NMR studies of the alpha-chymotrypsin-(R)-1-acetamido-2-(4- fluorophenyl)ethane-1-boronic acid complex.
The interaction of (R)-1-acetamido-2-(4-fluorophenyl)ethane-1-boronic acid with alpha-chymotrypsin at pH 4 was studied by a variety of 19F-NMR experiments. It was demonstrated that this compound forms a complex with a 1:1 stoichiometry, probably because the boronic acid acts as a 'transition state' inhibitor of the enzyme. Analysis of fluorine T1 relaxation behavior and 19F[1H] NOE data shows that the rate constant for dissociation of the complex is 1.3 s-1 and that the motion of the 4-fluoroaromatic ring within the complex can be characterized by an overall rotational correlation time of 13 ns and a correlation time for rotation about its local C2 axis of 110 ns. Enzyme-induced fluorine chemical shifts, fluorine relaxation times, line width data and 2D 19F[1H] NOE results suggest that the structure of the complex in the vicinity of the fluoroaromatic ring is similar to that found in a closely similar acylated enzyme. However, the dynamics of 4-fluoroaromatic ring motions are different in the two systems, with the ring being slightly more mobile in the boronic acid complex than in the acylenzyme.
Department of Chemistry, University of California, Santa Barbara 93106.
L A
LA
Sylvia
J T
JT
Gerig
D001665:Binding Sites; D001897:Boronic Acids / Q000737:chemistry*; D002918:Chymotrypsin / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D005461:Fluorine / Q000737:chemistry; D005464:Fluorobenzenes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D009038:Motion; D013997:Time Factors
D001897:Boronic Acids; D005464:Fluorobenzenes; C081609:1-acetamido-2-(4-fluorophenyl)ethane-1-boronic acid; D005461:Fluorine; D002918:Chymotrypsin