Signal peptides from filamentous fungi efficiently mediate the secretion of recombinant proteins in Kluyveromyces lactis

• Nine filamentous fungal signal peptides are evaluated for enhanced secretory protein production in Kluyveromyces lactis.
• Efficiency of secretion signal in K. lactis is proven by EGFP expression.
• β glucosidase, glucoamylase and oryzin signal peptide is highly effective in secretion of recombinant protein in K. lactis.
• Secretion of EGFP by fungal signal peptides is improved by codon optimization and Kex2 site addition.

Kluyveromyces lactis is an established host for the secretory production of heterologous proteins. The secretion of enhanced green fluorescent protein (EGFP) in K. lactis mediated by nine secretion signals originating from different filamentous fungi – Aspergillus niger, Aspergillus nidulans, Aspergillus terreus, Aspergillus awamori and Trichoderma reesei were investigated. EGFP was fused to the carboxyl terminus of signals and was expressed under the control of the lac4 promoter. In all the cases, EGFP was secreted into the extracellular fluid. SDS-polyacrylamide gel electrophoresis, western blot analysis of the culture supernatant, and fluorescence measurements confirmed the efficient secretion of EGFP mediated by the novel secretion sequences. In addition, we confirmed that codon optimization and addition of kex2 protease cleavage site in filamentous fungal signal peptide elevated the expression level of recombinant proteins. Efficiency of fungal signal peptide in secretion of other heterologous proteins was demonstrated through secretion of recombinant human interferon β.