Patent ID: 8603781

Claim:
A method for reducing the incorporation of norleucine into a heterologous protein expressed by a microorganism comprising: modifying a microorganism to co-express a heterologous protein and a non-standard amino acid degrading protein, wherein the expression of the non-standard amino acid degrading protein is increased relative to its expression in the microorganism before said modifying step; and wherein the non-standard amino acid degrading protein comprises: (1) a wild-type Escherichia coli glutamate dehydrogenase, or (2) a variant Escherichia coli glutamate dehydrogenase having an amino acid sequence such that there is a leucine at the amino acid position that corresponds to amino acid position 92 of said wild-type glutamate dehydrogenase, wherein the amino acid at position 92 of said wild-type glutamate dehydrogenase is a lysine, the remainder of the amino acid sequence of the variant consisting essentially of the amino acid sequence of wild type Escherichia coli glutamate dehydroqenase; the method being characterized in that norleucine incorporation into the heterologous protein is reduced when the microorganism is grown in a minimal culture medium which has not been supplemented with methionine.