The present invention relates to polypeptides comprising hemolysin A (HlyA) fragments and/or variants and a peptide or polypeptide of interest in form of a fusion protein that exhibits improved expression and secretion as well as increased solubility and stability and improved renaturation efficiency. Also encompassed are nucleic acids encoding these polypeptides, host cells that comprise said nucleic acids, and methods and uses for protein expression using said nucleic acids, host cells and polypeptides.