Expression of the alpha-galactosidase from Cyamopsis tetragonoloba (guar) by Hansenula polymorpha

The methylotrophic yeast Hansenula polymorpha, a host organism for the production of heterologous proteins, has been applied to produce the alpha-galactosidase from the plant Cyamopsis tetragonoloba (guar). The yeast/Escherichia coli shuttle expression vector used is based on the origin of replication of the endogenous 2 microns plasmid of Saccharomyces cerevisiae and the LEU2 gene of S. cerevisiae for selection in H. polymorpha. In the expression vector, the alpha-galactosidase is controlled by the methanol-regulated promoter from the methanol oxidase gene, MOX, of H. polymorpha. The signal sequence of SUC2 (invertase) from the yeast S. cerevisiae, was used to ensure secretion of the alpha-galactosidase enzyme. After transformation and stabilization, the expression vector was stably integrated in the genome. The active alpha-galactosidase enzyme was efficiently secreted (greater than 85%) and after methanol induction, the expression level was 42 mg/l. Amino-terminal sequencing of the purified alpha-galactosidase enzyme synthesized by H. polymorpha showed that the S. cerevisiae invertase signal sequence was correctly processed by H. polymorpha. The secreted alpha-galactosidase was glycosylated and had a sugar content of 9.5%. The specific activity of the alpha-galactosidase produced by H. polymorpha was 38 U mg-1 compared to 100 U mg-1 for the guar alpha-galactosidase. Deglycosylation of the H. polymorpha alpha-galactosidase restored the specific activity completely.