Structure of the imine reductase from Ajellomyces dermatitidis in three crystal forms.

The NADPH-dependent imine reductase from Ajellomyces dermatitidis (AdRedAm) catalyzes the reductive amination of certain ketones with amine donors supplied in an equimolar ratio. The structure of AdRedAm has been determined in three forms. The first form, which belongs to space group P3₁21 and was refined to 2.01 Å resolution, features two molecules (one dimer) in the asymmetric unit in complex with the redox-inactive cofactor NADPH₄. The second form, which belongs to space group C2₁ and was refined to 1.73 Å resolution, has nine molecules (four and a half dimers) in the asymmetric unit, each complexed with NADP⁺. The third form, which belongs to space group P3₁21 and was refined to 1.52 Å resolution, has one molecule (one half-dimer) in the asymmetric unit. This structure was again complexed with NADP⁺ and also with the substrate 2,2-difluoroacetophenone. The different data sets permit the analysis of AdRedAm in different conformational states and also reveal the molecular basis of stereoselectivity in the transformation of fluorinated acetophenone substrates by the enzyme.