Functions in the biosynthesis of branched-chain amino acids. Catalyzes the dehydration of (2R,3R)-2,3-dihydroxy-3-methylpentanoate (2,3-dihydroxy-3-methylvalerate) into 2-oxo-3-methylpentanoate (2-oxo-3-methylvalerate) and of (2R)-2,3-dihydroxy-3-methylbutanoate (2,3-dihydroxyisovalerate) into 2-oxo-3-methylbutanoate (2-oxoisovalerate), the penultimate precursor to L-isoleucine and L-valine, respectively. (2R)-2,3-dihydroxy-3-methylbutanoate = 3-methyl-2-oxobutanoate + H2O (2R,3R)-2,3-dihydroxy-3-methylpentanoate = (S)-3-methyl-2-oxopentanoate + H2O Binds 1 [2Fe-2S] cluster per subunit. This cluster acts as a Lewis acid cofactor. Amino-acid biosynthesis; L-isoleucine biosynthesis; L-isoleucine from 2-oxobutanoate: step 3/4. Amino-acid biosynthesis; L-valine biosynthesis; L-valine from pyruvate: step 3/4. Homodimer. Positively regulated by the IlvR protein. Belongs to the IlvD/Edd family.