Protein Engineering, Vol. 14, No. 5, 379-386,
May 2001
© 2001 Oxford University Press
New secretory strategies for Kluyveromyces lactis ß-galactosidase
Departamento de Bioloxía Celular e Molecular, Facultade de Ciencias, Campus da Zapateira s/n, 15071-A Coruña, Spain
We examined several strategies for the secretion of Kluyveromyces lactis ß-galactosidase into the culture medium, in order to facilitate the downstream processing and purification of this intracellular enzyme of great industrial interest. We constructed plasmids by fusing the LAC4 gene or engineered variants to the secretion signal of the K.lactis killer toxin or to the secretion signal of the Saccharomyces cerevisiae 
-factor. With these plasmids we transformed strains of the yeasts K.lactis and S.cerevisiae, respectively and tested ß-galactosidase extracellular activity in different culture media. We achieved partial secretion of ß-galactosidase in the culture medium since the high molecular weight and oligomeric nature of the enzyme, among other factors, preclude full secretion. The percentage of secretion was improved by directed mutagenesis of the N-terminus of the protein. We developed several deletion mutants which helped us to propose structure–function relationships by comparison with the available data on the homologous Escherichia coli ß-galactosidase. The influence of the culture conditions on heterologous ß-galactosidase secretion was also studied.