The ACT domain is a 90 amino acid long domain, which has been named after three of the allosterically regulated enzymes in which it is found: aspartate kinase, chorismate mutase and TyrA (prephenate dehydrogenase) [1]. The ACT domain is found in a variety of contexts and is proposed to be a structurally conserved regulatory domain involved in the binding of small ligands, such as amino acids. 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 uncharacterized proteins from archaea, bacteria and plants that contain from one to four copies of this domain [2].

The ACT domain forms a β-sheet with appressed helices (see <PDB:1PSD>) [1].

Threonine dehydratases (TDs) contain an ACT-like regulatory domain that possesses structural, rather than sequence, homology to the ACT domain [3].

The profile we developed cover the entire ACT and ACT-like domains.