3ypi
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(New page: 200px<br /><applet load="3ypi" size="450" color="white" frame="true" align="right" spinBox="true" caption="3ypi, resolution 2.8Å" /> '''ELECTROPHILIC CATALYS...)
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Revision as of 17:54, 20 November 2007
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ELECTROPHILIC CATALYSIS IN TRIOSEPHOSPHASE ISOMERASE: THE ROLE OF HISTIDINE-95
Overview
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)
About this Structure
3YPI is a Single protein structure of sequence from Saccharomyces cerevisiae with PGH as ligand. Active as Triose-phosphate isomerase, with EC number 5.3.1.1 Full crystallographic information is available from OCA.
Reference
Electrophilic catalysis in triosephosphate isomerase: the role of histidine-95., Komives EA, Chang LC, Lolis E, Tilton RF, Petsko GA, Knowles JR, Biochemistry. 1991 Mar 26;30(12):3011-9. PMID:2007138
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