1g4e
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(New page: 200px<br /><applet load="1g4e" size="450" color="white" frame="true" align="right" spinBox="true" caption="1g4e, resolution 1.60Å" /> '''THIAMIN PHOSPHATE SY...)
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Revision as of 13:34, 20 November 2007
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THIAMIN PHOSPHATE SYNTHASE
Overview
Thiamin phosphate synthase catalyzes the formation of thiamin phosphate, from 4-amino-5-(hydroxymethyl)-2-methylpyrimidine pyrophosphate and, 5-(hydroxyethyl)-4-methylthiazole phosphate. Several lines of evidence, suggest that the reaction proceeds via a dissociative mechanism. The, previously determined crystal structure of thiamin phosphate synthase in, complex with the reaction products, thiamin phosphate and magnesium, pyrophosphate, provided a view of the active site and suggested a number, of additional experiments. We report here seven new crystal structures, primarily involving crystals of S130A thiamin phosphate synthase soaked in, solutions containing substrates or products. We prepared S130A thiamin, phosphate synthase with the intent of characterizing the enzyme-substrate, complex. Surprisingly, in three thiamin phosphate synthase structures, the, active site density cannot be modeled as either substrates or products., For these structures, the best fit to the electron density is provided by, a model that consists of independent pyrimidine, pyrophosphate, and, thiazole phosphate fragments, consistent with a carbenium ion, intermediate. The resulting carbenium ion is likely to be further, stabilized by proton transfer from the pyrimidine amino group to the, pyrophosphate to give the pyrimidine iminemethide, which we believe is the, species that is observed in the crystal structures.
About this Structure
1G4E is a Single protein structure of sequence from Bacillus subtilis. Active as Thiamine-phosphate diphosphorylase, with EC number 2.5.1.3 Full crystallographic information is available from OCA.
Reference
Structural characterization of the enzyme-substrate, enzyme-intermediate, and enzyme-product complexes of thiamin phosphate synthase., Peapus DH, Chiu HJ, Campobasso N, Reddick JJ, Begley TP, Ealick SE, Biochemistry. 2001 Aug 28;40(34):10103-14. PMID:11513589
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