title: Probing Hydronium Ion Histidine NH Exchange Rate Constants in the M2 Channel via Indirect Observation of Dipolar-Dephased15N Signals in Magic-Angle-Spinning NMR.
abstract: Water-protein chemical exchange in membrane-bound proteins is an important parameter for understanding how proteins interact with their aqueous environment, but has been difficult to observe in membrane-bound biological systems. Here, we demonstrate the feasibility of probing specific water-protein chemical exchange in membrane-bound proteins in solid-state MAS NMR. By spin-locking the1H magnetization along the magic angle, the1H spin diffusion is suppressed such that a water-protein chemical exchange process can be monitored indirectly by dipolar-dephased15N signals through polarization transfer from1H. In the example of the Influenza A full length M2 protein, the buildup of dipolar-dephased15N signals from the tetrad of His37 side chains have been observed as a function of spin-lock time. This confirms that hydronium ions are in exchange with protons in the His37 NH bonds at the heart of the M2 proton conduction mechanism, with an exchange rate constant of ∼1750 s-1for pH 6.2 at -10 °C.
authors.affiliation: National High Magnet Field Lab , 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States.
authors.forename: Riqiang
authors.initials: R
authors.lastname: Fu
authors.affiliation: Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States.
authors.forename: Yimin
authors.initials: Y
authors.lastname: Miao
authors.affiliation: Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States.
authors.forename: Huajun
authors.initials: H
authors.lastname: Qin
authors.affiliation: National High Magnet Field Lab , 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States.|Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306, United States.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Cross
mesh_terms: D006639:Histidine / Q000737:chemistry*; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular; D009861:Onium Compounds / Q000737:chemistry*; D011522:Protons; D014763:Viral Matrix Proteins / Q000737:chemistry*; D000086082:Viroporin Proteins
chemical_list: D006639:Histidine; D009587:Nitrogen Isotopes; D009861:Onium Compounds; D011522:Protons; D014763:Viral Matrix Proteins; C488937:M2 protein, Influenza A virus; D000086082:Viroporin Proteins; C027727:hydronium ion