Barren Brandy, Gakhar Lokesh, Muradov Hakim, Boyd Kimberly K, Ramaswamy S, Artemyev Nikolai O
Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA, USA.
EMBO J. 2009 Nov 18;28(22):3613-22. doi: 10.1038/emboj.2009.284. Epub 2009 Oct 1.
The inhibitory interaction of phosphodiesterase-6 (PDE6) with its gamma-subunit (Pgamma) is pivotal in vertebrate phototransduction. Here, crystal structures of a chimaeric PDE5/PDE6 catalytic domain (PDE5/6cd) complexed with sildenafil or 3-isobutyl-1-methylxanthine and the Pgamma-inhibitory peptide Pgamma(70-87) have been determined at 2.9 and 3.0 A, respectively. These structures show the determinants and the mechanism of the PDE6 inhibition by Pgamma and suggest the conformational change of Pgamma on transducin activation. Two variable H- and M-loops of PDE5/6cd form a distinct interface that contributes to the Pgamma-binding site. This allows the Pgamma C-terminus to fit into the opening of the catalytic pocket, blocking cGMP access to the active site. Our analysis suggests that disruption of the H-M loop interface and Pgamma-binding site is a molecular cause of retinal degeneration in atrd3 mice. Comparison of the two PDE5/6cd structures shows an overlap between the sildenafil and Pgamma(70-87)-binding sites, thereby providing critical insights into the side effects of PDE5 inhibitors on vision.
磷酸二酯酶6（PDE6）与其γ亚基（Pγ）之间的抑制性相互作用在脊椎动物光转导中起关键作用。在此，分别以2.9 Å和3.0 Å的分辨率确定了与西地那非或3-异丁基-1-甲基黄嘌呤以及Pγ抑制肽Pγ（70-87）复合的嵌合PDE5/PDE6催化结构域（PDE5/6cd）的晶体结构。这些结构展示了Pγ抑制PDE6的决定因素和机制，并提示了转导素激活时Pγ的构象变化。PDE5/6cd的两个可变H环和M环形成了一个独特的界面，该界面构成了Pγ结合位点。这使得Pγ的C末端能够契合到催化口袋的开口处，阻止cGMP进入活性位点。我们的分析表明，H-M环界面和Pγ结合位点的破坏是atrd3小鼠视网膜退化的分子原因。对两种PDE5/6cd结构的比较显示西地那非和Pγ（70-87）结合位点之间存在重叠，从而为PDE5抑制剂对视力的副作用提供了关键见解。
