Structural Changes of Human Serum Albumin (HSA) in Simulated Microgravity

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.