Kotera Jun, Francis Sharron H, Grimes Kennard A, Rouse Alfreda, Blount Mitsi A, Corbin Jackie D
Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232-0615, USA.
Front Biosci. 2004 Jan 1;9:378-86. doi: 10.2741/1231.
Phosphodiesterase-5 (PDE5) and cGMP-dependent protein kinase (PKG) play key roles in cGMP signaling. PDE5 has a catalytic domain (C domain) that hydrolyzes cGMP and a regulatory domain (R domain) that binds cGMP at allosteric sites. We recently demonstrated that in corpus cavernosum, PDE5 concentration exceeds basal cGMP by ~5-fold making it possible that its allosteric sites could bind a significant fraction of the total cellular cGMP. It is hypothesized that the allosteric sites regulate cGMP signaling by sequestering cGMP. At 60 nM cGMP in vitro, which approaches a stimulated concentration of cGMP in rabbit corpus cavernosum, isolated R domain inhibits both cGMP hydrolysis by C domain and activation of PKG (IC50 values of 388 and 100 nM, respectively). Prior phosphorylation of R domain by cyclic nucleotide-dependent protein kinases, which increases its cGMP-binding affinity, also increases its potency for inhibiting both cGMP hydrolysis by C domain and cGMP activation of PKG (IC50 values of 58 and 38 nM, respectively). In rabbit corpus cavernosum, PDE5 concentration (94 nM) exceeds these values. These findings support our hypothesis that physiological concentrations of R domain regulate cGMP signaling by sequestering this nucleotide and that phosphorylation of R domain modulates this effect. This could provide for negative feedback control of cGMP-signaling.
磷酸二酯酶-5（PDE5）和环磷酸鸟苷依赖性蛋白激酶（PKG）在环磷酸鸟苷信号传导中起关键作用。PDE5具有一个催化结构域（C结构域），可水解环磷酸鸟苷，还有一个调节结构域（R结构域），可在变构位点结合环磷酸鸟苷。我们最近证明，在海绵体中，PDE5的浓度比基础环磷酸鸟苷高出约5倍，这使得其变构位点有可能结合细胞内环磷酸鸟苷总量的很大一部分。据推测，变构位点通过隔离环磷酸鸟苷来调节环磷酸鸟苷信号传导。在体外60 nM的环磷酸鸟苷浓度下（接近兔海绵体中环磷酸鸟苷的刺激浓度），分离出的R结构域可抑制C结构域对环磷酸鸟苷的水解以及PKG的激活（IC50值分别为388和100 nM）。环核苷酸依赖性蛋白激酶对R结构域的预先磷酸化可增加其与环磷酸鸟苷的结合亲和力，同时也增强了其抑制C结构域对环磷酸鸟苷水解以及环磷酸鸟苷激活PKG的能力（IC50值分别为58和38 nM）。在兔海绵体中，PDE5的浓度（94 nM）超过了这些值。这些发现支持了我们的假设，即R结构域的生理浓度通过隔离这种核苷酸来调节环磷酸鸟苷信号传导，并且R结构域的磷酸化调节了这种作用。这可能为环磷酸鸟苷信号传导提供负反馈控制。
