2D 1H-31P Solid-State NMR Studies of the Dependence of Inter-Bilayer Water Dynamics on Lipid Headgroup Structure and Membrane Peptides

摘要

The dynamics of hydration water in several phospholipid membranes of different compositions is studied by 2D ¹H-³¹P heteronuclear correlation NMR under magic-angle spinning. By using a ¹H T2 filter and ¹H mixing time before and after the evolution period, inter-bilayer water is selectively detected without resonance overlap from bulk water outside the multilamellar vesicles. Moreover the ¹H T2 relaxation time of the inter-bilayer water is measured. Lipid membranes with labile protons either in the lipid headgroup or in sterols exhibit water-³¹P correlation peaks while membranes free of exchangeable protons do not, indicating that the mechanism for water-lipid correlation is chemical exchange followed by relayed magnetization transfer to ³¹P. In the absence of membrane proteins, the inter-bilayer water ¹H T2’s are several tens of milliseconds. Incorporation of charged membrane peptides shortened this inter-bilayer water T2 significantly. This T2 reduction is attributed to the peptides’ exchangeable protons, molecular motion and intermolecular hydrogen bonding, which affect the water dynamics and the chemically relayed magnetization transfer process.