Grazing-Angle Neutron Diffraction Study of the Water Distribution in Membrane Hemifusion: From the Lamellar to Rhombohedral Phase

Journal Article · 20 September 2018 · Journal of Physical Chemistry Letters

DOI: https://doi.org/10.1021/acs.jpclett.8b01602 · OSTI ID:1471910

Qian, Shuo  ^[1]; Rai, Durgesh K. ^[2]

---

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division, and Center for Structural Molecular Biology
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division

The water distribution between lipid bilayers is important in understanding the role of the hydration force at different steps of the membrane fusion pathway. Here in this study, we used grazing-angle neutron diffraction to map out the water distribution in lipid bilayers transiting from a lamellar structure to the hemifusion “stalk” structure in a rhombohedral phase. Under osmotic pressure exerted by different levels of relative humidity, the lipid membrane sample was maintained in equilibrium at different lattices suitable for neutron diffraction. The D₂O used to hydrate the lipid membrane sample stood out from the lipid in the reconstructed structure because of its much higher coherent neutron scattering length density. The density map indicates that water dissociated from the headgroup in the lamellar phase. In the rhombohedral phase, water was significantly reduced and was squeezed into pockets around the stalk. This study complements earlier structural studies by grazing-angle X-ray diffraction, which is sensitive to only the parts of the structure with high electron density (such as phosphors). The experiment also demonstrated that the recently developed time-of-flight small-angle neutron scattering beamline at the Spallation Neutron Source is suitable for grazing-angle neutron diffraction to provide the structures of large unit cells on the order of a few nanometers, such as biomembrane structures.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1471910
• Journal Information: Journal of Physical Chemistry Letters, Vol. 9; ISSN 1948-7185
• Publisher: American Chemical SocietyCopyright Statement
• Country of Publication: United States
• Language: English