A protein comprising a moiety of 100-160 amino acid residues having at least 70% identity with the N-terminal (NT) fragment of a spider silk protein, wherein the amino acid residue corresponding to position 40 in NT is selected from the group consisting of Lys, Arg and His; and wherein the amino acid residue corresponding to position 65 in NT is selected from the group consisting of Asp and Glu, is useful as a moiety in a fusion protein for enhancing the solubility of another moiety in the fusion protein, which is a desired protein or polypeptide.