Electrophilic catalysis by histidine-95 in triosephosphate isomerase has been probed by using Fourier transform infrared spectroscopy and X-ray crystallography. The carbonyl stretching frequency of dihydroxyacetone phosphate bound to the wild-type enzyme is known to be 19 cm-1 lower (at 1713 cm-1) than that of dihydroxyacetone phosphate free in solution (at 1732 cm-1), and this decrease in stretching frequency has been ascribed to an enzymic electrophile that polarizes the substrate carbonyl group toward the transition state for the enolization ...
Electrophilic catalysis by histidine-95 in triosephosphate isomerase has been probed by using Fourier transform infrared spectroscopy and X-ray crystallography. The carbonyl stretching frequency of dihydroxyacetone phosphate bound to the wild-type enzyme is known to be 19 cm-1 lower (at 1713 cm-1) than that of dihydroxyacetone phosphate free in solution (at 1732 cm-1), and this decrease in stretching frequency has been ascribed to an enzymic electrophile that polarizes the substrate carbonyl group toward the transition state for the enolization. Infrared spectra of substrate bound to two site-directed mutants of yeast triosephosphate isomerase in which histidine-95 has been changed to glutamine or to asparagine show unperturbed carbonyl stretching frequencies between 1732 and 1742 cm-1. The lack of carbonyl polarization when histidine-95 is removed suggests that histidine-95 is indeed the catalytic electrophile, at least for dihydroxyacetone phosphate. Kinetic studies of the glutamine mutant (H95Q) have shown that the enzyme follows a subtly different mechanism of proton transfers involving only a single acid-base catalytic group. These findings suggest an additional role for histidine-95 as a general acid-base catalyst in the wild-type enzyme. The X-ray crystal structure of the H95Q mutant with an intermediate analogue, phosphoglycolohydroxamate, bound at the active site has been solved to 2.8-A resolution, and this structure clearly implicates glutamate-165, the catalytic base in the wild-type isomerase, as the sole acid-base catalyst for the mutant enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
Related Citations:
Crystallographic Analysis of the Complex between Triosephosphate Isomerase and 2-Phosphoglycolate at 2.5-Angstroms Resolution. Implications for Catalysis Lolis, E., Petsko, G.A. (1990) Biochemistry 29: 6619
Structure of Yeast Triosephosphate Isomerase at 1.9-Angstroms Resolution Lolis, E., Alber, T., Davenport, R.C., Rose, D., Hartman, F.C., Petsko, G.A. (1990) Biochemistry 29: 6609
Crystallography and Site-Directed Mutagenesis of Yeast Triosephosphate Isomerase. What Can We Learn About Catalysis from a "Simple" Enzyme? Alber, T.C., Davenportjunior, R.C., Giammona, D.A., Lolis, E., Petsko, G.A., Ringe, D. (1987) Cold Spring Harb Symp Quant Biol 52: 603
Crystallization of Yeast Triose Phosphate Isomerase from Polyethylene Glycol. Protein Crystal Formation Following Phase Separation Alber, T., Hartman, F.C., Johnson, R.M., Petsko, G.A., Tsernoglou, D. (1981) J Biol Chem 256: 1356
On the Three-Dimensional Structure and Catalytic Mechanism of Triose Phosphate Isomerase Alber, T., Banner, D.W., Bloomer, A.C., Petsko, G.A., Phillips, D., Rivers, P.S., Wilson, I.A. (1981) Philos Trans R Soc London,ser B 293: 159
Organizational Affiliation:
Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138.
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