Standardized lab-scale production of the recombinant fusion protein HUG for the nanoscale analysis of bilirubin

The recombinant bifunctional protein HELP-UnaG (HUG) is a fusion product of the Human Elastin-like Polypeptide (HELP) with the bilirubin-binding fluorescent protein UnaG. HUG is used for the fluorometric detection of bilirubin in serum and a variety of biological fluids and extracts. Here we describe a detailed method for the standardized production and purification of HUG from <i>E. coli</i> extracts on a laboratory scale. This method takes advantage of the HELP-specific thermoreactive behavior that enables the separation of HUG from complex <i>E. coli</i> extracts by repeated precipitation/re-dissolution steps at near physiological temperature.•The method is based on the inverse thermal transition process.•The "green" method is affordable for basic laboratories and can be easily transferred to new users.