Ferreira Jacob, Belliveau Hayden, Steegborn Clemens, Buck Jochen, Levin Lonny R
Department of Pharmacology, Weill Cornell Medicine, New York, NY 10065, USA.
Department of Biochemistry, University of Bayreuth, 95440 Bayreuth, Germany.
Int J Mol Sci. 2025 Jul 3;26(13):6401. doi: 10.3390/ijms26136401.
Soluble adenylyl cyclase (sAC) is molecularly and biochemically distinct from other mammalian nucleotidyl cyclases. It is uniquely regulated directly by bicarbonate (HCO) and calcium (Ca) ions and is responsive to physiologic fluctuations in levels of its substrate, adenosine triphosphate (ATP). Our initial in vitro biochemical studies suggested two mechanisms for HCO-dependent elevation of sAC activity: increasing catalytic rate and relieving inhibition observed in the presence of supraphysiological levels of substrate, ATP. Structural and mutational studies revealed that HCO increases catalytic rate via the disruption of a salt bridge that facilitates productive interactions with the substrate. Here, we demonstrate that the HCO stimulation observed under supraphysiological ATP concentrations is due to the mitigation of ATP-dependent acidification. Therefore, we conclude that the sole physiologically relevant mechanism of HCO regulation of sAC is through its pH-independent effect facilitating productive substrate binding to the catalytic site.
可溶性腺苷酸环化酶（sAC）在分子和生化方面与其他哺乳动物核苷酸环化酶不同。它独特地直接受碳酸氢根（HCO）和钙离子（Ca）调节，并对其底物三磷酸腺苷（ATP）水平的生理波动有反应。我们最初的体外生化研究提出了两种HCO依赖的sAC活性升高机制：增加催化速率和缓解在超生理水平底物ATP存在下观察到的抑制作用。结构和突变研究表明，HCO通过破坏促进与底物有效相互作用的盐桥来增加催化速率。在这里，我们证明在超生理ATP浓度下观察到的HCO刺激是由于ATP依赖性酸化的减轻。因此，我们得出结论，HCO调节sAC的唯一生理相关机制是通过其不依赖pH的效应促进底物与催化位点的有效结合。
