为什么是11-cis-视网膜? 为什么眼睛里没有7-cis,9-cis或13-cis视网膜呢?
Sivakumar Sekharan1, Keiji Morokuma
1Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
Journal of the American Chemical Society
|October 27, 2011
概括
视网膜和视之间的静电相互作用解释了为什么11-cis-视网膜在视觉中被选择. 这项研究还提供了天然存在的9-cis-rhodopsin的证据.
科学领域:
- 生物化学 生物化学
- 计算化学的计算化学
- 视觉科学科学 视觉科学
背景情况:
- 对于11-cis-视网膜作为视觉颜料中主要染色体的自然选择的精确机制在视觉化学中仍然是一个未解决的难题.
- 了解各种视网膜异构体的作用对于破译视觉色素功能至关重要.
研究的目的:
- 在脊椎动物和无脊椎动物的视觉颜料中计算研究不同的cis-视网膜同位素 (7-cis, 9-cis, 11-cis, 13-cis) 的结构,稳定性,能量和光谱.
- 阐明控制11-cis-视网膜的自然选择的主要因素.
主要方法:
- 采用混合量子力学/分子力学 (QM/MM) 计算方法.
- 在牛,和鱼视觉颜料中分析了四种不同的cis-retinal异构体.
主要成果:
- 视网膜和奥普辛之间的静电相互作用是11-cis-retinal与其他异构体相比暗态选择的主要驱动因素.
- 在能量方面,9-cis-retinal与11-cis-retinal非常接近,这表明它以9-cis-rhodopsin的形式自然存在.
- 7-cis-视网膜表现出类似于巴托罗多普辛的结构重组,表明一个"颠倒"的全跨配置.
- 计算的吸收波长 (λmax) 显示了视网膜同位素中逐渐红色转移与减少的键长交替 (431nm为7-cis至508nm为13-cis).
结论:
- 由opsin提供的静电环境是选择11-cis-retinal的关键,解释了它在视觉中的作用.
- 11-cis和9-cis异构体之间的能量相似性支持自然界中9-cis-rhodopsin的存在.
- 计算分析提供了对视觉色素中各种视网膜异构体的光谱特性和结构动态的洞察.
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