Hwang Ji-Young, Lange Christian, Helten Andreas, Höppner-Heitmann Doris, Duda Teresa, Sharma Rameshwar K, Koch Karl-Wilhelm
Institut für Biologische Informationsverarbeitung 1, Forschungszentrum Jülich, Jülich, Germany.
Eur J Biochem. 2003 Sep;270(18):3814-21. doi: 10.1046/j.1432-1033.2003.03770.x.
In rod phototransduction, cyclic GMP synthesis by membrane bound guanylate cyclase ROS-GC1 is under Ca(2+)-dependent negative feedback control mediated by guanylate cyclase-activating proteins, GCAP-1 and GCAP-2. The cellular concentration of GCAP-1 and GCAP-2 approximately sums to the cellular concentration of a functional ROS-GC1 dimer. Both GCAPs increase the catalytic efficiency (kcat/Km) of ROS-GC1. However, the presence of a myristoyl group in GCAP-1 has a strong impact on the regulation of ROS-GC1, this is in contrast to GCAP-2. Catalytic efficiency of ROS-GC1 increases 25-fold when it is reconstituted with myristoylated GCAP-1, but only by a factor of 3.4 with nonmyristoylated GCAP-1. In contrast to GCAP1, myristoylation of GCAP-2 has only a minor effect on kcat/Km. The increase with both myristoylated and nonmyristoylated GCAP-2 is 10 to 13-fold. GCAPs also confer different Ca(2+)-sensitivities to ROS-GC1. Activation of the cyclase by GCAP-1 is half-maximal at 707 nM free [Ca(2+)], while that by GCAP-2 is at 100 nM. The findings show that differences in catalytic efficiency and Ca(2+)-sensitivity of ROS-GC1 are conferred by GCAP-1 and GCAP-2. The results further indicate the concerted operation of two 'GCAP modes' that would extend the dynamic range of cyclase regulation within the physiological range of free cytoplasmic Ca(2+) in photoreceptor cells.
在视杆细胞光转导过程中，膜结合鸟苷酸环化酶ROS - GC1合成环鸟苷酸受到鸟苷酸环化酶激活蛋白GCAP - 1和GCAP - 2介导的钙依赖性负反馈控制。GCAP - 1和GCAP - 2的细胞浓度之和大约等于功能性ROS - GC1二聚体的细胞浓度。两种GCAP都能提高ROS - GC1的催化效率（kcat/Km）。然而，GCAP - 1中肉豆蔻酰基的存在对ROS - GC1的调节有强烈影响，这与GCAP - 2不同。当ROS - GC1与肉豆蔻酰化的GCAP - 1重组时，其催化效率提高25倍，但与非肉豆蔻酰化的GCAP - 1重组时仅提高3.4倍。与GCAP1不同，GCAP - 2的肉豆蔻酰化对kcat/Km只有轻微影响。肉豆蔻酰化和非肉豆蔻酰化的GCAP - 2使催化效率提高10至13倍。GCAP还赋予ROS - GC1不同的钙敏感性。GCAP - 1激活环化酶的半最大效应浓度为游离[Ca(2 +)]707 nM，而GCAP - 2为100 nM。这些发现表明，ROS - GC1催化效率和钙敏感性的差异是由GCAP - 1和GCAP - 2造成的。结果进一步表明两种“GCAP模式”协同作用，可在光感受器细胞游离细胞质钙的生理范围内扩展环化酶调节的动态范围。
