Cytoplasmic expression of a thermostable invertase from Thermotoga maritima in Lactococcus lactis

Objectives To evaluate the secretory and cytoplasmic expression of a thermostable Thermogata maritima invertase in Lactococcus lactis . Results The thermostable invertase from T. maritima was cloned with and without the USP45 secretory peptide into the pNZ8148 vector for nisin-inducible expression in L. lactis . The introduction of an USP45 secretion peptide at the N -terminal of the enzyme led to a loss of protein solubility. Computational homology modeling and hydrophobicity studies indicated that the USP45 peptide exposes a stretch of hydrophobic amino acids on the protein surface resulting in lower solubility. Removal of the USP45 secretion peptide allowed a soluble and functional invertase to be expressed intracellularly in L. lactis . Immobilized metal affinity chromatography purification of the cell lysate with nickel-NTA gave a single protein band on SDS-PAGE, while E. coli -expressed invertase consistently co-purified with an additional band. The yields of the purified invertase from E. coli and L. lactis were 14.1 and 6.3 mg/l respectively. Conclusions Invertase can be expressed in L. lactis and purified in a functional form. L. lactis is a suitable host for the production of food-grade invertase for use in the food and biotechnology industries.