Expression and purification of a soluble ESX-binding core domain of SUR2

For HER2 overexpression, the ESX transcription factor must interact with both the HER2 promoter and Sur2, a subunit of human mediator complex, using its Ets domain and transactivation domain, respectively. HER2 overexpression is a marker of poor prognosis in various types of cancers. Thus, interfering with the ESX-Sur2 interaction has been suggested as a novel strategy for the treatment of HER2 positive cancers. To design small molecule inhibitors against the ESX-Sur2 interaction, it is necessary to identify the structure of the interface of ESX-Sur2 binding. Therefore, in this study, we determined the optimal conditions for the overexpression and purification of a new version of Sur2, Sur2391-582, which was able to bind to ESX. To stabilize (His)6-Sur2391-582, various different buffered conditions over a wide range of pH and ionic strengths were examined. The molecular mass of (His)6-Sur2391-582 was determined using mass spectroscopy and size exclusion chromatography. The purified (His)6-Sur2391-582 protein displayed the same biological properties as that of the Sur2 full-length protein.