Dl. Wilkinson et al., PURIFICATION BY IMMOBILIZED METAL AFFINITY-CHROMATOGRAPHY OF HUMAN ATRIAL-NATRIURETIC-PEPTIDE EXPRESSED IN A NOVEL THIOREDOXIN FUSION PROTEIN, Biotechnology progress, 11(3), 1995, pp. 265-269
A fusion protein that contains human atrial natriuretic peptide (ANP)
at its carboxy terminus has been genetically engineered with the objec
tive of being able to produce the peptide in a process with a relative
ly simple purification procedure. The fusion protein also includes a (
His)(6) metal affinity binding site at the amino terminus, followed by
Escherichia coli thioredoxin, a factor X(a) protease recognition site
, and ANP. With induction of the tac promoter at 30 degrees C, the exp
ression level of the fusion protein was high (10% of total cell protei
n as measured by densitometry) and it was almost completely (92%) expr
essed as a soluble protein in the cytoplasm. A step gradient elution w
ith imidazole of a column of Ni2+ chelated to iminodiacetic acid-agaro
se saturated with proteins in crude cell extract gave a very nearly pu
re fusion protein. After digestion of the purified fusion protein with
factor X(a) protease, ANP of exactly the correct size (to within 2 Da
) was observed by coupled HPLC/mass spectrometry.