Background: Human alpha 1-antitrypsin (AAT) is a potent inhibitor of
multiple serine proteases, and protects tissues against their harmful
effects. Individuals with reduced or abnormal production of this
inhibitor need intravenous administration of exogenous protein. In this
study, we employed the methylotrophic (methanol utilizing) yeast Pichia
pastoris (P. pastoris) as a preferential host for efficient
production and secretion of recombinant AAT. Furthermore, we examined
different strategies to maximize the yield of the secreted protein.
Results: Our findings revealed that optimizing the codon usage of AAT
gene for P. pastoris had positive effects on the level of secreted AAT
under the control of inducible alcohol oxidase 1 (AOX1) and
constitutive glycerol aldehyde phosphate dehydrogenase (GAP) promoters.
Compared to AOX1, the GAP promoter increased the yield of AAT by more
than two fold. It was also demonstrated that the human AAT native
signal sequence was more effective than the well-known yeast signal
sequence, alpha mating factor (\u3b1-MF). Doubling gene dosage nearly
doubled the production of AAT, though dosages exceeding this limit had
negative effects on the yield. Conclusion: P. pastoris is shown to be
an efficient expression system for production of recombinant and
biologically active AAT. Also different strategies could be used to
elevate the amount of this secretable protein