Odorant receptors (ORs) in olfactory sensory neurons (OSNs) mediate detection of volatile odorants. Divalent sulfur compounds, such as thiols and thioethers, are extremely potent odorants. We identify a mouse OR, MOR244-3, robustly responding to (methylthio)methanethiol (MeSCH 2 SH; MTMT) in heterologous cells. Found specifically in male mouse urine, strong-smelling MTMT [human threshold 100 parts per billion (ppb)] is a semiochemical that attracts female mice. Nonadjacent thiol and thioether groups in MTMT suggest involvement of a chelated metal complex in MOR244-3 activation. Metal ion involvement in thiol-OR interactions was previously proposed, but whether these ions change thiol-mediated OR activation remained unknown. We show that copper ion among all metal ions tested is required for robust activation of MOR244-3 toward ppb levels of MTMT, structurally related sulfur compounds, and other metal-coordinating odorants (e.g., strong-smelling transcyclooctene) among >125 compounds tested. Copper chelator (tetraethylenepentamine, TEPA) addition abolishes the response of MOR244-3 to MTMT. Histidine 105, located in the third transmembrane domain near the extracellular side, is proposed to serve as a copper-coordinating residue mediating interaction with the MTMTcopper complex. Electrophysiological recordings of the OSNs in the septal organ, abundantly expressing MOR244-3, revealed neurons responding to MTMT. Addition of copper ion and chelator TEPA respectively enhanced and reduced the response of some MTMTresponding neurons, demonstrating the physiological relevance of copper ion in olfaction. In a behavioral context, an olfactory discrimination assay showed that mice injected with TEPA failed to discriminate MTMT. This report establishes the role of metal ions in mammalian odor detection by ORs.

Through the use of direct analysis in real time mass spectrometry (DART-MS), 2-propenesulfenic acid, an intermediate long postulated as being formed when garlic ( Allium sativum ) is crushed, has been detected for the first time and determined by mass spectrometric methods to have a half-life of <1 s at room temperature. Two other key intermediates, 2-propenesulfinic acid and diallyl trisulfane S-oxide, have also been detected for the first time in volatiles from crushed garlic, along with allicin and related thiosulfinates, allyl alcohol, sulfur dioxide, propene, and pyruvate as coproducts. A commercial dietary supplement containing garlic powder, which was sampled after crushing, was found to contain alliin, methiin, and S-allylcysteine and produced allicin upon addition of water. DART-MS detection of 1-butenesulfenic acid from the ornamental A. siculum is also reported. (Z)-Propanethial S-oxide (onion lachrymatory factor), absent in garlic, is found to be formed from crushed elephant garlic ( Allium ampeloprasum ), consistent with the classification of this plant as a closer relative of leek than of garlic. Mixtures of thiosulfinates, lachrymatory thial S-oxides, and related compounds are directly observed from crushed leek ( Allium porrum ) and Chinese chive ( Allium tuberosum ). Disulfanes and polysulfanes are detected only when the Allium samples are heated, consistent with earlier conclusions that these are not primary products from cut or crushed alliums.

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Since the discovery that RNA can catalyze chemical reactions, the number and variety of noncoding RNAs and the important roles they play in biology have been growing steadily. Backbone-modified RNA may find broad application in the fundamental biology and biomedicine of noncoding RNAs, providing that the modifications mimic the structure of the phosphodiester linkage and do not alter the conformation of RNA. In particular, the potential of RNA interference to become a new therapeutic strategy has revitalized interest in chemical modifications that may optimize the pharmacological properties of short interfering RNAs (siRNAs).[1] We are interested in hydrophobic nonionic mimics of the phosphate backbone, such as formacetals [2] and amides, [3] that may confer high nuclease resistance to siRNAs along with reduced charge and increased hydrophobicity. Earlier studies showed that 3'-CH 2 -CO-NH-5' internucleoside amide linkages (abbreviated here as AM1) were well-tolerated in the DNA strand of an A-type DNA-RNA heteroduplex.[4] Subsequently, we found that AM1 modifications did not change the thermal stability of RNA-RNA duplexes.[3] Most importantly, Iwase et al. [5] recently showed that AM1 amides were well-tolerated in the 3' overhangs of siRNAs.Taken together, these data suggest that amides may be good mimics of phosphate linkages in RNA; however, beyond simple melting-temperature measurements, the structural and thermodynamic properties of amide-modified RNA have not been established. Herein we present the first comprehensive structural and thermodynamic study that clearly shows that AM1 linkages do not disturb the A-type structure, thermal stability, and hydration of RNA duplexes. Despite the different geometry, amide AM1 appears to be an excellent mimic of the phosphate linkage in RNA. Our study complements structural studies on amide-modified DNA [4,6] and provides the first detailed insight into how the AM1 amide is accommodated in an RNA duplex.We started by designing a new route for the synthesis of the r(U AM1 A) dimer phosphoramidite, which was used to prepare the amide-modified RNA sequences (Scheme 1). The tert-butyldimethylsilyl (TBS) groups in the known 3'-allyluridine 1 [3] were replaced with 5'-O-methoxytrityl (MMT) and 2'-O-acetyl protecting groups suitable for solid-phase RNA synthesis. Two-step oxidative degradation of the alkene gave the carboxylic acid part 6 of the r(U AM1 A) dimer. [4a,b] For the synthesis of the amine part, we designed a novel route involving selective protection of the 2'-OH group of 5'-aminoadenosine with the triisopropylsilyloxymethyl (TOM) group. Treatment of 5'-azido-N-benzoyladenosine (7) with dibutyltin chloride followed by TOM chloride gave a mixture of 2'-and 3'-O-TOM nucleosides, from which the desired compound 8 was isolated in 30 % yield. Reduction of the azide gave the amine 9, which was coupled with the carboxylic acid 6 to give the dimer 10 (Scheme 2). Although protection of the 2'-OH group of adenosine 7 was relatively low-yielding, this strategy was advant...