Crystallographic study of steps along the reaction pathway of D-amino acid aminotransferase.Peisach, D., Chipman, D.M., Van Ophem, P.W., Manning, J.M., Ringe, D.
(1998) Biochemistry 37: 4958-4967
- PubMed: 9538014
- DOI: https://doi.org/10.1021/bi972884d
- Primary Citation of Related Structures:
- PubMed Abstract:
The three-dimensional structures of two forms of the D-amino acid aminotransferase (D-aAT) from Bacillus sp. YM-1 have been determined crystallographically: the pyridoxal phosphate (PLP) form and a complex with the reduced analogue of the external aldimine, N-(5'-phosphopyridoxyl)-d-alanine (PPDA). Together with the previously reported pyridoxamine phosphate form of the enzyme [Sugio et al. (1995) Biochemistry 34, 9661], these structures allow us to describe the pathway of the enzymatic reaction in structural terms. A major determinant of the enzyme's stereospecificity for D-amino acids is a group of three residues (Tyr30, Arg98, and His100, with the latter two contributed by the neighboring subunit) forming four hydrogen bonds to the substrate alpha-carboxyl group. The replacement by hydrophobic groups of the homologous residues of the branched chain L-amino acid aminotransferase (which has a similar fold) could explain its opposite stereospecificity. As in L-aspartate aminotransferase (L-AspAT), the cofactor in D-aAT tilts (around its phosphate group and N1 as pivots) away from the catalytic lysine 145 and the protein face in the course of the reaction. Unlike L-AspAT, D-aAT shows no other significant conformational changes during the reaction.
Program in Bioorganic Chemistry, Brandeis University, 415 South Street, Waltham, Massachusetts 02254-9110, USA.