Effects of Strigolactones on NLRP3 Activation, Nitrosative Stress, and Antioxidant Mox Phenotype: In Vitro and In Silico Evidence.

Phytohormones have significant roles in redox metabolism, inflammatory responses, and cellular survival mechanisms within the microenvironment of the mammalian brain. Herein, we identified the mammalian molecular targets of three representative strigolactone (SL) analogues structurally derived from apocarotenoids and the functional equivalent of plant hormones. All tested SL analogues have an inhibitory effect on NLRP3 inflammasome-mediated IL-1ß release in murine microglial cells. However, IND and EGO10 became prominent among them due to their high potency at low micromolar doses. All SL analogues dose-dependently suppressed the release and expression of proinflammatory factors. For EGO10 and IND, IC50 values for iNOS-associated NO secretion were as low as 1.72 and 1.02 µM, respectively. In silico analyses revealed that (S)-EGO10 interacted with iNOS, NLRP3, and Keap1 ligands with the highest binding affinities among all stereoisomeric SL analogues. Although all compounds were effective in microglial Mox phenotype polarization, 4-Br-debranone exhibited a differential pattern for upregulating Nrf2-driven downstream enzymes.

1H-Indole-2,3-dione 3-thiosemicarbazones carrying a 4-sulfamoylphenyl moiety with selective antiviral activity against reovirus-1.

1H-indole-2,3-dione 3-[4-(4-sulfamoylphenyl)thiosemicarbazones] (6a-j) were evaluated against Para-influenza-3, Reovirus-1, Sindbis, Coxsackie B4 and Punto Toro viruses. New 1-methyl-1H-indole-2,3-dione 3-[4-(4-sulfamoylphenyl)thiosemicarbazones] (7a-c) were synthesized to evaluate the contribution of methyl substitution at position 1- of the indole ring to antiviral activity. The test results showed that compounds 5-trifluoromethoxy- substituted 6c (EC50: 2-9 µM) and 5-bromo- substituted 6f (EC50: 2-3 µM) have non-toxic selective antiviral activity while not all standards are active against Reovirus-1. Molecular docking studies of 6c and 6f were carried out to determine the possible binding positions with Reovirus-1. Trifluoromethoxy and bromine substitutions at position 5- of the indole ring provided selective antiviral activity, while methyl substitution at position 1- of the indole ring significantly decreased the activity and increased toxicity against Reovirus-1.

Evaluation of Bacteriophage ϕ11 host recognition protein and its host-binding peptides for diagnosing/targeting of Saphylococcus aureus infections.

Evaluating the potential of using both synthetic and biological products as targeting agents for the diagnosis, imaging, and treatment of infections due to particularly antibiotic-resistant pathogens is important for controlling infections. We examined the interaction between Gp45, a receptor-binding protein of the ϕ11 lysogenic phage, and its host S. aureus, a common cause of nosocomial infections. Using molecular dynamics and docking simulations, we identified the peptides that bind to S. aureus wall teichoic acids via Gp45. We compared the binding affinity of Gp45 and the two highest-scoring peptide sequences (P1 and P3) and their scrambled forms using microscopy, spectroscopy, and ELISA. Our results revealed that rGp45 (recombinant Gp45) and chemically synthesized P1 had a higher binding affinity for S. aureus compared with all other peptides, with the exception of E. coli. Furthermore, rGp45 had a capture efficiency of over 86%; P1 had a capture efficiency of over 64%. Overall, our findings suggest that receptor-binding proteins such as rGp45, which provide a critical initiation of the phage life cycle for host adsorption, might play an important role in the diagnosis, imaging, and targeting of bacterial infections. Studying such proteins could accordingly enable the development of effective strategies for controlling infections.

Exome data of developmental and epileptic encephalopathy patients reveals de novo and inherited pathologic variants in epilepsy-associated genes.

PURPOSE: In Developmental and Epileptic Encephalopathies (DEEs), identifying the precise genetic factors guides the clinicians to apply the most appropriate treatment for the patient. Due to high locus heterogeneity, WES analysis is a promising approach for the genetic diagnosis of DEE. Therefore, the aim of the present study is to evaluate the utility of WES in the diagnosis and treatment of DEE patients. METHODS: The exome data of 29 DEE patients were filtrated for destructive and missense mutations in 1896 epilepsy-related genes to detect the causative variants and examine the genotype-phenotype correlations. We performed Sanger sequencing with the available DNA samples to follow the co-segregation of the variants with the disease phenotype in the families. Also, the structural effects of p.Asn1053Ser, p.Pro120Ser and p.Glu1868Gly mutations on KCNMA1, NPC2, and SCN2A proteins, respectively, were evaluated by molecular dynamics (MD) and molecular docking simulations. RESULTS: Out of 29, nine patients (31%) harbor pathological (P) or likely pathological (LP) mutations in SCN2A, KCNQ2, ATP1A2, KCNMA1, and MECP2 genes, and three patients have VUS variants (10%) in SCN1A and SCN2A genes. Sanger sequencing results indicated that three of the patients have de novo mutations while eight of them carry paternally and/or maternally inherited causative variants. MD and molecular docking simulations supported the destructive effects of the mutations on KCNMA1, NPC2, and SCN2A protein structures. CONCLUSION: Herein we demonstrated the effectiveness of WES for DEE with high locus heterogeneity. Identification of the genetic etiology guided the clinicians to adjust the proper treatment for the patients.

Strigolactone Analogs: Two New Potential Bioactiphores for Glioblastoma.

Strigolactones (SLs), carotenoid-derived phytohormones, control the plant response and signaling pathways for stressful conditions. In addition, they impact numerous cellular processes in mammalians and present new scaffolds for various biomedical applications. Recent studies demonstrated that SLs possess potent antitumor activity against several cancer cells. Herein, we sought to elucidate the inhibitory effects of SL analogs on the growth and survival of human brain tumor cell lines. Among four tested SLs, we showed for the first time that two lead bioactiphores, indanone-derived SL and EGO10, can inhibit cancer cell proliferation, induce apoptosis, and induce G1 cell cycle arrest at low concentrations. SL analogs were marked by increased expression of Bax/Caspase-3 genes and downregulation of Bcl-2. In silico studies were conducted to identify drug-likeness, blood-brain barrier penetrating properties, and molecular docking with Bcl-2 protein. Taken together, this study indicates that SLs may be promising antiglioma agents, presenting novel pharmacophores for further preclinical and clinical assessment.

Structural rearrangement of Neisseria meningitidis transferrin binding protein A (TbpA) prior to human transferrin protein (hTf) binding.

Gram-negative bacterium Neisseria meningitidis, responsible for human infectious disease meningitis, acquires the iron (Fe3+) ion needed for its survival from human transferrin protein (hTf). For this transport, transferrin binding proteins TbpA and TbpB are facilitated by the bacterium. The transfer cannot occur without TbpA, while the absence of TbpB only slows down the transfer. Thus, understanding the TbpA-hTf binding at the atomic level is crucial for the fight against bacterial meningitis infections. In this study, atomistic level of mechanism for TbpA-hTf binding is elucidated through 100 ns long all-atom classical MD simulations on free (uncomplexed) TbpA. TbpA protein underwent conformational change from 'open' state to 'closed' state, where two loop domains, loops 5 and 8, were very close to each other. This state clearly cannot accommodate hTf in the cleft between these two loops. Moreover, the helix finger domain, which might play a critical role in Fe3+ ion uptake, also shifted downwards leading to unfavorable Tbp-hTf binding. Results of this study indicated that TbpA must switch between 'closed' state to 'open' state, where loops 5 and 8 are far from each other creating a cleft for hTf binding. The atomistic level of understanding to conformational switch is crucial for TbpA-hTf complex inhibition strategies. Drug candidates can be designed to prevent this conformational switch, keeping TbpA locked in 'closed' state.

Computational analysis of functional monomers used in molecular imprinting for promising COVID-19 detection.

Today, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has recently caused a severe outbreak worldwide. There are still several challenges in COVID-19 diagnoses, such as limited reagents, equipment, and long turnaround times. In this research, we propose to design molecularly imprinted polymers as a novel approach for the rapid and accurate detection of SARS-CoV-2. For this purpose, we investigated molecular interactions between the target spike protein, receptor-binding domain of the virus, and the common functional monomers used in molecular imprinting by a plethora of computational analyses; sequence analysis, molecular docking, and molecular dynamics (MD) simulations. Our results demonstrated that AMPS and IA monomers gave promising results on the SARS-CoV-2 specific TEIYQAGST sequence for further analysis. Therefore, we propose an epitope approach-based synthesis route for specific recognition of SARS-CoV-2 by using AMPS and IA as functional monomers and the peptide fragment of the TEIYQAGST sequence as a template molecule.

Comparison of clinically approved molecules on SARS-CoV-2 drug target proteins: a molecular docking study.

The new type of coronavirus, SARS-CoV-2 has affected more than 22.6 million people worldwide. Since the first day the virus was spotted in Wuhan, China, numerous drug design studies have been conducted all over the globe. Most of these studies target the receptor-binding domain of spike protein of SARS-CoV-2, which is known to bind to the human ACE2 receptor and SARS-CoV-2 main protease, vital for the virus' replication. However, there might be a third target, human furin protease, which cleaves the virus' S1-S2 domains playing an active role in its entry into the host cell. In this study, we docked five clinically used drug molecules, favipiravir, hydroxychloroquine, remdesivir, lopinavir, and ritonavir onto three target proteins, the receptor-binding domain of SARS-CoV-2 spike protein, SARS-CoV-2 main protease, and human furin protease. Results of molecular docking simulations revealed that human furin protease might be targeted by COVID-19. Remdesivir, a nucleic acid derivative, strongly bound to the active site of this protease, suggesting that this molecule can be used as a template for designing novel furin protease inhibitors to fight against the disease. Protein-drug interactions revealed in this study at the molecular level, can pave the way for better drug design for each specific target.

HNF1A-MODY Mutations in Nuclear Localization Signal Impair HNF1A-Import Receptor KPNA6 Interactions.

Mutations in hepatocyte nuclear factor (HNF)1A gene cause the most common form of Maturity-onset diabetes of the young (MODY), a monogenic subtype of diabetes mellitus. Functional characterization of mutant proteins reveals that mutations may disrupt DNA binding capacity, transactivation ability and nuclear localization of HNF1A depending on the position of the mutation. Previously identified Arg271Trp and Ser345Tyr mutations in HNF1A were found to be defective in nuclear localization. Arg271 residue resides in a region similar to classical nuclear localization signal (NLS) motif, while Ser345 does not. Importin α family members recognize NLS motifs on cargo proteins and subsequently translocate them into nucleus. Here, we first investigated the nuclear localization mechanism of wild type HNF1A protein. For this purpose, we analyzed the interaction of HNF1A with three mouse homolog importin α proteins (KPNA2, KPNA4 and KPNA6) by co-immunoprecipitation assay and molecular docking simulation. Hereby, KPNA6 was identified as the main import receptor, which is responsible for the transport of HNF1A into the nucleus. Immunolocalization studies in mouse pancreatic cells (Min6) also confirmed the co-localization of HNF1A and KPNA6 in the cytoplasm. Secondly, the interaction between KPNA6 and mutant HNF1A proteins (Arg271Trp and Ser345Tyr) was assessed. Co-immunoprecipitation studies revealed a reduced interaction compared to wild type HNF1A. Our study demonstrated for the first time that HNF1A transcription factor is recognized and transported by importin/karyopherin import family, and mutations in NLS motifs may disrupt the interaction leading to nuclear localization abnormalities and MODY phenotype.

Synthesis, in vitro cytotoxic and apoptotic effects, and molecular docking study of novel adamantane derivatives.

[4-(Adamantane-1-carboxamido)-3-oxo-1-thia-4-azaspiro[4.4]nonan-2-yl]acetic acid (4a) and [4-(adamantane-1-carboxamido)-8-nonsubstituted/substituted-3-oxo-1-thia-4-azas-piro[4.5]decane-2-yl]acetic acid (4b-g) derivatives were synthesized; their structures were verified by elemental analysis, infrared spectroscopy, 1 H nuclear magnetic resonance (NMR), 13 C NMR, and mass spectroscopy data; and their in vitro cytotoxicity activities were investigated against human hepatocellular carcinoma, human prostate adenocarcinoma, and human lung carcinoma cell lines (HepG2, PC-3, and A549, respectively), and a mouse fibroblast cell line (NIH/3T3). All compounds, except compound 4e, were found as cytotoxic, especially on A549 cells as compared with the other cells (selectivity index = 2.01-11.6). As a further step, the effects of compounds 4a-c on apoptosis induction were tested and the expression of selected apoptosis genes was analyzed. Among the selected compounds, compound 4a induced apoptosis remarkably. Moreover, computational calculations of the binding of compounds 4a-c to the BIR3 domain of the human inhibitor of apoptosis protein revealed ligand-protein interactions at the atomistic level and emphasized the importance of a hydrophobic moiety on the ligands for better binding.

Synthesis, molecular modeling and antiviral activity of novel 5-fluoro-1H-indole-2,3-dione 3-thiosemicarbazones.

In this work, novel 5-fluoro-1-methyl/ethyl-1H-indole-2,3-dione 3-[4-(substituted phenyl)-thiosemicarbazones] 6a-n and 7a-n were synthesized. The antiviral effects of the compounds were tested against HSV-1 (KOS), HSV-2 (G) HSV-1 TK- KOS ACVr and VV in HEL cell cultures using acyclovir and ganciclovir as standards, and Coxsackie B4 virus in Vero cell cultures using ribavirin and mycophenolic acid as standards. R2 ethyl substituted 7 derivatives were found effective against viruses tested. R1 4-CF3 substituted 7d, R1 4-OCH3 substituted 7 g and R1 3-Cl substituted 7 l showed activity against HSV-1 (KOS), HSV-2 (G) HSV-1 TK- KOS ACVr and VV. Whereas only R1 4-Br substituted 7n has selective activity against coxsackie B4 virus. Molecular modelingstudies of 7d and 7l were performed to determine binding side on HSV-1 glycoprotein B and D, HSV-2 glycoprotein B structures.

Novel N-(1-thia-4-azaspiro[4.5]decan-4-yl)carboxamide derivatives as potent and selective influenza virus fusion inhibitors.

Hemagglutinin is the surface protein of the influenza virus that mediates both binding and penetration of the virus into host cells. We here report on the synthesis and structure-activity relationship of some novel N-(1-thia-4-azaspiro[4.5]decan-4-yl)-carboxamide compounds carrying the 5-chloro-2-methoxybenzamide structure, designed as influenza virus fusion inhibitors. The carboxamides (1a-h, 2a-h) have a similar backbone structure as the fusion inhibitors that we reported on previously. Compounds 2b and 2d displayed inhibitory activity against influenza A/H3N2 virus replication (average antiviral EC50 : 2.1 µM for 2b and 3.4 µM for 2d). Data obtained in the hemolysis inhibition assay supported that these compounds act as inhibitors of the influenza virus hemagglutinin-mediated fusion process.

Computational insight into the phthalocyanine-DNA binding via docking and molecular dynamics simulations.

Phthalocyanines are considered as good DNA binders, which makes them promising anti-tumor drug leads. The purpose of this study is to investigate the interactions between DNA and quaternary metallophthalocyanine derivatives (Q-MPc) possessing varying metals (M = Zn, Ni, Cu, Fe, Mg and Ca) by molecular docking since there seems to be a lack of information in the literature regarding this issue. In this direction, Autodock Vina and Molegro Virtual Docker programs were employed. Autodock Vina results reveal that each Q-MPc derivative binds to DNA strongly with similar binding energies and almost identical binding modes. They bind to the grooves of DNA by constituting favorable interactions between phosphate groups of DNA and Q-MPcs. Although changing the metal has no significant effect on binding, presence of quaternary amine substituents increases the binding constant Kb by about 2-fold comparing to the core Pc (ZnPc). Contrary to Autodock Vina, the calculated Molegro Virtual Docker binding scores have been more diverse indicating that the scoring function of Molegro is better in differentiating these metals. Despite the fact that Molegro is superior to Autodock Vina in terms of metal characterization, Autodock Vina and Molegro exhibit similar binding sites for the studied metallophthalocyanines. We propose that Q-MPc derivatives designed in this study are promising anti-tumor lead compounds since they tightly bind to DNA with considerably high Kb values. Cationic substituents and presence of metal have both positive effects on DNA binding which is critical for designing DNA-active drugs. Additional calculations employing molecular dynamics (MD) simulations verified the stability of Q-MPc-DNA complexes which remained in contact after 20 ns via attractive interactions mainly between DNA backbone and the Pc metal center.

Molecular mechanism of activation of human musk receptors OR5AN1 and OR1A1 by (R)-muscone and diverse other musk-smelling compounds.

Understanding olfaction at the molecular level is challenging due to the lack of crystallographic models of odorant receptors (ORs). To better understand the molecular mechanism of OR activation, we focused on chiral (R)-muscone and other musk-smelling odorants due to their great importance and widespread use in perfumery and traditional medicine, as well as environmental concerns associated with bioaccumulation of musks with estrogenic/antiestrogenic properties. We experimentally and computationally examined the activation of human receptors OR5AN1 and OR1A1, recently identified as specifically responding to musk compounds. OR5AN1 responds at nanomolar concentrations to musk ketone and robustly to macrocyclic sulfoxides and fluorine-substituted macrocyclic ketones; OR1A1 responds only to nitromusks. Structural models of OR5AN1 and OR1A1 based on quantum mechanics/molecular mechanics (QM/MM) hybrid methods were validated through direct comparisons with activation profiles from site-directed mutagenesis experiments and analysis of binding energies for 35 musk-related odorants. The experimentally found chiral selectivity of OR5AN1 to (R)- over (S)-muscone was also computationally confirmed for muscone and fluorinated (R)-muscone analogs. Structural models show that OR5AN1, highly responsive to nitromusks over macrocyclic musks, stabilizes odorants by hydrogen bonding to Tyr260 of transmembrane α-helix 6 and hydrophobic interactions with surrounding aromatic residues Phe105, Phe194, and Phe207. The binding of OR1A1 to nitromusks is stabilized by hydrogen bonding to Tyr258 along with hydrophobic interactions with surrounding aromatic residues Tyr251 and Phe206. Hydrophobic/nonpolar and hydrogen bonding interactions contribute, respectively, 77% and 13% to the odorant binding affinities, as shown by an atom-based quantitative structure-activity relationship model.

Structural and Mechanistic Insights into Development of Chemical Tools to Control Individual and Inter-Related Pathological Features in Alzheimer's Disease.

To elucidate the involvement of individual and inter-related pathological factors [i.e., amyloid-ß (Aß), metals, and oxidative stress] in the pathogenesis of Alzheimer's disease (AD), chemical tools have been developed. Characteristics required for such tool construction, however, have not been clearly identified; thus, the optimization of available tools or new design has been limited. Here, key structural properties and mechanisms that can determine tools' regulatory reactivities with multiple pathogenic features found in AD are reported. A series of small molecules was built up through rational structural selection and variations onto the framework of a tool useful for in vitro and in vivo metal-Aß investigation. Variations include: (i) location and number of an Aß interacting moiety; (ii) metal binding site; and (iii) denticity and structural flexibility. Detailed biochemical, biophysical, and computational studies were able to provide a foundation of how to originate molecular formulas to devise chemical tools capable of controlling the reactivities of various pathological components through distinct mechanisms. Overall, this multidisciplinary investigation illustrates a structure-mechanism-based strategy of tool invention for such a complicated brain disease.

Functional characterisation of the type 1 von Willebrand disease candidate VWF gene variants: p.M771I, p.L881R and p.P1413L.

BACKGROUND: Abnormalities in the biosynthetic pathway or increased clearance of plasma von Willebrand factor (VWF) are likely to contribute to decreased plasma VWF levels in inherited type 1 von Willebrand disease (VWD). Recent studies demonstrated that 65% of type 1 VWD patients have candidate VWF mutations, the majority of which are missense variants. The purpose of this study was to explore the effects of three VWF missense mutations (p.M771I, p.L881R and p.P1413L) located in different functional domains of VWF, reported as candidate mutations in type 1 VWD patients in the course of the MCMDM-1VWD study. MATERIALS AND METHODS: The focus of these studies was on the intracellular biosynthetic processing and localisation of VWF in a heterologous cell system. Molecular dynamic simulation for p.M771I and p.P1413L was also performed to analyse the conformational effects of the changes. RESULTS: As determined by immunofluorescence antibody staining and confocal microscopy of HEK293 cells, the intracellular localisation of recombinant VWF with the p.M771I variation was impaired. Transient transfection studies and phorbol myristate acetate stimulation in COS-7 cells revealed significant intracellular retention. In addition, major loss of VWF multimers was observed for only the p.M771I mutation. Molecular dynamic simulations on p.M771I mutant VWF revealed distinct structural rearrangements including a large deviation in the E' domain, and significant loss of ß-sheet secondary structure. DISCUSSION: The pathogenic effects of candidate VWF gene mutations were explored in this study. In vitro expression studies in heterologous cell systems revealed impaired secretion of VWF and a dominant negative effect on the processing of the wild-type protein for only the p.M771I mutation and none of the mutations affected the regulated secretion.

Mechanisms of peptide hydrolysis by aspartyl and metalloproteases.

Peptide hydrolysis has been involved in a wide range of biological, biotechnological, and industrial applications. In this perspective, the mechanisms of three distinct peptide bond cleaving enzymes, beta secretase (BACE1), insulin degrading enzyme (IDE), and bovine lens leucine aminopeptidase (BILAP), have been discussed. BACE1 is a catalytic Asp dyad [Asp, Asp-] containing aspartyl protease, while IDE and BILAP are mononuclear [Zn(His, His, Glu)] and binuclear [Zn1(Asp, Glu, Asp)-Zn2(Lys, Glu, Asp, Asp)] core possessing metallopeptidases, respectively. Specifically, enzyme-substrate interactions and the roles of metal ion(s), the ligand environment, second coordination shell residues, and the protein environment in the functioning of these enzymes have been elucidated. This information will be useful to design small inhibitors, activators, and synthetic analogues of these enzymes for biomedical, biotechnological, and industrial applications.

A Redox-Active, Compact Molecule for Cross-Linking Amyloidogenic Peptides into Nontoxic, Off-Pathway Aggregates: In Vitro and In Vivo Efficacy and Molecular Mechanisms.

Chemical reagents targeting and controlling amyloidogenic peptides have received much attention for helping identify their roles in the pathogenesis of protein-misfolding disorders. Herein, we report a novel strategy for redirecting amyloidogenic peptides into nontoxic, off-pathway aggregates, which utilizes redox properties of a small molecule (DMPD, N,N-dimethyl-p-phenylenediamine) to trigger covalent adduct formation with the peptide. In addition, for the first time, biochemical, biophysical, and molecular dynamics simulation studies have been performed to demonstrate a mechanistic understanding for such an interaction between a small molecule (DMPD) and amyloid-ß (Aß) and its subsequent anti-amyloidogenic activity, which, upon its transformation, generates ligand-peptide adducts via primary amine-dependent intramolecular cross-linking correlated with structural compaction. Furthermore, in vivo efficacy of DMPD toward amyloid pathology and cognitive impairment was evaluated employing 5xFAD mice of Alzheimer's disease (AD). Such a small molecule (DMPD) is indicated to noticeably reduce the overall cerebral amyloid load of soluble Aß forms and amyloid deposits as well as significantly improve cognitive defects in the AD mouse model. Overall, our in vitro and in vivo studies of DMPD toward Aß with the first molecular-level mechanistic investigations present the feasibility of developing new, innovative approaches that employ redox-active compounds without the structural complexity as next-generation chemical tools for amyloid management.

An Extended Polyanion Activation Surface in Insulin Degrading Enzyme.

Insulin degrading enzyme (IDE) is believed to be the major enzyme that metabolizes insulin and has been implicated in the degradation of a number of other bioactive peptides, including amyloid beta peptide (Aß), glucagon, amylin, and atrial natriuretic peptide. IDE is activated toward some substrates by both peptides and polyanions/anions, possibly representing an important control mechanism and a potential therapeutic target. A binding site for the polyanion ATP has previously been defined crystallographically, but mutagenesis studies suggest that other polyanion binding modes likely exist on the same extended surface that forms one wall of the substrate-binding chamber. Here we use a computational approach to define three potential ATP binding sites and mutagenesis and kinetic studies to confirm the relevance of these sites. Mutations were made at four positively charged residues (Arg 429, Arg 431, Arg 847, Lys 898) within the polyanion-binding region, converting them to polar or hydrophobic residues. We find that mutations in all three ATP binding sites strongly decrease the degree of activation by ATP and can lower basal activity and cooperativity. Computational analysis suggests conformational changes that result from polyanion binding as well as from mutating residues involved in polyanion binding. These findings indicate the presence of multiple polyanion binding modes and suggest the anion-binding surface plays an important conformational role in controlling IDE activity.

Implausibility of the vibrational theory of olfaction.

The vibrational theory of olfaction assumes that electron transfer occurs across odorants at the active sites of odorant receptors (ORs), serving as a sensitive measure of odorant vibrational frequencies, ultimately leading to olfactory perception. A previous study reported that human subjects differentiated hydrogen/deuterium isotopomers (isomers with isotopic atoms) of the musk compound cyclopentadecanone as evidence supporting the theory. Here, we find no evidence for such differentiation at the molecular level. In fact, we find that the human musk-recognizing receptor, OR5AN1, identified using a heterologous OR expression system and robustly responding to cyclopentadecanone and muscone, fails to distinguish isotopomers of these compounds in vitro. Furthermore, the mouse (methylthio)methanethiol-recognizing receptor, MOR244-3, as well as other selected human and mouse ORs, responded similarly to normal, deuterated, and (13)C isotopomers of their respective ligands, paralleling our results with the musk receptor OR5AN1. These findings suggest that the proposed vibration theory does not apply to the human musk receptor OR5AN1, mouse thiol receptor MOR244-3, or other ORs examined. Also, contrary to the vibration theory predictions, muscone-d30 lacks the 1,380- to 1,550-cm(-1) IR bands claimed to be essential for musk odor. Furthermore, our theoretical analysis shows that the proposed electron transfer mechanism of the vibrational frequencies of odorants could be easily suppressed by quantum effects of nonodorant molecular vibrational modes. These and other concerns about electron transfer at ORs, together with our extensive experimental data, argue against the plausibility of the vibration theory.