Role of NAD binding and catalytic residues in the C‐terminal binding protein corepressor

CtBP corepressor proteins potentiate the activity of many metazoan transcriptional repressors. These proteins are homologous to prokaryotic D‐2‐hydroxyacid dehydrogenases, possessing an NAD/NADH binding fold and conserved active site residues. When expressed in Drosophila, a catalytic site mutant retains biological activity, however, we find that an NAD binding mutant lacks biological activity. The NAD mutant, similar to a dimerization mutant, is expressed at low levels, indicating that binding of NAD/NADH may affect CtBP stability. These data support the idea that the ancestral dehydrogenase activity is not required for CtBP function, and NAD binding may play a regulatory, rather than catalytic, role.