Hoffman and co-workers generated a structure model of EnSynA1, which activates D-αhydroxyisovaleric acid in enniatin biosynthesis, and biochemical characterization of several mutants revealed the importance of key residues. These broadly confirmed the structural findings described above, with G680 (EnSyn numbering) being required for substrate access at the entrance of the binding cavity much like A223 in engineered TycA, and S773 and G767 (EnSyn numbering) providing critical hydrogen bonds through their backbone carbonyl atoms like L313 in native TycA .