Molecular mechanism of reflectin's tunable biophotonic control: Opportunities and limitations for new optoelectronics
Molecular mechanism of reflectin's tunable biophotonic control: Opportunities and limitations for new optoelectronics
复制标题
DOI：
10.1063/1.4985758
复制
发表时间：
2017-10-01
期刊：
影响因子：
6.1
通讯作者：
Morse, Daniel E.
中科院分区：
文献类型：
--
作者：
Levenson, Robert;DeMartini, Daniel G.;Morse, Daniel E.
在某些鱿鱼的反射皮肤细胞中，反射蛋白填充了动态可调的布拉格片层，这一发现促使人们努力设计新的受反射启发的动态光子学系统。但是，对反射镜的实际作用和作用机制的新见解限制并更好地定义了合理设计基于反射镜组件的光学系统的机会和局限性。我们和我们的同事已经发现，反射蛋白的功能就像一个信号控制的分子机器，调节渗透马达，调节脂质鱿鱼虹膜细胞中可调节的、膜结合的Bragg片的厚度、间距和折射率。可调反射蛋白的特点是具有可变数量的高度保守的肽结构域，这些结构域散布着带正电的连接体片段，它们在链内和链间的接触受到库仑斥力的限制。生理上，这种抑制逐渐被乙酰胆碱（神经递质）诱导的位点特异性磷酸化所产生的电荷中和所克服，从而触发反射从红色到蓝色的同时激活和渐进调节。这个过程的细节已经通过纯化的重组反射物的体外分析，通过ph滴定控制电荷中和或突变作为体内磷酸化的替代品来解决。这些分析的结果表明，中和克服了库仑抑制，可逆和循环地触发了反射物的缩合和二次折叠，出现了先前隐藏的、相分离的疏水结构域，从而实现了分层组装。这种可调节的、可逆的、可循环的组件调节吉布斯-多南介导的Bragg片的渗透收缩或膨胀，从而调节反射率的亮度和颜色。我们最近的研究揭示了电荷中和程度与反射蛋白组件大小之间的直接关系，进一步解释了反射光强度和波长的协同效应。突变分析表明，控制反射蛋白结构转变的“开关”沿着蛋白质分布，而最近进化的可调反射蛋白的序列和结构与其祖先的不可调同源物的序列和结构的详细比较有助于确定控制可调性的特定结构决定因素。(C) 2017作者：
Discovery that reflectin proteins fill the dynamically tunable Bragg lamellae in the reflective skin cells of certain squids has prompted efforts to design new reflectin-inspired systems for dynamic photonics. But new insights into the actual role and mechanism of action of the reflectins constrain and better define the opportunities and limitations for rationally designing optical systems with reflectin-based components. We and our colleagues have discovered that the reflectins function as a signal-controlled molecular machine, regulating an osmotic motor that tunes the thickness, spacing, and refractive index of the tunable, membrane-bound Bragg lamellae in the iridocytes of the loliginid squids. The tunable reflectin proteins, characterized by a variable number of highly conserved peptide domains interspersed with positively charged linker segments, are restricted in intra-and inter-chain contacts by Coulombic repulsion. Physiologically, this inhibition is progressively overcome by charge-neutralization resulting from acetylcholine (neurotransmitter)-induced, site-specific phosphorylation, triggering the simultaneous activation and progressive tuning of reflectance from red to blue. Details of this process have been resolved through in vitro analyses of purified recombinant reflectins, controlling charge-neutralization by pH-titration or mutation as surrogates for the in vivo phosphorylation. Results of these analyses have shown that neutralization overcoming the Coulombic inhibition reversibly and cyclably triggers condensation and secondary folding of the reflectins, with the emergence of previously cryptic, phase-segregated hydrophobic domains enabling hierarchical assembly. This tunable, reversible, and cyclable assembly regulates the Gibbs-Donnan mediated osmotic shrinking or swelling of the Bragg lamellae that tunes the brightness and color of reflected light. Our most recent studies have revealed a direct relationship between the extent of charge neutralization and the size of the reflectin assemblies, further explaining the synergistic effects on the intensity and wavelength of reflected light. Mutational analyses show that the "switch" controlling reflectins' structural transitions is distributed along the protein, while detailed comparisons of the sequences and structures of the recently evolved tunable reflectins to those of their ancestral, non-tunable homologs are helping to identify the specific structural determinants governing tunability. (C) 2017 Author(s).