InterPro domain: IPR011827

This entry is most closely related to the 3-isopropylmalate dehydratase IPR004431 . It includes methanogen homoaconitase small subunit HacB from Methanocaldococcus jannaschii [ 1 , 2 ], 3-isopropylmalate dehydratase small subunit LeuD from Salmonella typhimurium [ 3 ], 2,3-dimethylmalate dehydratase small subunit DmdB from Eubacterium barkeri [ 4 ] and AM-toxin AMT8, an aconitase, from Alternaria alternata [ 5 ].

The structure of the Pyrococcus horikoshii small subunit ( O59393 ) has recently been determined [ 6 ]. As expected the structure of this polypeptide is similar to that of aconitase domain 4, though one alpha helix is replaced by a short loop with relatively high temperature factor values. This loop region is thought to be important for substrate recognition. Unlike other aconitase family proteins, this subunit formed a tetramer through disulphide linkages, though it is not expected to interfere with its interaction with the large subunit. These disulphide linkages would be expected to confer thermostability on the enzyme, reflecting the thermophilic lifestyle of the organism.

1. Methanogen homoaconitase catalyzes both hydrolyase reactions in coenzyme B biosynthesis. J. Biol. Chem. 283, 28888-96
2. Substrate specificity determinants of the methanogen homoaconitase enzyme: structure and function of the small subunit. Biochemistry 49, 2687-96
3. Characterization of the 3' end of the leucine operon of Salmonella typhimurium. Mol. Gen. Genet. 199, 486-94
4. Nicotinic acid metabolism. Dimethylmaleate hydratase. Hoppe-Seyler's Z. Physiol. Chem. 365, 847-57
5. Cloning and characterization of a cyclic peptide synthetase gene from Alternaria alternata apple pathotype whose product is involved in AM-toxin synthesis and pathogenicity. Mol. Plant Microbe Interact. 13, 742-53
6. Crystal structure of the Pyrococcus horikoshii isopropylmalate isomerase small subunit provides insight into the dual substrate specificity of the enzyme. J. Mol. Biol. 344, 325-33