Shibayama Naoya, Miura Shigetoshi, Tame Jeremy R H, Yonetani Takashi, Park Sam-Yong
Department of Physiology, Division of Biophysics, Jichi Medical School, Yakushiji 3311-1, Minamikawachi, Kawachi, Tochigi 329-0498, Japan.
J Biol Chem. 2002 Oct 11;277(41):38791-6. doi: 10.1074/jbc.M205461200. Epub 2002 Jul 16.
Bezafibrate, an antilipidemic drug, is known as a potent allosteric effector of hemoglobin. The previously proposed mechanism for the allosteric potency of this drug was that it stabilizes and constrains the T-state of hemoglobin by specifically binding to the large central cavity of the T-state. Here we report a new allosteric binding site of fully liganded R-state hemoglobin for this drug. The high resolution crystal structure of horse carbonmonoxyhemoglobin in complex with bezafibrate reveals that the bezafibrate molecule lies near the surface of the E-helix of each alpha subunit and the complex maintains the quaternary structure of the R-state. Binding is caused by the close fit of bezafibrate into the binding pocket, which is composed of some hydrophobic residues and the heme edge, suggesting the importance of hydrophobic interactions. Upon binding of bezafibrate, the distance between Fe and the N epsilon(2) of distal His E7(alpha 58) is shortened by 0.22 A in the alpha subunit, whereas no significant structural changes are transmitted to the beta subunit. Oxygen equilibrium studies of R-state-locked hemoglobin with bezafibrate in a wet porous sol-gel indicate that bezafibrate selectively lowers the oxygen affinity of one type of subunit within the R-state, consistent with the structural data. These results disclose a new allosteric mechanism of bezafibrate and offer the first demonstration of how the allosteric effector interacts with R-state hemoglobin.
苯扎贝特是一种抗血脂药物，已知是血红蛋白的一种强效变构效应剂。先前提出的该药物变构效力机制是，它通过特异性结合到T态的大中央腔来稳定并限制血红蛋白的T态。在此我们报道了该药物与完全配体化的R态血红蛋白的一个新的变构结合位点。马碳氧血红蛋白与苯扎贝特复合物的高分辨率晶体结构表明，苯扎贝特分子位于每个α亚基E螺旋的表面附近，且该复合物维持R态的四级结构。结合是由于苯扎贝特紧密契合到由一些疏水残基和血红素边缘组成的结合口袋中，这表明疏水相互作用的重要性。苯扎贝特结合后，α亚基中Fe与远端His E7（α58）的Nε(2)之间的距离缩短了0.22 Å，而没有明显的结构变化传递到β亚基。在湿多孔溶胶 - 凝胶中对R态锁定的血红蛋白与苯扎贝特进行的氧平衡研究表明，苯扎贝特选择性降低R态内一种亚基类型的氧亲和力，这与结构数据一致。这些结果揭示了苯扎贝特一种新的变构机制，并首次证明了变构效应剂如何与R态血红蛋白相互作用。
