Department of Pathophysiology, Key Laboratory of Cell Differentiation and Apoptosis of National Ministry of Education, Shanghai E-Institute for Chemical Biology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.
Proc Natl Acad Sci U S A. 2012 Feb 28;109(9):3492-7. doi: 10.1073/pnas.1111297109. Epub 2012 Feb 10.
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 trans-cyclooctene) 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 MTMT-copper 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 MTMT-responding 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.
气味受体（ORs）在嗅觉感觉神经元（OSNs）中介导挥发性气味物质的检测。二价硫化合物，如硫醇和硫醚，是非常有效的气味物质。我们鉴定出一种老鼠 OR，MOR244-3，在异源细胞中对（甲基硫代）甲硫醇（MeSCH(2)SH；MTMT）有强烈的反应。MTMT 强烈的气味仅存在于雄性老鼠的尿液中，是一种半化学物质，吸引雌性老鼠。MTMT 中非相邻的硫醇和硫醚基团表明，它可能参与了 MOR244-3 的激活。金属离子在硫醇-OR 相互作用中的参与先前已被提出，但这些离子是否改变了硫醇介导的 OR 激活仍不清楚。我们表明，在所测试的所有金属离子中，铜离子是 MOR244-3 对 MTMT、结构相关的硫化合物以及其他金属配位气味物质（例如，强烈气味的反式环辛烯）在 ppb 水平下的强烈激活所必需的，在 >125 种测试化合物中。铜螯合剂（四乙五胺，TEPA）的添加会消除 MOR244-3 对 MTMT 的反应。位于第三跨膜域靠近细胞外侧的组氨酸 105 被提议作为铜配位残基，介导与 MTMT-铜复合物的相互作用。在富含表达 MOR244-3 的隔区器官中的 OSN 的电生理记录显示，神经元对 MTMT 有反应。铜离子和螯合剂 TEPA 的添加分别增强和减少了一些对 MTMT 有反应的神经元的反应，证明了铜离子在嗅觉中的生理相关性。在行为学背景下，嗅觉辨别试验表明，注射 TEPA 的老鼠无法辨别 MTMT。本报告确立了金属离子在哺乳动物气味检测中的作用。
