Townsend Philip D, Holliday Phillip M, Fenyk Stepan, Hess Kenneth C, Gray Michael A, Hodgson David R W, Cann Martin J
School of Biological and Biomedical Sciences, Durham University, Durham, UK.
J Biol Chem. 2009 Jan 9;284(2):784-91. doi: 10.1074/jbc.M807239200. Epub 2008 Nov 13.
Carbon dioxide is fundamental to the physiology of all organisms. There is considerable interest in the precise molecular mechanisms that organisms use to directly sense CO(2). Here we demonstrate that a mammalian recombinant G-protein-activated adenylyl cyclase and the related Rv1625c adenylyl cyclase of Mycobacterium tuberculosis are specifically stimulated by CO(2). Stimulation occurred at physiological concentrations of CO(2) through increased k(cat). CO(2) increased the affinity of enzyme for metal co-factor, but contact with metal was not necessary as CO(2) interacted directly with apoenzyme. CO(2) stimulated the activity of both G-protein-regulated adenylyl cyclases and Rv1625c in vivo. Activation of G-protein regulated adenylyl cyclases by CO(2) gave a corresponding increase in cAMP-response element-binding protein (CREB) phosphorylation. Comparison of the responses of the G-protein regulated adenylyl cyclases and the molecularly, and biochemically distinct mammalian soluble adenylyl cyclase revealed that whereas G-protein-regulated enzymes are responsive to CO(2), the soluble adenylyl cyclase is responsive to both CO(2) and bicarbonate ion. We have, thus, identified a signaling enzyme by which eukaryotes can directly detect and respond to fluctuating CO(2).
二氧化碳是所有生物体生理活动的基础。人们对生物体用于直接感知二氧化碳的精确分子机制有着浓厚的兴趣。在此，我们证明哺乳动物重组G蛋白激活的腺苷酸环化酶以及结核分枝杆菌相关的Rv1625c腺苷酸环化酶受到二氧化碳的特异性刺激。在生理浓度的二氧化碳条件下，通过增加催化常数（kcat）实现刺激作用。二氧化碳增加了酶对金属辅因子的亲和力，但由于二氧化碳直接与脱辅基酶相互作用，所以与金属接触并非必要条件。在体内，二氧化碳刺激了G蛋白调节的腺苷酸环化酶和Rv1625c的活性。二氧化碳对G蛋白调节的腺苷酸环化酶的激活导致环磷酸腺苷反应元件结合蛋白（CREB）磷酸化相应增加。对G蛋白调节的腺苷酸环化酶与分子结构和生化特性不同的哺乳动物可溶性腺苷酸环化酶的反应进行比较发现，虽然G蛋白调节的酶对二氧化碳有反应，但可溶性腺苷酸环化酶对二氧化碳和碳酸氢根离子都有反应。因此，我们鉴定出了一种信号酶，真核生物可通过它直接检测并响应波动的二氧化碳。
