Conformational interconversion in protein crystals.
Conformational interconversion in protein crystals.
复制标题
蛋白质晶体中的构象相互转换。
DOI：
10.1016/0022-2836(92)90584-7
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发表时间：
1992
影响因子：
5.6
通讯作者：
Champion,PM
中科院分区：
文献类型：
--
作者：
Zhu,L;Sage,JT;Rigos,AA;Morikis,D;Champion,PM
我们提出的证据表明，碳一氧肌红蛋白晶体的结构可以通过降低pH值来改变。这种结构变化是由特征Fe → CO拉曼模式在508和491 cm− 1监测，并被认为涉及一个本地化的远端口袋过渡从“封闭”构象在pH 7到一个更“开放”的构象在pH 4。这些变化发生在晶体中，但不会损失252 cm-1处的构象敏感拉曼模式的强度，该模式表明溶液中球蛋白结构的部分解折叠。定量研究，监测开放和封闭的群体作为激光光解的函数，表明在298 K的溶液中的相互转换速率（k±）与光解和CO进入速率（即k± 103 s −1）相比是快的，而在冷冻样品中的相互转换比实验时间尺度（分钟）慢得多。由于开放构象是一个少数物种在pH值为7，在水溶液中的快速交换是一个必要条件，这种物种发挥功能的作用。在晶体中，与溶液相比，相互转化速率变慢，开始接近光解速率（即k±~ 103至104 s −1）。这表明，构象交换的障碍增加了在晶体环境中，相比的解决方案，显然是由于周围分子的包装力。需要在高pH和低pH下对MbCO晶体进行X射线和中子衍射研究，以表征结构变化的细节，并测试封闭和开放的远端口袋结构与508和491 cm− 1 Fe MbCO模式相关的假设。
We present evidence that the structure of carbonmonoxy myoglobin crystals can be altered by lowering the pH. This structural change is monitored by the characteristic FeCO Raman modes at 508 and 491 cm−1and is thought to involve a localized distal pocket transition from a “closed” conformation at pH 7 to a more “open” conformation at pH 4. These changes take place in the crystal without loss of intensity of a conformationally sensitive Raman mode at 252 cm−1that signals a partial unfolding of the globin structure in solution. Quantitative studies, which monitor the open and closed populations as a function of laser photolysis, demonstrate that the interconversion rates (k±) in solution at 298 K are fast compared to the photolysis and CO entry rates (i.e.k±⪢ 103s−1), while in frozen samples the interconversion is much slower than the experimental time scale (minutes). Since the open conformation is a minority species at pH 7, rapid exchange in aqueous solution is a necessary condition for this species to play a functional role. In the crystal, the interconversion rates are slowed compared to solution and begin to approach the photolysis rate (i.e.k±~ 103to 104s−1). This indicates that the barriers for conformational exchange are increased in the crystal environment, compared to the solution, apparently due to the packing forces of the surrounding molecules. X-ray and neutron diffraction studies of MbCO crystals at high and low pH are needed to characterize the details of the structural changes and to test the hypothesis that closed and open distal pocket structures are associated with the 508 and 491 cm−1FeCO modes.