Rational Engineering of Homoserine O-Succinyltransferase from Escherichia coli for Reduced Feedback Inhibition by Methionine.

Methionine is an essential amino acid in all living organisms and has been used in various industrial applications such as food and feed additives. However, inhibition of enzymes involved in methionine biosynthesis is considered to be a crucial bottleneck for an efficient bio-based methionine production process. Homoserine O-succinyltransferase from Escherichia coli ( Ec HST) has been reported to be feedback inhibited by the final product methionine. To understand the regulation mechanism of the enzyme and generate a feedback-resistant mutant, we determined the crystal structure of Ec HST and elucidated the binding site of homoserine and succinyl-CoA. The enzyme kinetic experiments of Ec HST revealed that the enzyme is noncompetitively inhibited by methionine with a K i value of 2.44 mM, and we also identified a putative inhibitor binding site located in the vicinity of the substrate binding site. We then generated the Ec HST T242A variant with reduced feedback inhibition with a K i value of 17.40 mM.