期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2020
卷号：117
期号：22
页码：11908-11915
DOI：10.1073/pnas.2001083117
出版社：The National Academy of Sciences of the United States of America
摘要：Water wires are critical for the functioning of many membrane proteins, as in channels that conduct water, protons, and other ions. Here, in liquid crystalline lipid bilayers under symmetric environmental conditions, the selective hydrogen bonding interactions between eight waters comprising a water wire and a subset of 26 carbonyl oxygens lining the antiparallel dimeric gramicidin A channel are characterized by 17 O NMR spectroscopy at 35.2 T (or 1,500 MHz for 1 H) and computational studies. While backbone 15 N spectra clearly indicate structural symmetry between the two subunits, single site 17 O labels of the pore-lining carbonyls report two resonances, implying a break in dimer symmetry caused by the selective interactions with the water wire. The 17 O shifts document selective water hydrogen bonding with carbonyl oxygens that are stable on the millisecond timescale. Such interactions are supported by density functional theory calculations on snapshots taken from molecular dynamics simulations. Water hydrogen bonding in the pore is restricted to just three simultaneous interactions, unlike bulk water environs. The stability of the water wire orientation and its electric dipole leads to opposite charge-dipole interactions for K ions bound at the two ends of the pore, thereby providing a simple explanation for an ∼20-fold difference in K affinity between two binding sites that are ∼24 Å apart. The 17 O NMR spectroscopy reported here represents a breakthrough in high field NMR technology that will have applications throughout molecular biophysics, because of the acute sensitivity of the 17 O nucleus to its chemical environment.
关键词：molecular dynamics ; gramicidin A ; ultra-high field NMR ; water wire ; 17 O NMR
