Ketol-acid reductoisomerase, N-terminal (IPR013116)

Short name: KARI_N

Overlapping homologous superfamilies

Domain relationships



Ketol-acid reductoisomerase (KARI; (EC:, also known as acetohydroxy acid isomeroreductase (AHIR or AHAIR), catalyzes the conversion of acetohydroxy acids into dihydroxy valerates in the second step of the biosynthetic pathway for the essential branched-chain amino acids valine, leucine, and isoleucine. KARI catalyzes an unusual two-step reaction consisting of an alkyl migration in which the substrate, either 2-acetolactate (AL) or 2-aceto-2-hydroxybutarate (AHB), is converted to 3-hydoxy-3-methyl-2- oxobutyrate or 3-hydoxy-3-methyl-2-pentatonate, followed by a NADPH-dependent reduction to give 2,3-dihydroxy-3-isovalerate or 2,3-dihydroxy-3- methylvalerate respectively [PMID: 9218783, PMID: 11352718, PMID: 12691757, PMID: 16322583, PMID: 25849365, PMID: 26644020].

KARI is present only in bacteria, fungi, and plants, but not in animals. KARIs are divided into two classes on the basis of sequence length and oligomerization state. Class I KARIs are ~340 amino acid residues in length and include all fungal KARIs, whereas class II KARIs are ~490 residues long and include all plant KARIs. Bacterial KARIs can be either class I or class II. KARIs are composed of two types of domains, an N-terminal Rossmann fold domain and one or two C-terminal knotted domains. Two intertwinned knotted domains are required for function, and in the short-chain or class I KARIs, each polypeptide chain has one knotted domain. As a result, dimerization of two monomers forms two complete KARI active sites. In the long-chain or class II KARIs, a duplication of the knotted domain has occurred and, as a result, the protein does not require dimerization to complete its active site [PMID: 9218783, PMID: 11352718, PMID: 12691757, PMID: 16322583, PMID: 25849365, PMID: 26644020].

The alpha/beta KARI N-terminal Rossmann fold domain consists of a nine-stranded mixed beta-sheet with flanking alpha-helices on both sides of the beta-sheet.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles