| Autor: |
Zhang R; National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States.; Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32301, United States., Cross TA; National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States.; Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32301, United States., Peng X; CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China., Fu R; National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States. |
| Abstrakt: |
Understanding water dynamics and structure is an important topic in biological systems. It is generally held in the literature that the interfacial water of hydrated phospholipids is highly mobile, in fast exchange with the bulk water ranging from the nano- to femtosecond timescale. Although nuclear magnetic resonance (NMR) is a powerful tool for structural and dynamic studies, direct probing of interfacial water in hydrated phospholipids is formidably challenging due to the extreme population difference between bulk and interfacial water. We developed a novel 17 O solid-state NMR technique in combination with an ultra-high-field magnet (35.2 T) to directly probe the functionally important interfacial water. By selectively suppressing the dominant bulk water signal, we observed two distinct water species in the headgroup region of hydrated dimyristoylphosphatidylcholine (DMPC) lipid bilayers for the first time. One water species denoted as "confined water" is chemically and dynamically different from the bulk water (∼0.17 ppm downfield and a slightly shorter spin-lattice relaxation time). Another water species denoted as "bound water" has severely restricted motion and a distinct chemical shift (∼12 ppm upfield). Additionally, the bulk water is not as "free" as pure water, resulting from the fast exchange with the water molecules that weakly and transiently interact with the lipid choline groups. These new discoveries clearly indicate the existence of the interfacial water molecules that are relatively stable over the NMR timescale (on the order of milliseconds), providing an opportunity to characterize water dynamics on the millisecond or slower timescale in biomacromolecules. |
