In enzymology, a 3-hydroxy-2-methylbutyryl-CoA dehydrogenase (EC 184.108.40.206) is an enzyme that catalyzes the chemical reaction
- (2S,3S)-3-hydroxy-2-methylbutanoyl-CoA + NAD+ 2-methylacetoacetyl-CoA + NADH + H+
Thus, the two substrates of this enzyme are (2S,3S)-3-hydroxy-2-methylbutanoyl-CoA and NAD+, whereas its 3 products are 2-methylacetoacetyl-CoA, NADH, and H+.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is (2S,3S)-3-hydroxy-2-methylbutanoyl-CoA:NAD+ oxidoreductase. Other names in common use include 2-methyl-3-hydroxybutyryl coenzyme A dehydrogenase, 2-methyl-3-hydroxybutyryl coenzyme A dehydrogenase, and 2-methyl-3-hydroxy-butyryl CoA dehydrogenase. This enzyme participates in valine, leucine and isoleucine degradation.
Structural studies 
As of 20 January 2010, 6 structure have been solved for this class of enzymes, with the PDB accession code 1E3S, 1E3W, 1E6W, 1SO8, 1U7T, 2O23.