The present invention relates to genetically modified host cells, in particular yeast cells, comprising at least one isolated polynucleotide encoding a Killer Expression protease (Kex2p) or a fragment and/or variant thereof which has at least one Kex2p functional activity and at least one isolated polynucleotide encoding a Protein Disulfide- Isomerase (Pdil) or a fragment and/or variant thereof which has at least one Pdi functional activity. Also provided herein are genetically modified host cells comprising at least one isolated polynucleotide encoding a Killer Expression protease (Kex2p) or a fragment and/or variant thereof which has at least one Kex2p functional activity, at least one isolated polynucleotide encoding a Protein Disulfide -Isomerase (Pdil) or a fragment and/or variant thereof which has at least one Pdil functional activity and at least one isolated polynucleotide encoding a Endoplasmic Reticulum Oxidoreductin (Erol) or a fragment and/or variant thereof which has at least one Erol functional activity.
