A method of producing a desired non-spidroin protein or polypeptide is comprising the steps of expressing in a suitable host a fusion protein, obtaining a mixture containing the fusion protein, and optionally isolating the fusion protein. The fusion protein is comprising at least one solubility-enhancing moiety which is derived from the N-terminal (NT) fragment of a spider silk protein. It is further comprising at least one moiety which is a desired non-spidroin protein or polypeptide. Each solubility-enhancing moiety is linked directly or indirectly to the desired protein or polypeptide moiety.