To compare aptamer-based downstream processing directly
with conventional IMAC, we have purified BSTE-His and
PFEI-His from crude E. coli lysates utilizing 6H5- and 6H7-
modified magnetic beads as well as Co2þ-loaded membrane
adsorbers. The eluates of the different purification processes
were analyzed by SDS–PAGE (Fig. 6). Both proteins
could be successfully purified with 6H5-and 6H7-modified
magnetic beads and IMAC. The purity of the his-tagged
proteins was determined by densitometry. For PFEI-His a
purity of 84% for the purification via 6H5-modified
magnetic beads and 80% for the purification via 6H7-
modified magnetic beads was calculated. These values are
comparable to the purity determined for IMAC (77%). In
case of BSTE-His, the aptamer-based downstream proces-
sing resulted in purities of 58% for 6H5-modified beads and
77% for 6H7-modified beads, while IMAC resulted in 85%
purity. In summary, we were able to purify PFEI-His and
BSTE-His via 6H7- and 6H5 modified magnetic beads with
purification efficiencies in the same range determined for
IMAC.