InterPro domain: IPR002912

The ACT domain is found in a variety of contexts and is proposed to be a conserved regulatory binding fold. ACT domains are linked to a wide range of metabolic enzymes that are regulated by amino acid concentration. The archetypical ACT domain is the C-terminal regulatory domain of 3-phosphoglycerate dehydrogenase (3PGDH), which folds with a ferredoxin-like topology. A pair of ACT domains form an eight-stranded antiparallel sheet with two molecules of allosteric inhibitor serine bound in the interface. Biochemical exploration of a few other proteins containing ACT domains supports the suggestions that these domains contain the archetypical ACT structure [ 1 ].

Most of the proteins in which it is found are involved in amino acid and purine metabolism:

• aspartokinases
• chorismate mutases
• prephenate dehydrogenases (TyrA)
• prephenate dehydratases
• homoserine dehydrogenases
• malate dehydrogenases
• phosphoglycerate dehydrogenases
• phenylalanine and tryptophan-4-monooxygenases
• phosphoribosylformylglycinamidine synthase (PurQ)
• uridylyl transferase and removing enzyme (GlnD)
• GTP pyrophosphokinase/phosphohydrolase (SpoT/RelA)
• tyrosine and phenol metabolism operon regulators (TyrR)
• several uncharacterised proteins from archaea, bacteria and plants that contain from one to four copies of this domain [ 2 ].

1. The ACT domain family. Curr. Opin. Struct. Biol. 11, 694-700
2. Molecular characterization of a novel gene family encoding ACT domain repeat proteins in Arabidopsis. Plant Physiol. 130, 1797-806