The expression plasmids were introduced into E. coli strain
BL21(DE3) (Novagen). The transformants were cultivated in LB
media containing 50 mg/ml ampicillin at 37 C. Expression and
purification of the recombinant proteins were performed by using a
MagneHis Protein Purification System (Promega). The purified
proteins were stored at 30 C in 10 mM sodium citrate buffer (pH
6.2), containing 1 mM DTT and 50% glycerol. The molar concentrations
were spectrophotometrically determined, using the values
of A280 and the extinction coefficient 41,535 M1 cm1 that was
determined using the ProtParam tool of the ExPASy server (http://
web.expasy.org) [17].