Mutation of a conserved glutamine residue does not abolish desensitization of acid-sensing ion channel 1.

Rook et al. assess how mutations in acid-sensing ion channel 1 (ASIC1) affect channel desensitization. They establish that, contrary to previous reports, a glutamine to glycine substitution does not abolish desensitization, but causes complex pH-dependent effects on channel desensitization. Desensitization is a common feature of ligand-gated ion channels, although the molecular cause varies widely between channel types. Mutations that greatly reduce or nearly abolish desensitization have been described for many ligand-gated ion channels, including glutamate, GABA, glycine, and nicotinic receptors, but not for acid-sensing ion channels (ASICs) until recently. Mutating Gln276 to a glycine (Q276G) in human ASIC1a was reported to mostly abolish desensitization at both the macroscopic and the single channel levels, potentially providing a valuable tool for subsequent studies. However, we find that in both human and chicken ASIC1, the effect of Q276G is modest. In chicken ASIC1, the equivalent Q277G slightly reduces desensitization when using pH 6.5 as a stimulus but desensitizes, essentially like wild-type, when using more acidic pH values. In addition, steady-state desensitization is intact, albeit right-shifted, and recovery from desensitization is accelerated. Molecular dynamics simulations indicate that the Gln277 side chain participates in a hydrogen bond network that might stabilize the desensitized conformation. Consistent with this, destabilizing this network with the Q277N or Q277L mutations largely mimics the Q277G phenotype. In human ASIC1a, the Q276G mutation also reduces desensitization, but not to the extent reported previously. Interestingly, the kinetic consequences of Q276G depend on the human variant used. In the common G212 variant, Q276G slows desensitization, while in the rare D212 variant desensitization accelerates. Our data reveal that while the Q/G mutation does not abolish or substantially impair desensitization as previously reported, it does point to unexpected differences between chicken and human ASICs and the need for careful scrutiny before using this mutation in future studies.

鲁克等人评估了酸敏感离子通道1（ASIC1）的突变如何影响通道的脱敏作用。他们证实，与先前的报道相反，谷氨酰胺到甘氨酸的替换不会消除脱敏作用，而是会对通道脱敏产生复杂的依赖于pH的影响。 脱敏是配体门控离子通道的一个常见特征，尽管不同通道类型之间其分子原因差异很大。许多配体门控离子通道都有能极大降低或几乎消除脱敏作用的突变被描述，包括谷氨酸、γ - 氨基丁酸、甘氨酸和烟碱受体，但直到最近酸敏感离子通道（ASICs）还没有。据报道，在人ASIC1a中将谷氨酰胺276突变为甘氨酸（Q276G）在宏观和单通道水平上大多会消除脱敏作用，这可能为后续研究提供一个有价值的工具。然而，我们发现，在人和鸡的ASIC1中，Q276G的影响都不大。在鸡ASIC1中，当使用pH 6.5作为刺激时，等效的Q277G会略微降低脱敏作用，但当使用更酸性的pH值时，其脱敏情况基本与野生型相同。此外，稳态脱敏作用是完整的，尽管会右移，而且从脱敏状态的恢复会加快。分子动力学模拟表明，谷氨酰胺277侧链参与一个氢键网络，该网络可能稳定脱敏构象。与此一致的是，用Q277N或Q277L突变破坏这个网络在很大程度上模拟了Q277G的表型。在人ASIC1a中，Q276G突变也会降低脱敏作用，但没有达到先前报道的程度。有趣的是，Q276G的动力学结果取决于所使用的人源变体。在常见的G212变体中，Q276G会减缓脱敏作用，而在罕见的D212变体中脱敏作用会加快。我们的数据表明，虽然Q/G突变并不像先前报道的那样消除或大幅损害脱敏作用，但它确实指出了鸡和人ASIC之间意想不到的差异，以及在未来研究中使用这种突变之前需要仔细审查。