Cloning, expression, purification and crystallization of NHR3 domain from acute myelogenous leukemia-related protein AML1-ETO.

The t(8;21) translocation is one of the most frequent chromosome abnormalities in acute myeloid leukemia. This translocation creates a fusion between the acute myelogenous leukemia 1 (AML1, a transcription factor) gene on chromosome 21 and the eight-twenty-one (ETO, a zinc finger nuclear protein) gene on chromosome 8, leading to the repression of certain AML1 target genes. We cloned NHR3 domain coding fragment into vector pGEX-6p-1 using PCR and obtained recombinant plasmid pGEX-6p-1-NHR3, which can be induced to stably overexpress fusion protein in E. coli. Through the purification on GST affinity chromatography column and PreScission protease cleavage, a large amount of NHR3 protein with high purity was obtained. In order to avoid possible interference of some strong negative charged molecules, NHR3 protein was further purified by Mono Q anion exchange chromatography. The NHR3 crystals were grown with hanging drop/vapor diffusion method and the first crystals appeared after four weeks at 18 degrees in 0.2 M Tris-sodium citrate dihydrate, 0.1 M sodium cacodylate, pH 6.5, and 30% iso-propanol (V/V). ESI mass spectrum showed that the molecular weight of this domain was in agreement with its primary structure sequence prediction, and circular dichroism spectral data (190-250 nm) showed that NHR3 had a well-defined secondary structure of 25.9% alpha-helix, 23.2% random coil and 50.9% turn, which was consistent with GOV4 software prediction.