Requirement of the N-terminus for dimer formation of phenylalanine-sensitive 3-deoxy-D-arabino-heptulosonate synthase AroG of Escherichia coli

The first regulatory step in the synthesis of aromatic amino acids is catalyzed by 3-deoXy-D-arabinoheptulosonate 7-phosphate synthase (DAHPS). In Escherichia coli, the allosteric DAHPS exists as three isozymes, AroG, AroF and AroH, each independently feedback-inhibited by corresponding end product amino acids, phenylalanine, tyrosine and typtophan. Structural biological evidences have suggested that the N-terminus of AroG is involved in the formation of a putative inhibitor-binding site and feedback inhibition signal transmission. Our previous work showed that a single amino acid residue replacement Ile10Ala or deletion of 15 N-terminal amino acids could lead to a dramatic loss of AroG enzymatic activity (HU et aL 2003). Here we demonstrate that the deletion of N-terminus prevents the enzyme from forming a dimeric structure, indicating that the N-terminus of AroG plays a critical role in the formation of the essential tight dimeric structure.