Evidence for a strong hydrogen bond in the catalytic dyad of transition-state analogue inhibitor complexes of chymotrypsin from proton-triton NMR isotope shifts.
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.
Westler
William M
WM
National Magnetic Resonance Facility at Madison, Department of Biochemistry, and Enzyme Institute, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Frey
Perry A
PA
Lin
Jing
J
Wemmer
David E
DE
Morimoto
Hiromi
H
Williams
Phillip G
PG
Markley
John L
JL
D002918:Chymotrypsin / Q000737:chemistry*; D006860:Hydrogen Bonding; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011522:Protons; D015842:Serine Proteinase Inhibitors / Q000737:chemistry*; D014316:Tritium
D011522:Protons; D015842:Serine Proteinase Inhibitors; D014316:Tritium; D002918:Chymotrypsin