Straightforward isolation of phosphatidyl-ethanolamine-binding protein-1 (PEBP-1) and ubiquitin from bovine testis by hydrophobic-interaction chromatography (HIC)

Isolation of phosphatidyl-ethanolamine-binding protein-1 (PEBP-1) from bovine brain was described almost three decades ago but it required a large number of steps to reach high purity. After the fractionation of bovine testis proteins by ammonium sulfate precipitation we found that PEBP-1, detected by Western blotting, was among the very few proteins still soluble at 80% ammonium sulfate saturation (3.2 M). This soluble fraction (S80) was directly loaded onto a phenyl sepharose column equilibrated at the same ammonium sulfate concentration (3.2 M). A stepwise elution of the retained material at 1.0, 0.5, 0.2, 0.1 M ammonium sulfate in ammonium hydrogen carbonate was performed and then with ammonium hydrogen carbonate alone and finally with 50% ethylene glycol. All fractions were analyzed by SDS–PAGE and Western blotting and the fractions containing PEBP-1 was further fractionated by size exclusion chromatography on a HR75 Superdex column permitting the isolation of ubiquitin in addition to PEBP-1 as demonstrated by Western blotting and mass spectrometry. This study shows the feasibility of hydrophobic interaction chromatography (HIC) on phenyl sepharose at a very high ammonium sulfate concentration (3.2 M; 80% saturation) to efficiently purify the proteins that are still soluble in these extreme conditions.