Partially charged chiral molecules act as spin filters, with preference for electron transport toward one type of spin (“up” or “down”), depending on their handedness. This effect is named the chiral induced spin selectivity (CISS) effect. A consequence of this phenomenon is spin polarization concomitant with electric polarization in chiral molecules. These findings were shown by adsorbing chiral molecules on magnetic surfaces and investigating the spin-exchange interaction between the surface and the chiral molecule. This field of study was developed using artificial chiral molecules. Here we used such magnetic surfaces to explore the importance of the intrinsic chiral properties of proteins in determining their stability. First, proteins were adsorbed on paramagnetic and ferromagnetic nanoparticles in a solution, and subsequently urea was gradually added to induce unfolding. The structural stability of proteins was assessed using two methods: bioluminescence measurements used to monitor the activity of the Luciferase enzyme, and fast spectroscopy detecting the distance between two chromophores implanted at the termini of a Barnase core. We found that interactions with magnetic materials altered the structural and functional resilience of the natively folded proteins, affecting their behavior under varying mild denaturing conditions. Minor structural disturbances at low urea concentrations were impeded in association with paramagnetic nanoparticles, whereas at higher urea concentrations, major structural deformation was hindered in association with ferromagnetic nanoparticles. These effects were attributed to spin exchange interactions due to differences in the magnetic imprinting properties of each type of nanoparticle. Additional measurements of proteins on macroscopic magnetic surfaces support this conclusion. The results imply a link between internal spin exchange interactions in a folded protein and its structural and functional integrity on magnetic surfaces. Together with the accumulating knowledge on CISS, our findings suggest that chirality and spin exchange interactions should be considered as additional factors governing protein structures.
Bibliographical noteFunding Information:
This study was supported by the Israel Science Foundation grant 1182/19 and the Zelman Cowen Academic Initiatives. Work of PG and ST was supported by Grant 31003A_175453 from the Swiss National Fund. Hadar Manis Levy would like to thank the EMBO postdoctoral fellowship ALTF 508-2022. In-doped Barium hexaferrite nanoparticles were synthesized and characterized at the Department for Synthesis of Materials, Jozef Stefan Institute, Ljubljana, Slovenia. TEM images of the paramagnetic nanoparticles were taken by Dr Sergey Remennik of the Hebrew University Center for Nanoscience. VSM measurements were performed by Prof. Ron Shaar at the Hebrew University Department of Earth Sciences. XPS measurements were conducted by Dr Vitaly Gutkin of the Hebrew University Center for Nanoscience. Sample cleaning was performed by Galina Chechelitsky of the Hebrew University Center for Nanoscience. Physical vapor deposition of samples was performed by Maurice Saidian of the Hebrew University Center for Nanoscience.
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