The present invention concerns a protein mixture comprising at least a first fusion protein comprising a protein or protein fragment, and an interaction domain and a protein translocation sequence, which effects that the fusion protein upon expression in a bacterium is translocated through the cytoplasmic membrane in an essentially unfolded state and at least a second fusion protein comprising a protein or protein fragment, and an interaction domain and a protein translocation sequence which effects that the fusion protein is translocated through the cytoplasmic membrane upon expression in a bacterium in an essentially folded state, wherein the interaction domain of the first protein can bind to those of the second protein.
