Department of Physiology and Pharmacology , Karolinska Institutet , SE-171 77 Stockholm , Sweden.
Nano Lett. 2018 Nov 14;18(11):7021-7029. doi: 10.1021/acs.nanolett.8b02989. Epub 2018 Oct 23.
Ions greatly influence protein structure-function and are critical to health and disease. A 10, 000-fold higher calcium in the sarcoplasmic reticulum (SR) of muscle suggests elevated calcium levels near active calcium channels at the SR membrane and the impact of localized high calcium on the structure-function of the motor protein myosin. In the current study, combined quantum dot (QD)-based nanothermometry and circular dichroism (CD) spectroscopy enabled detection of previously unknown enthalpy changes and associated structural remodeling of myosin, impacting its function following exposure to elevated calcium. Cadmium telluride QDs adhere to myosin, function as thermal sensors, and reveal that exposure of myosin to calcium is exothermic, resulting in lowering of enthalpy, a decrease in alpha helical content measured using CD spectroscopy, and the consequent increase in motor efficiency. Isolated muscle fibers subjected to elevated levels of calcium further demonstrate fiber lengthening and decreased motility of actin filaments on myosin-functionalized substrates. Our results, in addition to providing new insights into our understanding of muscle structure-function, establish a novel approach to understand the enthalpy of protein-ion interactions and the accompanying structural changes that may occur within the protein molecule.
离子对蛋白质结构-功能有很大影响，对健康和疾病至关重要。肌肉肌浆网 (SR) 中的钙离子浓度比正常情况下高出 10,000 倍，这表明在 SR 膜上的活性钙通道附近的钙离子浓度升高，以及局部高钙对肌球蛋白这种运动蛋白的结构-功能的影响。在本研究中，结合量子点 (QD) 纳米温度计和圆二色性 (CD) 光谱技术，能够检测到以前未知的焓变，以及肌球蛋白的结构重塑，这会影响其在暴露于高钙环境后的功能。碲化镉 QD 与肌球蛋白结合，作为热传感器，结果表明肌球蛋白暴露于钙是放热的，导致焓降低，使用 CD 光谱测量的α螺旋含量减少，以及随之而来的运动效率提高。在肌肉纤维中升高钙水平，进一步证明肌球蛋白功能化底物上的肌动蛋白丝纤维伸长和运动性降低。我们的研究结果除了为理解肌肉结构-功能提供新的见解外，还建立了一种新的方法来理解蛋白质-离子相互作用的焓以及可能在蛋白质分子内发生的结构变化。
