A SBgl3 gene without the signal peptide was expressed in
P. pastoris to determine the structural elements involved in the catalytic site of SBgl3. The purification of rSBgl3 was facilitated by
fusion of (His)6 at the C-terminus. The SBgl3 gene fused with and
without (His)6 at its C-terminus was successfully cloned into pPICZaA,
and designated pPICZaA/SBgl3His and pPICZaA/SBgl3, respectively.
P. pastoris harboring pPICZaA/SBgl3 produced SBgl3 with the same
level of activity as that harboring pPICZaA/SBgl3His (Supplementary
Fig. 2). These results suggested that the polyhistidine (His)6 tag did
not affect SBgl3 activity. The rSBgl3 fused with the polyhistidine
(His)6 tag (rSBgl3His) was, therefore, expressed for purification
and characterization. After adjusting the optimal conditions for
expression, rSBgl3His produced by P. pastoris cultured in BMMY
at 16 C was detected at 0.5 nkat/ml using 1 mM torvoside A(1).