Department of Biomedical Sciences, Cornell University, Ithaca, New York 14853, USA.
J Biol Chem. 2010 Apr 9;285(15):11547-56. doi: 10.1074/jbc.M109.058727. Epub 2010 Feb 9.
The capsaicin receptor (TRPV1) is a nonselective cation channel that integrates multiple painful stimuli, including capsaicin, protons, and heat. Protons facilitate the capsaicin- and heat-induced currents by decreasing thermal threshold or increasing agonist potency for TRPV1 activation (Tominaga, M., Caterina, M. J., Malmberg, A. B., Rosen, T. A., Gilbert, H., Skinner, K., Raumann, B. E., Basbaum, A. I., and Julius, D. (1998) Neuron 21, 531-543). In the presence of saturating capsaicin, rat TRPV1 (rTRPV1) reaches full activation, with no further stimulation by protons. Human TRPV1 (hTRPV1), a species ortholog with high homology to rTRPV1, is potentiated by extracellular protons and magnesium, even at saturating capsaicin. We investigated the structural basis for protons and magnesium modulation of fully capsaicin-bound human receptors. By analysis of chimeric channels between hTRPV1 and rTRPV1, we found that transmembrane domain 1-4 (TM1-4) of TRPV1 determines whether protons can further open the fully capsaicin-bound receptors. Mutational analysis identified a titratable glutamate residue (Glu-536) in the linker between TM3 and TM4 critical for further stimulation of fully liganded hTRPV1. In contrast, hTRPV1 TM5-6 is required for magnesium augmentation of capsaicin efficacy. Our results demonstrate that capsaicin efficacy of hTRPV1 correlates with the extracellular ion milieu and unravel the relevant structural basis of modulation by protons and magnesium.
辣椒素受体 (TRPV1) 是一种非选择性阳离子通道，可整合多种疼痛刺激物，包括辣椒素、质子和热。质子通过降低热阈值或增加 TRPV1 激活的激动剂效力来促进辣椒素和热诱导的电流 (Tominaga, M., Caterina, M. J., Malmberg, A. B., Rosen, T. A., Gilbert, H., Skinner, K., Raumann, B. E., Basbaum, A. I., and Julius, D. (1998) Neuron 21, 531-543)。在存在饱和辣椒素的情况下，大鼠 TRPV1(rTRPV1) 达到完全激活，质子不再进一步刺激。与人 TRPV1(hTRPV1) 具有高度同源性的种系同源物，即使在饱和辣椒素存在下，也被细胞外质子和镁增强。我们研究了质子和镁调节完全结合辣椒素的人受体的结构基础。通过分析 hTRPV1 和 rTRPV1 之间的嵌合体通道，我们发现 TRPV1 的跨膜域 1-4 (TM1-4) 决定了质子是否可以进一步打开完全结合辣椒素的受体。突变分析确定了 TM3 和 TM4 之间连接体中一个可滴定的谷氨酸残基 (Glu-536) 对于完全结合的 hTRPV1 的进一步刺激至关重要。相比之下，hTRPV1 的 TM5-6 对于镁增强辣椒素效力是必需的。我们的结果表明，hTRPV1 的辣椒素效力与细胞外离子环境相关，并揭示了质子和镁调节的相关结构基础。
