title: Evidence for a strong hydrogen bond in the catalytic dyad of transition-state analogue inhibitor complexes of chymotrypsin from proton-triton NMR isotope shifts.
abstract: We present here the first accurate measurements of 1H (H) versus 3H (T) isotope shift (DeltadeltaT-H = deltaT - deltaH) in a protein. This approach was used to investigate the strength of the hydrogen bond between His57 and Asp102 in the catalytic dyad of chymotrypsin in three transition-state analogue inhibited complexes: N-acetyl-l-phenylalanyl trifluoromethyl ketone (N-AcF-CF3), N-acetyl-l-valyl-l-phenylalanyl trifluoromethyl ketone (N-AcVF-CF3), and N-acetyl-l-leucyl-l--phenylalanyl trifluoromethyl ketone (N-AcLF-CF3). The measured DeltadeltaT-H values for His57 Hdelta1 in these complexes were between -0.63 and -0.68 ppm. These values are consistent with a strong hydrogen bond in each of these complexes, but not with a very strong hydrogen bond, which would be expected to have a DeltadeltaT-H. value near or greater than zero.
authors.affiliation: National Magnetic Resonance Facility at Madison, Department of Biochemistry, and Enzyme Institute, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Westler
authors.forename: Perry A
authors.initials: PA
authors.lastname: Frey
authors.forename: Jing
authors.initials: J
authors.lastname: Lin
authors.forename: David E
authors.initials: DE
authors.lastname: Wemmer
authors.forename: Hiromi
authors.initials: H
authors.lastname: Morimoto
authors.forename: Phillip G
authors.initials: PG
authors.lastname: Williams
authors.forename: John L
authors.initials: JL
authors.lastname: Markley
mesh_terms: D002918:Chymotrypsin / Q000737:chemistry*; D006860:Hydrogen Bonding; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011522:Protons; D015842:Serine Proteinase Inhibitors / Q000737:chemistry*; D014316:Tritium
chemical_list: D011522:Protons; D015842:Serine Proteinase Inhibitors; D014316:Tritium; D002918:Chymotrypsin