Disclosed is a mutant FG21 nucleic acid molecule comprising a nucleotide sequence encoding a polypeptide of SEQ ID NO: 4 having a lysine residue at position 36 and at least one amino acid substitution that is: (a) a lysine residue at one or more of positions 72, 77, 126 and 175； (b) a cysteine residue at one or more of positions 37, 38, 46, 91, 69, 77, 79, 87, 91, 112, 113, 120, 121, 125, 126, 175, 170, and 179: (c) an arginine residue at one or more of positions 56, 59, 69, and 122； (d) a glycine residue at position 170； (e) a glycine residue at position 171； and combinations of (a) - (e). Also disclosed is a method for treating metabolic disorders using such nucleic acids. compositions
