...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Biochemistry >Formation of a long-lived photoproduct with a deprotonated Schiff base in proteorhodopsin, and its enhancement by mutation of Asp227
【24h】

Formation of a long-lived photoproduct with a deprotonated Schiff base in proteorhodopsin, and its enhancement by mutation of Asp227

机译：蛋白视紫红质中带有去质子化席夫碱的长寿命光产物的形成及其通过Asp227突变的增强

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Proteorhodopsin, a retinal protein of marine proteobacteria similar to bacteriorhodopsin of the archaea, is a light-driven proton pump. Absorption of a light quantum initiates a reaction cycle (turnover time of ca. 50 ms), which includes photoisomerization of the retinal from the all-trans to the 13-cis form and transient deprotonation of the retinal Schiff base, followed by recovery of the initial state. We report here that in addition to this fast cyclic conversion, illumination at high pH results in accumulation of a long-lived photoproduct absorbing at 362 nm. This photoconversion is much more efficient in the D227N mutant in which the anionic Asp227, which together with Asp97 constitutes the Schiff base counterion, is replaced with a neutral residue. Upon illumination at pH 8.5, most of the D227N pigment is converted to the 362 nm species, with a quantum efficiency of ca. 0.2. The pK(a) for this transition in the wild type is 9.6, but decreased to 7.5 after mutation of Asp227. The short wavelength of the absorption maximum of the photoproduct indicates that it has a deprotonated Schiff base. In the dark, this photoproduct is converted back to the initial pigment with a time constant of 30 min (in D227N, at pH 8.5), but it can be reconverted more rapidly by illumination with near-UV light. Experiments with "locked" retinal analogues which selectively exclude rotation around either the C9=C10, C11=C12, or C13=C14 bond show that formation of the 362 nm species involves isomerization around the C13=C14 bond. In agreement with this, retinal extraction indicates that the 362 nm photoproduct is 13-cis whereas the initial state is predominantly all-trans. A rapid shift of the pH from 8.5 to 4 greatly accelerates thermal reconversion of the 362 nm species to the initial pigment, suggesting that its recovery involving the thermal isomerization of the chromophore is controlled by ionizable residues, primarily the Schiff base and Asp97. The transformation to the long-lived 362 nm photoproduct is apparently a side reaction of the photocycle, a response to high pH, caused by alteration of the normal reprotonation and reisomerization pathway of the Schiff base.
机译：视紫红质是海洋细菌的一种视网膜蛋白，类似于古细菌的视紫红质，是一种光驱动的质子泵。吸收光量子会启动一个反应周期（约50毫秒的转换时间），其中包括视网膜从全反式变为13-顺式的光异构化以及视网膜席夫碱的短暂去质子化，然后恢复初始状态。我们在这里报告说，除了这种快速的循环转化，在高pH值下的照明还会导致长寿命的光产物在362 nm处吸收并积累。这种光转化在D227N突变体中更为有效，在该突变体中，阴离子Asp227与Asp97一起构成席夫碱抗衡离子，被中性残基取代。在pH 8.5照射下，大多数D227N颜料被转换为362 nm物质，量子效率约为。 0.2。野生型中此过渡的pK（a）为9.6，但在Asp227突变后降低到7.5。光产物最大吸收的短波长表明它具有去质子化的席夫碱。在黑暗中，此光产物会以30分钟的时间常数（在D227N中，pH 8.5）转换回初始颜料，但可以通过近紫外光照射更快地将其转换。用“锁定的”视网膜类似物进行的实验可以选择性地排除围绕C9 = C10，C11 = C12或C13 = C14键的旋转，表明362 nm物种的形成涉及C13 = C14键周围的异构化。与此相符，视网膜提取表明362 nm的光产物是13-顺式，而初始状态主要是全反式的。 pH从8.5到4的快速变化极大地促进了362 nm物质向初始颜料的热转化，这表明其回收与发色团的热异构化有关，主要受可电离的残基控制，主要是席夫碱和Asp97。向长寿命362 nm光产物的转化显然是光循环的副反应，是对高pH的响应，这是由于席夫碱的正常质子化和再异构化途径的改变而引起的。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号