3bgd
From Proteopedia
(New page: '''Unreleased structure''' The entry 3bgd is ON HOLD until Paper Publication Authors: Peng, Y., Yee, V.C. Description: Methyltransferase ''Page seeded by [http://oca.weizmann.ac.il/o...) |
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| + | {{STRUCTURE_3bgd| PDB=3bgd | SCENE= }} | ||
| - | + | '''Thiopurine S-Methyltransferase''' | |
| - | Description: Methyltransferase | ||
| + | ==Overview== | ||
| + | Thiopurine S-methyltransferase (TPMT) modulates the cytotoxic effects of thiopurine prodrugs such as 6-mercaptopurine by methylating them in a reaction using S-adenosyl- l-methionine as the donor. Patients with TPMT variant allozymes exhibit diminished levels of protein and/or enzyme activity and are at risk for thiopurine drug-induced toxicity. We have determined two crystal structures of murine TPMT, as a binary complex with the product S-adenosyl- l-homocysteine and as a ternary complex with S-adenosyl- l-homocysteine and the substrate 6-mercaptopurine, to 1.8 and 2.0 A resolution, respectively. Comparison of the structures reveals that an active site loop becomes ordered upon 6-mercaptopurine binding. The positions of the two ligands are consistent with the expected S N2 reaction mechanism. Arg147 and Arg221, the only polar amino acids near 6-mercaptopurine, are highlighted as possible participants in substrate deprotonation. To probe whether these residues are important for catalysis, point mutants were prepared in the human enzyme. Substitution of Arg152 (Arg147 in murine TPMT) with glutamic acid decreases V max and increases K m for 6-mercaptopurine but not K m for S-adenosyl- l-methionine. Substitution at this position with alanine or histidine and similar substitutions of Arg226 (Arg221 in murine TPMT) result in no effect on enzyme activity. The double mutant Arg152Ala/Arg226Ala exhibits a decreased V max and increased K m for 6-mercaptopurine. These observations suggest that either Arg152 or Arg226 may participate in some fashion in the TPMT reaction, with one residue compensating when the other is altered, and that Arg152 may interact with substrate more directly than Arg226, consistent with observations in the murine TPMT crystal structure. | ||
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Wed Jun 11 | + | ==About this Structure== |
| + | 3BGD is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Mus_musculus Mus musculus]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=3BGD OCA]. | ||
| + | |||
| + | ==Reference== | ||
| + | Structural basis of substrate recognition in thiopurine s-methyltransferase., Peng Y, Feng Q, Wilk D, Adjei AA, Salavaggione OE, Weinshilboum RM, Yee VC, Biochemistry. 2008 Jun 10;47(23):6216-25. Epub 2008 May 17. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/18484748 18484748] | ||
| + | [[Category: Mus musculus]] | ||
| + | [[Category: Single protein]] | ||
| + | [[Category: Thiopurine S-methyltransferase]] | ||
| + | [[Category: Peng, Y.]] | ||
| + | [[Category: Yee, V C.]] | ||
| + | [[Category: Cytoplasm]] | ||
| + | [[Category: Methyltransferase]] | ||
| + | [[Category: S-adenosyl-l-methionine]] | ||
| + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Wed Jun 11 10:47:05 2008'' | ||
Revision as of 07:47, 11 June 2008
Thiopurine S-Methyltransferase
Overview
Thiopurine S-methyltransferase (TPMT) modulates the cytotoxic effects of thiopurine prodrugs such as 6-mercaptopurine by methylating them in a reaction using S-adenosyl- l-methionine as the donor. Patients with TPMT variant allozymes exhibit diminished levels of protein and/or enzyme activity and are at risk for thiopurine drug-induced toxicity. We have determined two crystal structures of murine TPMT, as a binary complex with the product S-adenosyl- l-homocysteine and as a ternary complex with S-adenosyl- l-homocysteine and the substrate 6-mercaptopurine, to 1.8 and 2.0 A resolution, respectively. Comparison of the structures reveals that an active site loop becomes ordered upon 6-mercaptopurine binding. The positions of the two ligands are consistent with the expected S N2 reaction mechanism. Arg147 and Arg221, the only polar amino acids near 6-mercaptopurine, are highlighted as possible participants in substrate deprotonation. To probe whether these residues are important for catalysis, point mutants were prepared in the human enzyme. Substitution of Arg152 (Arg147 in murine TPMT) with glutamic acid decreases V max and increases K m for 6-mercaptopurine but not K m for S-adenosyl- l-methionine. Substitution at this position with alanine or histidine and similar substitutions of Arg226 (Arg221 in murine TPMT) result in no effect on enzyme activity. The double mutant Arg152Ala/Arg226Ala exhibits a decreased V max and increased K m for 6-mercaptopurine. These observations suggest that either Arg152 or Arg226 may participate in some fashion in the TPMT reaction, with one residue compensating when the other is altered, and that Arg152 may interact with substrate more directly than Arg226, consistent with observations in the murine TPMT crystal structure.
About this Structure
3BGD is a Single protein structure of sequence from Mus musculus. Full crystallographic information is available from OCA.
Reference
Structural basis of substrate recognition in thiopurine s-methyltransferase., Peng Y, Feng Q, Wilk D, Adjei AA, Salavaggione OE, Weinshilboum RM, Yee VC, Biochemistry. 2008 Jun 10;47(23):6216-25. Epub 2008 May 17. PMID:18484748 Page seeded by OCA on Wed Jun 11 10:47:05 2008
