Background

SUMO is short for Small Ubiquitin-like Modifier, the 100 amino acid sequence, which is necessary for regulation of protein transport and is important for controlling transcription for eukaryotic cells. Recombinant proteins expressed in E. coli may fail to fold properly, instead forming aggregates and precipitating as inclusion bodies. This insolubility may be due to the presence of codons read inefficiently by E. coli, differences in eukaryotic and prokaryotic ribosomes, or lack of appropriate molecular chaperones for proper protein folding. In order to purify such proteins it may be necessary to fuse the protein of interest with a solubility tag such as SUMO or MBP (maltose-binding protein) to increase the protein's solubility. SUMO can later be cleaved from the protein of interest using a SUMO-specific protease such as Ulp1 peptidase.