A soluble fusion protein is disclosed. The soluble fusion protein comprises at least one soluble polypeptide and a heterologous polypeptide being fused thereto, the heterologous polypeptide being normally insoluble and/or suboptimally expressed when expressed in a cell, wherein the at least one soluble polypeptide has an amino acid sequence at least 65 percent similar to SEQ ID NO: 1 and/or 2, as determined using the Standard protein-protein BLAST [blastp] software of the NCBI.