Hekmat Azadeh, Hajebrahimi Zahra, Motamedzade Amir
Department of Biology, Science and Research Branch, Islamic Azad University, Tehran. Iran.
Aerospace Research Institute, Ministry of Science Research and Technology, Tehran. Iran.
Protein Pept Lett. 2017;24(11):1030-1039. doi: 10.2174/0929866524666170918111038.
Nowadays, the biological effects of microgravity have been the subject of various experimental researches. Microgravity has been confirmed to affect biological systems. Furthermore, as a result of improvement in space technology for instance a manned mission to the moon, probabilities for human exposed to microgravity have incremented undoubtedly.
The purpose of this study was to investigate the probable biological effects of microgravity on the human serum albumin (HSA) structure after 3 and 24 h exposure. It is worth mentioning that this is the first effort to investigate the structural alternations of HSA under simulated microgravity condition in biophysico-chemical terms thru different spectroscopic instruments.
2D clinostat was utilized for simulating microgravity. The UV-Vis, intrinsic and extrinsic fluorescence, dynamic light scattering (DLS) and circular dichroism (CD) spectra of 3.76 µM HSA in Tris-HCl buffer (pH 7.4, 0.1 M) and 3.76 µM HSA in Tris-HCl buffer (pH 7.4, 0.1 M) kept at simulated microgravity for 3 and 24h were verified.
The UV-Visible, near-UV-CD and intrinsic fluorescence spectroscopy represented that microgravity can remarkably change the tertiary structure of HSA. Additionally, the ANS affinity for HSA incremented when the protein was exposed to simulate microgravity compared to unexposed HSA, which may possibly have appeared attributable to expansion of the structure of simulated HSA. Fluorescence quenching by acrylamide demonstrated higher stern-volmer constant for exposed HSA. The results of zeta potential and dynamic light scattering (DLS) experiments depicted that simulated microgravity cause raise in the surface charge and size of HSA. Far-UV CD data demonstrated that simulated microgravity did not perturb the secondary structures of the protein.
Collectively, our results suggest that HSA after 24 h exposure to microgravity can exhibit a molten globule (MG) structure. This is the first report to demonstrate the molten globule state formation in microgravity condition. Results from this study could give knowledge to understand the role of gravity on protein folding process. In addition, this finding could help to find out safe limits for astronauts and space travelers and to develop adequate countermeasures against any harmful effects of microgravity.
如今，微重力的生物学效应已成为各种实验研究的主题。微重力已被证实会影响生物系统。此外，随着太空技术的进步，例如载人登月任务，人类暴露于微重力的可能性无疑增加了。
本研究的目的是调查暴露3小时和24小时后微重力对人血清白蛋白（HSA）结构可能产生的生物学效应。值得一提的是，这是首次通过不同的光谱仪器从生物物理化学角度研究模拟微重力条件下HSA的结构变化。
使用二维回转器模拟微重力。对在Tris-HCl缓冲液（pH 7.4，0.1 M）中浓度为3.76 μM的HSA以及在模拟微重力条件下保持3小时和24小时的Tris-HCl缓冲液（pH 7.4，0.1 M）中的3.76 μM HSA的紫外可见光谱、内源和外源荧光光谱、动态光散射（DLS）光谱和圆二色性（CD）光谱进行了验证。
紫外可见光谱法、近紫外圆二色光谱法和内源荧光光谱法表明，微重力可显著改变HSA的三级结构。此外，与未暴露的HSA相比，当蛋白质暴露于模拟微重力时，ANS对HSA的亲和力增加，这可能是由于模拟HSA结构的扩展所致。丙烯酰胺荧光猝灭实验表明，暴露的HSA具有更高的斯特恩-沃尔默常数。zeta电位和动态光散射（DLS）实验结果表明，模拟微重力导致HSA的表面电荷和尺寸增加。远紫外CD数据表明，模拟微重力不会干扰蛋白质的二级结构。
总体而言，我们的结果表明，暴露于微重力24小时后的HSA可呈现熔融球状体（MG）结构。这是第一份证明在微重力条件下形成熔融球状体状态的报告。本研究结果有助于了解重力在蛋白质折叠过程中的作用。此外，这一发现有助于确定宇航员和太空旅行者的安全限度，并制定适当的对策以应对微重力的任何有害影响。
