Cholesterol modulates the hydration properties of model cell membranes in a lipid dependent manner Hanna Orlikowska-Rzeznik 1 , Jan Versluis 2 , Huib J. Bakker 2 and Lukasz Piatkowski 1 1 Poznan University of Technology, Poland, 2 AMOLF, Ultrafast Spectroscopy, The Netherlands Water hydrating biological membranes is essential for maintaining cell viability and activity. Water stabilizes the structure and dynamics of the phospholipid bilayer, and mediates its interactions with other biomolecules. 1,2 Cholesterol, a fundamental lipid molecule in mammalian cells, is well-known for ordering phospholipid acyl chains and enhancing lipid packing within membranes. However, its effect on the (de)hydration properties of lipid membranes remains a topic of ongoing debate. 3,4 Recently, the computational studies revealed that cholesterol weakens the orientational preference of the water residing at the interface of a model lipid membrane. 5 This finding had never been either predicted theoretically or reported experimentally by prior studies. To address this, we employed surface-selective heterodyne-detected vibrational sum-frequency generation (HD-VSFG) spectroscopy to provide molecular-level insights into the hydration properties of zwitterionic lipid monolayers at the air/water interface with varying concentration of embedded cholesterol. We probed the interface in two spectral regions: the hydroxyl stretch to gain direct information on interfacial water and the lipid carbonyl stretch to examine the lipid perspective. Our findings demonstrate that the action of cholesterol toward the hydration properties of lipid membranes is not universal. Analysis of the HD-VSFG spectra of water revealed that cholesterol reduces the anisotropic, non- uniform orientational distribution of interfacial water molecules in the case of glycerophospholipids. However, for sphingomyelin, water orientation remains unaffected. Furthermore, we observed cholesterol-induced partial dehydration of the carbonyl region in saturated glycerophospholipid monolayer. In the presentation, I will propose the molecular mechanisms underlying the observed changes and the implications for processes occurring in the cell membrane. Acknowledgments This work has been supported by the Polish National Agency for Academic Exchange (NAWA) under the STER programme, Towards Internationalization of Poznan University of Technology Doctoral School (2022-2024). This work was co-financed from the budget funds allocated for science in the years 2019–2023 as a research project under the “Diamond Grant” program (decision: 0042/DIA/2019/48). The authors also acknowledge the financial support from the National Science Centre (Poland) 2020/37/B/ST4/01785. References 1. Chattopadhyay, E. Krok, H. Orlikowska, P. Schwille, H. G. Franquelim, L. Piatkowski, J. Am. Chem. Soc. 143 (36), 14551 (2021). 2. Laage, T. Elsaesser, J. T. Hynes, Chem. Rev. 117 (16), 10694 (2017). 3. A. Pérez, L. M. Alarcón, A. R. Verde, G. A. Appignanesi, R. E. Giménez, E. A. Disalvo, M. A. Frías, Biochim. Biophys. Acta – Biomembr. 1863 (1), 183489 (2021). 4. Cheng, C. Y., Olijve, L. L., Kausik, R., Han, S. Chem. Phys. 141 , 22D513 (2014). 5. Oh, M. I., Oh, C. I., Weaver, D. F. Phys. Chem. B 124 (18), 3686 (2020).
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