3-Hydroxyisobutyrate is a central metabolite in the valine catabolic pathway, and is reversibly oxidised to methylmalonate semi-aldehyde by a specific dehydrogenase belonging to the 3-hydroxyacid dehydrogenase family. The reaction is NADP-dependent and this region of the enzyme binds NAD. The NAD-binding domain of 6-phosphogluconate dehydrogenase adopts an alpha helical structure [1].

1: Crystal structure of novel NADP-dependent 3-hydroxyisobutyrate dehydrogenase from Thermus thermophilus HB8. Lokanath NK, Ohshima N, Takio K, Shiromizu I, Kuroishi C, Okazaki N, Kuramitsu S, Yokoyama S, Miyano M, Kunishima N; J Mol Biol. 2005;352:905-917. PMID:16126223