The Ca 2+ and ADP ribose (ADPR)-activated cation channel TRPM2 is the closest homolog of the cold sensor TRPM8 but serves as a deep-brain warmth sensor. To unravel the molecular mechanism of heat sensing by the TRPM2 protein, we study here temperature dependence of TRPM2 currents in cell-free membrane patches across ranges of agonist concentrations. We find that channel gating remains strictly agonist-dependent even at 40°C: heating alone or in combination with just Ca 2+ , just ADPR, Ca 2+ + cyclic ADPR, or H 2 O 2 pretreatment only marginally activates TRPM2. For fully liganded TRPM2, pore opening is intrinsically endothermic, due to ~10-fold larger activation enthalpy for opening (~200 kJ/mol) than for closure (~20 kJ/mol). However, the temperature threshold is too high (>40°C) for unliganded but too low (<15°C) for fully liganded channels. Thus, warmth sensitivity around 37°C is restricted to narrow ranges of agonist concentrations. For ADPR, that range matches, but for Ca 2+ , it exceeds bulk cytosolic values. The supraphysiological [Ca 2+ ] needed for TRPM2 warmth sensitivity is provided by Ca 2+ entering through the channel’s pore. That positive feedback provides further strong amplification to the TRPM2 temperature response (Q 10 ~ 1,000), enabling the TRPM2 protein to autonomously respond to tiny temperature fluctuations around 37°C. These functional data together with published structures suggest a molecular mechanism for opposite temperature dependences of two closely related channel proteins.

中文翻译：

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双放大策略将 TRPM2 通道转变为超灵敏中心热探测器

钙2+和 ADP 核糖 (ADPR) 激活的阳离子通道 TRPM2 是冷传感器 TRPM8 最接近的同系物，但用作深部脑部温暖传感器。为了揭示 TRPM2 蛋白热感应的分子机制，我们在这里研究了跨激动剂浓度范围的无细胞膜片中 TRPM2 电流的温度依赖性。我们发现即使在 40°C 时，通道门控仍然严格依赖于激动剂：单独加热或仅与 Ca 组合2+, 只是 ADPR, Ca2++ 循环 ADPR，或 H2个欧2个预处理仅略微激活 TRPM2。对于完全配体的 TRPM2，孔隙打开本质上是吸热的，因为打开 (~200 kJ/mol) 的活化焓比关闭 (~20 kJ/mol) 大 10 倍。然而，温度阈值对于未配体的通道来说太高 (>40°C)，但对于完全配体的通道来说太低 (<15°C)。因此，37°C 左右的热敏感性仅限于狭窄的激动剂浓度范围。对于 ADPR，该范围匹配，但对于 Ca2+，它超过了散装细胞溶质值。超生理 [Ca2+] TRPM2 温暖敏感性所需的由 Ca 提供2+通过通道的孔隙进入。该正反馈进一步增强了 TRPM2 温度响应 (Q10~ 1,000)，使 TRPM2 蛋白能够自主响应 37°C 左右的微小温度波动。这些功能数据与已发表的结构一起表明了两种密切相关的通道蛋白的相反温度依赖性的分子机制。