Crystallographic characterization of the (R)-selective amine transaminase from Aspergillus fumigatus

The importance of amine transaminases for producing optically pure chiral precursors for pharmaceuticals and chemicals has substantially increased in recent years. The X-­ray crystal structure of the (R)-selective amine transaminase from the fungus Aspergillus fumigatus was solved by S-­SAD phasing to 1.84 Å resolution. The refined structure at 1.27 Å resolution provides detailed knowledge about the molecular basis of substrate recognition and conversion to facilitate protein-engineering approaches. The protein forms a homodimer and belongs to fold class IV of the pyridoxal-5'-­phosphate-dependent enzymes. Both subunits contribute residues to form two active sites. The structure of the holoenzyme shows the catalytically important cofactor pyridoxal-5'-phosphate bound as an internal aldimine with the catalytically responsible amino-acid residue Lys179, as well as in its free form. A long N-terminal helix is an important feature for the stability of this fungal (R)-selective amine transaminase, but is missing in branched-chain amino-acid aminotransferases and D-amino-acid aminotransferases.