential for binding to occur. Ethanol failed to bind because it is too short to benefit from both interactions. Cyclopropylmethanol inhibited phorbol-ester-induced PKCδ activity, but failed to do so in PKCδ containing the Tyr-236-Phe mutation.

Anesthetic drug development: Novel drugs and new approaches

The ideal sedative–hypnotic drug would be a rapidly titratable intravenous agent with a high therapeutic index and minimal side effects. The current efforts to develop such agents are primarily focused on modifying the structures of existing drugs to improve their pharmacodynamic and pharmacokinetic properties. Drugs currently under development using this rational design approach include analogues of midazolam, propofol, and etomidate, such as remimazolam, PF0713, and cyclopropyl methoxycarbonyl-etomidate (MOC-etomidate), respectively. An alternative approach involves the rapid screening of large libraries of molecules for activity in structural or phenotypic assays that approximate anesthetic and target receptor interactions. Such high-throughput screening offers the potential for identifying completely novel classes of drugs. Anesthetic drug development is experiencing a resurgence of interest because there are new demands on our clinical practice that can be met, at least in part, with better agents. The goal of this review is to provide the reader with a glimpse of the novel anesthetic drugs and new developmental approaches that lie on the horizon.

Isoflurane increases neuronal cell death vulnerability by downregulating miR-214

Since accumulating evidence suggests the application of anesthetics may increase the risk of Alzheimer’s disease (AD), we investigated the cytotoxicity of inhaled general anesthesia in neurons and its underlying mechanism. Using primary cultured rat hippocampal neurons as the study model, here we show that isoflurane increases vulnerability to intracellular or extracellular amyloid β with or without serum deprivation. This isoflurane-induced effect is mediated by the downregulation of miR-214 level that lead to an elevated expression of Bax, a prominent target for miR-214. We conclude that isoflurane increases cell death in the presence of amyloid β by increasing Bax level through downregulating miR-214. Our data provide a new insight for inhaled anesthetics toxicity and indicate a possible mechanistic link between anesthetic application and neurodegenration in AD.

Halogen bonding at the ATP binding site of protein kinases: preferred geometry and topology of ligand binding

Halogenated ligands have been widely developed as potent, and frequently selective, inhibitors of protein kinases (PK). Herein, all structures of protein kinases complexed with a halogenated ligand, identified in the PDB, were analyzed in the context of eventual contribution of halogen bonding to protein-ligand interactions. Global inspection shows that two carbonyl groups of residues located in the hinge region are the most abundant halogen bond acceptors. In contrast to solution data, well-defined water molecules, located at sites conserved across most PK structures, are also involved in halogen bonding. Analysis of cumulative distributions of halogen-acceptor distances shows that structures displaying short contacts involving a halogen atom are overpopulated, contributing together to clearly defined maxima of 2.82, 2.91 and 2.94Å for chlorine, bromine and iodine, respectively. The angular preference of a halogen bond favors ideal topology (180°, 120°) for iodine. For bromine the distribution is much more dispersed, and no such preference was found for chlorine. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases (2012).

Theoretical studies of the interaction between enflurane and water

Increase of the atmospheric concentration of halogenated organic compounds is partially responsible for a change of the global climate. In this work we have investigated the interaction between halogenated ether and water, which is one of the most important constituent of the atmosphere. The structures of the complexes formed by the two most stable conformers of enflurane (a volatile anaesthetic) with one and two water molecules were calculated by means of the counterpoise CP-corrected gradient optimization at the MP2/6–311++G(d,p) level. In these complexes the CH…O_w hydrogen bonds are formed, with the H…O_w distances varying between 2.23 and 2.32 Å. A small contraction of the CH bonds and the blue shifts of the ν(CH) stretching vibrations are predicted. There is also a weak interaction between one of the F atoms and the H atom of water, with the H_w…F distances between 2.41 and 2.87 Å. The CCSD(T)/CBS calculated stabilization energies in these complexes are between −5.89 and −4.66 kcal mol⁻¹, while the enthalpies of formation are between −4.35 and −3.22 kcal mol⁻¹. The Cl halogen bonding between enflurane and water has been found in two complexes. The intermolecular (Cl···O) distance is smaller than the sum of the corresponding van der Waals radii. The CCSD(T)/CBS stabilization energies for these complexes are about −2 kcal mol⁻¹.

Figure

Synthesis and physico-chemical properties in aqueous medium of all possible isomeric bromo analogues of benzo-1H-triazole, potential inhibitors of protein kinases

In ongoing studies on the role of the individual bromine atoms of 4,5,6,7-tetrabromobenzotriazole (TBBt) in its relatively selective inhibition of protein kinase CK2α, we have prepared all the possible two mono-, four di-, and two tri-bromobenzotriazoles and determined their physicochemical properties in aqueous medium. They exhibited a general trend of a decrease in solubility with an increase in the number of bromines on the benzene ring, significantly modulated by the pattern of substitution. For a given number of attached bromines, this was directly related to the electronic effects resulting from different sites of substitution, leading to marked variations of pK(a) values for dissociation of the triazole proton. Experimental data (pK(a), solubility) and ab initio calculations demonstrated that hydration of halogenated benzotriazoles is driven by a subtle balance of hydrophobic and polar interactions. The combination of QM-derived free energies for solvation and proton dissociations was found to be a reasonably good predictor of inhibitory activity of halogenated benzotriazoles vs CK2α. Since the pattern of halogenation of the benzene ring of benzotriazole has also been shown to be one of the determinants of inhibitory potency vs some viruses and viral enzymes, the present comprehensive description of their physicochemical properties should prove helpful in efforts to elucidate reaction mechanisms, including possible halogen bonding, and the search for more selective and potent inhibitors.

General anesthetics predicted to block the GLIC pore with micromolar affinity

Although general anesthetics are known to modulate the activity of ligand-gated ion channels in the Cys-loop superfamily, there is at present neither consensus on the underlying mechanisms, nor predictive models of this modulation. Viable models need to offer quantitative assessment of the relative importance of several identified anesthetic binding sites. However, to date, precise affinity data for individual sites has been challenging to obtain by biophysical means. Here, the likely role of pore block inhibition by the general anesthetics isoflurane and propofol of the prokaryotic pentameric channel GLIC is investigated by molecular simulations. Microscopic affinities are calculated for both single and double occupancy binding of isoflurane and propofol to the GLIC pore. Computations are carried out for an open-pore conformation in which the pore is restrained to crystallographic radius, and a closed-pore conformation that results from unrestrained molecular dynamics equilibration of the structure. The GLIC pore is predicted to be blocked at the micromolar concentrations for which inhibition by isofluorane and propofol is observed experimentally. Calculated affinities suggest that pore block by propofol occurs at signifcantly lower concentrations than those for which inhibition is observed: we argue that this discrepancy may result from binding of propofol to an allosteric site recently identified by X-ray crystallography, which may cause a competing gain-of-function effect. Affinities of isoflurane and propofol to the allosteric site are also calculated, and shown to be 3 mM for isoflurane and for propofol; both anesthetics have a lower affinity for the allosteric site than for the unoccupied pore.

Although general anesthesia is performed every day on thousands of people, its detailed microscopic mechanisms are not known. What is known is that general anesthetic drugs modulate the activity of ion channels in the central nervous system. These channels are proteins that open in response to binding of neurotransmitter molecules, creating an electric current through the cell membrane and thus propagating nerve impulses between cells. One possible mechanism for ion channel inhibition by anesthetics is that the drugs bind inside the pore of the channels, blocking ion current. Here we investigate such a pore block mechanism by computing the strength of the drugs' interaction with the pore – and hence the likelihood of binding, in the case of GLIC, a bacterial channel protein. The results, obtained from numerical simulations of atomic models of GLIC, indicate that the anesthetics isoflurane and propofol have a tendency to bind in the pore that is strong enough to explain blocking of the channel, even at low concentration of the drugs.

Beyond the detergent effect: a binding site for sodium dodecyl sulfate (SDS) in mammalian apoferritin

Although sodium dodecyl sulfate (SDS) is widely used as an anionic detergent, it can also exert specific pharmacological effects that are independent of the surfactant properties of the molecule. However, structural details of how proteins recognize SDS are scarce. Here, it is demonstrated that SDS binds specifically to a naturally occurring four-helix bundle protein: horse apoferritin. The X-ray crystal structure of the apoferritin-SDS complex was determined at a resolution of 1.9 Å and revealed that the SDS binds in an internal cavity that has previously been shown to recognize various general anesthetics. A dissociation constant of 24 ± 9 µM at 293 K was determined by isothermal titration calorimetry. SDS binds in this cavity by bending its alkyl tail into a horseshoe shape; the charged SDS head group lies in the opening of the cavity at the protein surface. This crystal structure provides insights into the protein-SDS interactions that give rise to binding and may prove useful in the design of novel SDS-like ligands for some proteins.

Anesthetic mechanisms: worms light the way

In the nematode C. elegans, immobility induced by the anesthetic halothane is coupled to its ability to modulate neuronal resting membrane potential, perhaps through effects on leak channels; a similar anesthetic, isoflurane, appears to work a different way.

Structural analysis of haemin demetallation by L-chain apoferritins

There are extensive structural similarities between eukaryotic and prokaryotic ferritins. However, there is one essential difference between these two types of ferritins: bacterioferritins contain haem whereas eukaryotic ferritins are considered to be non-haem proteins. In vitro experiments had shown that horse spleen apoferritin or recombinant horse L chain apoferritins, when co-crystallised with haemin, undergoes demetallation of the porphyrin. In the present study a cofactor has been isolated directly from horse spleen apoferritin and from crystals of the mutant horse L chain apoferritin (E53Q, E56Q, E57Q, E60Q and R59M) which had been co-crystallised with haemin. In both cases the HPLC/ESI-MS results confirm that the cofactor is a N-ethylprotoporphyrin IX. Crystal structures of wild type L chain horse apoferritin and its three mutants co-crystallised with haemin have been determined to high resolution and in all cases a metal-free molecule derived from haemin was found in the hydrophobic pocket, close to the two-fold axis. The X-ray structure of the E53Q, E56Q, E57Q, E60Q+R59M recombinant horse L-chain apoferritin has been obtained at a higher resolution (1.16Å) than previously reported for any mammalian apoferritins. Similar evidence for a metal-free molecule derived from haemin was found in the electron density map of horse spleen apoferritin (at a resolution of 1.5Å). The out-of-plane distortion of the observed porphyrin is clearly compatible with an N-alkyl porphyrin. We conclude that L-chain ferritins are capable of binding and demetallating haemin, generating in the process N-ethylprotoporphyrin IX both in vivo and in vitro.

Binding site and affinity prediction of general anesthetics to protein targets using docking

BACKGROUND

The protein targets for general anesthetics remain unclear. A tool to predict anesthetic binding for potential binding targets is needed. In this study, we explored whether a computational method, AutoDock, could serve as such a tool.

METHODS

High-resolution crystal data of water-soluble proteins (cytochrome C, apoferritin, and human serum albumin), and a membrane protein (a pentameric ligand-gated ion channel from Gloeobacter violaceus [GLIC]) were used. Isothermal titration calorimetry (ITC) experiments were performed to determine anesthetic affinity in solution conditions for apoferritin. Docking calculations were performed using DockingServer with the Lamarckian genetic algorithm and the Solis and Wets local search method (http://www.dockingserver.com/web). Twenty general anesthetics were docked into apoferritin. The predicted binding constants were compared with those obtained from ITC experiments for potential correlations. In the case of apoferritin, details of the binding site and their interactions were compared with recent cocrystallization data. Docking calculations for 6 general anesthetics currently used in clinical settings (isoflurane, sevoflurane, desflurane, halothane, propofol, and etomidate) with known 50% effective concentration (EC(50)) values were also performed in all tested proteins. The binding constants derived from docking experiments were compared with known EC(50) values and octanol/water partition coefficients for the 6 general anesthetics.

RESULTS

All 20 general anesthetics docked unambiguously into the anesthetic binding site identified in the crystal structure of apoferritin. The binding constants for 20 anesthetics obtained from the docking calculations correlate significantly with those obtained from ITC experiments (P = 0.04). In the case of GLIC, the identified anesthetic binding sites in the crystal structure are among the docking predicted binding sites, but not the top ranked site. Docking calculations suggest a most probable binding site located in the extracellular domain of GLIC. The predicted affinities correlated significantly with the known EC(50) values for the 6 frequently used anesthetics in GLIC for the site identified in the experimental crystal data (P = 0.006). However, predicted affinities in apoferritin, human serum albumin, and cytochrome C did not correlate with these 6 anesthetics' known experimental EC(50) values. A weak correlation between the predicted affinities and the octanol/water partition coefficients was observed for the sites in GLIC.

CONCLUSION

We demonstrated that anesthetic binding sites and relative affinities can be predicted using docking calculations in an automatic docking server (AutoDock) for both water-soluble and membrane proteins. Correlation of predicted affinity and EC(50) for 6 frequently used general anesthetics was only observed in GLIC, a member of a protein family relevant to anesthetic mechanism.