Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9111.
State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, People's Republic of China
J Neurosci. 2021 May 5;41(18):3948-3957. doi: 10.1523/JNEUROSCI.3019-20.2021. Epub 2021 Mar 31.
odorant receptors (Ors) are ligand gated ion channels composed of a common receptor subunit Or co-receptor (ORCO) and one of 62 "tuning" receptor subunits that confer odorant specificity to olfactory neuron responses. Like other sensory systems studied to date, exposing olfactory neurons to activating ligands results in reduced responses to subsequent exposures through a process called desensitization. We recently showed that phosphorylation of serine 289 on the common Or subunit ORCO is required for normal peak olfactory neuron responses. Dephosphorylation of this residue occurs on prolonged odorant exposure, and underlies the slow modulation of olfactory neuron responses we term "slow desensitization." Slow desensitization results in the reduction of peak olfactory neuron responses and flattening of dose-response curves, implicating changes in ORCO phosphorylation state as an important modulator of olfactory neuron responses. Here, we report the identification of the primary kinase responsible for ORCO phosphorylation, PKC98E. Antiserum localizes the kinase to the dendrites of the olfactory neurons. Deletion of the kinase from olfactory neurons in the naive state (the absence of prolonged odor exposure) reduces ORCO phosphorylation and reduces peak odorant responses without altering receptor localization or expression levels. Genetic rescue with a predicted to be constitutively active restores ORCO S289 phosphorylation and olfactory neuron sensitivity to the mutants in the naive state. However, the dominant kinase is defective for slow desensitization. Together, these findings reveal that PKC98E is an important regulator of ORCO receptors and olfactory neuron function. We have identified PKC98E as the kinase responsible for phosphorylation of the odorant receptor co-receptor (ORCO) at S289 that is required for normal odorant response kinetics of olfactory neurons. This is a significant step toward revealing the enzymology underlying the regulation of odorant response regulation in insects.
气味受体（Ors）是配体门控离子通道，由一个共同的受体亚基 Or 共受体（ORCO）和 62 个“调谐”受体亚基之一组成，这些亚基赋予嗅觉神经元对气味的特异性反应。与迄今为止研究过的其他感觉系统一样，暴露于激活配体的嗅觉神经元会导致随后的暴露反应减少，这一过程称为脱敏。我们最近表明，共同的 Or 亚基 ORCO 上丝氨酸 289 的磷酸化是正常峰值嗅觉神经元反应所必需的。该残基的去磷酸化发生在长时间的气味暴露下，是我们称之为“缓慢脱敏”的嗅觉神经元反应缓慢调节的基础。缓慢脱敏导致峰值嗅觉神经元反应的减少和剂量反应曲线的平坦化，表明 ORCO 磷酸化状态的变化是嗅觉神经元反应的重要调节剂。在这里，我们报告了鉴定负责 ORCO 磷酸化的主要激酶，PKC98E。抗血清将激酶定位于嗅觉神经元的树突。在未暴露于延长的气味（即缺乏延长的气味暴露）的情况下，从嗅觉神经元中删除激酶会降低 ORCO 磷酸化并降低峰值气味反应，而不会改变受体定位或表达水平。在幼稚状态下用预测的组成型活性的基因进行遗传挽救，恢复 ORCO S289 的磷酸化和嗅觉神经元对突变体的敏感性在幼稚状态下。然而，显性激酶对于缓慢脱敏是有缺陷的。总之，这些发现表明 PKC98E 是 ORCO 受体和嗅觉神经元功能的重要调节剂。我们已经确定 PKC98E 是负责 ORCO 共受体（ORCO）上 S289 磷酸化的激酶，该磷酸化对于嗅觉神经元正常的气味反应动力学是必需的。这是揭示昆虫气味反应调节的酶学基础的重要一步。
