title: Fourier transform ion cyclotron resonance MS reveals the presence of a water molecule in an enzyme transition-state analogue complex.
abstract: The structures of several powerful inhibitors of hydrolytic enzymes resemble that of the altered substrate in the transition state, except that a hydrogen atom replaces one substituent (typically the leaving group). To test the hypothesis that a water molecule might be present in the gap resulting from this replacement, we examined a transition-state analogue complex formed by Escherichia coli cytidine deaminase by Fourier transform ion cyclotron resonance MS in electrospray mode. Upon nebularization from aqueous solution under conditions (pH 5.6) where the enzyme is active, cytidine deaminase remains dimeric in the vapor phase. In the presence of inhibitor, the enzyme's exact mass can be used to infer the presence at each active site of zinc, 5-fluoro-3,4-dihydrouridine, and a single water molecule.
authors.affiliation: Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA.
authors.forename: Christoph H
authors.initials: CH
authors.lastname: Borchers
authors.forename: Victor E
authors.initials: VE
authors.lastname: Marquez
authors.forename: Gottfried K
authors.initials: GK
authors.lastname: Schroeder
authors.forename: Steven A
authors.initials: SA
authors.lastname: Short
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Snider
authors.forename: J Paul
authors.initials: JP
authors.lastname: Speir
authors.forename: Richard
authors.initials: R
authors.lastname: Wolfenden
mesh_terms: D017357:Cyclotrons; D003564:Cytidine Deaminase / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology; D005583:Fourier Analysis; D006863:Hydrogen-Ion Concentration; D011994:Recombinant Proteins / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014867:Water / Q000032:analysis*
chemical_list: D011994:Recombinant Proteins; D014867:Water; D003564:Cytidine Deaminase