Different mechanisms behind low enzyme activity in vivo of two different variants of Thiopurine S-methyltransferase, TPMT
2010 (English)In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 277, no Suppl. 1, 257-258 p.Article in journal, Meeting abstract (Other academic) Published
In treatment of acute lymphoblastic leukemia and inflammatorybowel disease (IBD) thiopurines such as azathioprine and 6-mercaptopurineare used. All of these drugs are prodrugs and are, inthe cell, converted to 6-thioguanines (6-TGNs) and incorporatedinto DNA or inhibiting purine synthesis. A key enzyme for thisregulation is the cytosolic enzyme thiopurine S-methyltransferase(TPMT). This enzyme degrades azathioprine and 6-mercaptopurineto methylmercapto-purine and thereby reduces the bioavailabilityof the 6-TGNs incorporated into DNA. TPMT is apolymorphic enzyme with at least 29 different allelic variantsknown today and is one of the more classical examples of pharmacogeneticswhere the TPMT enzyme activity of the allelic variantsis directly correlated to the clinical dosages of the thiopurines, with a 10–15 fold dosage reduction for an allelic variantwith low TPMT enzyme activity. Even though TPMT is awell studied protein. Many studies have been performed in yeast‘‘suspensions’’ and not on pure protein solutions. It has beenspeculated and in a few cases shown that the reason for the lowactivity for most of the allelic variants is mainly due to the lowstability and/or tendency to aggregate. The mutations in thisstudy TPMT *2 (A80P) and TPMT * 5 (L49S) are both situatedat a distance far from the active site, however the enzyme activitiesare severely affected at 37°C. Preliminary results, using a repertoireof techniques such as CD, fluorescence and limitedproteolysis experiments suggest two different mechanisms for thelow enzyme activity at a temperature corresponding to in vivo conditions.
Place, publisher, year, edition, pages
Wiley-Blackwell, 2010. Vol. 277, no Suppl. 1, 257-258 p.
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:liu:diva-58962ISI: 000278565100897OAI: oai:DiVA.org:liu-58962DiVA: diva2:347777
35th Congress of the Federation-of-European-Biochemical-Societies, Gothenburg, Sweden, June 26-July 01, 2010