InterPro domain: IPR038110

Threonine deaminase (threonine dehydratase, TD) is the first enzyme on the pathway for the biosynthesis of isoleucine. TD is organized into two domains. The larger N-terminal domain is considered the catalytic domain as it contains the essential pyridoxal phosphate cofactor. The C-terminal regulatory domain folds as an eight-stranded antiparallel sheet. The holoenzyme is a homotetramer in which the intersubunit contacts lie between pairs of C-terminal regulatory domains and pairs of N-terminal domains [ 1 ].

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) [ 2 ]. 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. There is a close structural and functional relationship between the regulatory domain of TD and the ACT domain [ 3 ].

1. Structure and control of pyridoxal phosphate dependent allosteric threonine deaminase. Structure 6, 465-75
2. Gleaning non-trivial structural, functional and evolutionary information about proteins by iterative database searches. J. Mol. Biol. 287, 1023-40
3. The ACT domain family. Curr. Opin. Struct. Biol. 11, 694-700