Allosteric modulation of hormone release from thyroxine and corticosteroid-binding globulins.
Allosteric modulation of hormone release from thyroxine and corticosteroid-binding globulins.
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DOI：
10.1074/jbc.m110.171082
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发表时间：
2011-05-06
期刊：
影响因子：
--
通讯作者：
Zhou A
中科院分区：
文献类型：
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作者：
Qi X;Loiseau F;Chan WL;Yan Y;Wei Z;Milroy LG;Myers RM;Ley SV;Read RJ;Carrell RW;Zhou A
甲状腺素结合球蛋白（TBG）和皮质类固醇结合球蛋白（CBG）的激素释放受反应性中心环进出分子β- A片的运动调节。为了研究这些变化是如何传递到激素结合位点的，我们使用合成的甲状腺素荧光团开发了一种灵敏的检测方法，并解决了反应性环裂TBG及其与甲状腺素、甲状腺素荧光团、速尿和甲氧胺酸配合物的晶体结构。反应性环的切割导致其完全插入β-薄片A，并在TBG和CBG中显著但不完全地降低结合亲和力。我们在这里表明，反应环的残基Thr342和激素结合位点的Tyr241之间的直接相互作用有助于反应环插入后甲状腺素的结合和释放。然而，更大的变构效应是由于连接环拉伸到D螺旋（hD）的顶部，正如在TBG中证实的那样，环缩短了三个残基，使其对s到r转变不敏感。hD环的变化传递到结合袋中涉及到由Lys243连接到hD环的s2/3B环的一致运动，而后者又由Arg378连接到甲状腺素结合位点两侧的s4/5B环。总的来说，反应环、hD和激素结合位点的协调运动允许激素释放的变构调节，正如这里所展示的对温度变化的调节。
The release of hormones from thyroxine-binding globulin (TBG) and corticosteroid-binding globulin (CBG) is regulated by movement of the reactive center loop in and out of the β-sheet A of the molecule. To investigate how these changes are transmitted to the hormone-binding site, we developed a sensitive assay using a synthesized thyroxine fluorophore and solved the crystal structures of reactive loop cleaved TBG together with its complexes with thyroxine, the thyroxine fluorophores, furosemide, and mefenamic acid. Cleavage of the reactive loop results in its complete insertion into the β-sheet A and a substantial but incomplete decrease in binding affinity in both TBG and CBG. We show here that the direct interaction between residue Thr342 of the reactive loop and Tyr241 of the hormone binding site contributes to thyroxine binding and release following reactive loop insertion. However, a much larger effect occurs allosterically due to stretching of the connecting loop to the top of the D helix (hD), as confirmed in TBG with shortening of the loop by three residues, making it insensitive to the S-to-R transition. The transmission of the changes in the hD loop to the binding pocket is seen to involve coherent movements in the s2/3B loop linked to the hD loop by Lys243, which is, in turn, linked to the s4/5B loop, flanking the thyroxine-binding site, by Arg378. Overall, the coordinated movements of the reactive loop, hD, and the hormone binding site allow the allosteric regulation of hormone release, as with the modulation demonstrated here in response to changes in temperature.