Life Sciences, Soka University of America, Aliso Viejo, CA 92656, USA.
Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA 93106-5100, USA.
Int J Mol Sci. 2024 Aug 17;25(16):8954. doi: 10.3390/ijms25168954.
Reflectin is a cationic, block copolymeric protein that mediates the dynamic fine-tuning of color and brightness of light reflected from nanostructured Bragg reflectors in iridocyte skin cells of squids. In vivo, the neuronally activated phosphorylation of reflectin triggers its assembly, driving osmotic dehydration of the membrane-bounded Bragg lamellae containing the protein to simultaneously shrink the lamellar thickness and spacing while increasing their refractive index contrast, thus tuning the wavelength and increasing the brightness of reflectance. In vitro, we show that the reduction in repulsive net charge of the purified, recombinant reflectin-either (for the first time) by generalized anionic screening with salt or by pH titration-drives a finely tuned, precisely calibrated increase in the size of the resulting multimeric assemblies. The calculated effects of phosphorylation in vivo are consistent with these effects observed in vitro. The precise proportionality between the assembly size and charge neutralization is enabled by the demonstrated rapid dynamic arrest of multimer growth by a continual, equilibrium tuning of the balance between the protein's Coulombic repulsion and short-range interactive forces. The resulting stability of reflectin assemblies with time ensures a reciprocally precise control of the particle number concentration, encoding a precise calibration between the extent of neuronal signaling, osmotic pressure, and the resulting optical changes. The charge regulation of reflectin assembly precisely fine-tunes a colligative property-based nanostructured biological machine. A physical mechanism is proposed.
反射蛋白是一种阳离子型嵌段共聚物蛋白质，它介导了鱿鱼的虹细胞中纳米结构布拉格反射器所反射光的颜色和亮度的动态微调。在体内，反射蛋白的神经元激活磷酸化触发其组装，驱动含有该蛋白的膜结合布拉格层的渗透脱水，同时缩小层状厚度和间距，同时增加其折射率对比度，从而调整波长并增加反射率的亮度。在体外，我们表明，纯化的重组反射蛋白的排斥净电荷减少——无论是通过盐的广义阴离子屏蔽（这是首次）还是通过 pH 滴定——都会导致多聚体组装体的大小精细而精确地增加。体内磷酸化的计算效应与体外观察到的这些效应一致。在组装体大小和电荷中和之间的精确比例关系是通过证明多聚体生长的快速动态阻滞来实现的，这种阻滞通过不断平衡蛋白质的库仑斥力和短程相互作用力之间的平衡来实现。随着时间的推移，反射蛋白组装体的稳定性确保了颗粒数浓度的相互精确控制，从而在神经元信号传递、渗透压和由此产生的光学变化之间实现了精确的校准。反射蛋白组装体的电荷调节精确地微调了基于依数性的纳米结构生物机器。提出了一种物理机制。
