title: Structural determinants of the β-selectivity of a bacterial aminotransferase.
abstract: Chiral β-amino acids occur as constituents of various natural and synthetic compounds with potentially useful bioactivities. The pyridoxal 5'-phosphate (PLP)-dependent S-selective transaminase from Mesorhizobium sp. strain LUK (MesAT) is a fold type I aminotransferase that can be used for the preparation of enantiopure β-Phe and derivatives thereof. Using x-ray crystallography, we solved structures of MesAT in complex with (S)-β-Phe, (R)-3-amino-5-methylhexanoic acid, 2-oxoglutarate, and the inhibitor 2-aminooxyacetic acid, which allowed us to unveil the molecular basis of the amino acid specificity and enantioselectivity of this enzyme. The binding pocket of the side chain of a β-amino acid is located on the 3'-oxygen side of the PLP cofactor. The same binding pocket is utilized by MesAT to bind the α-carboxylate group of an α-amino acid. A β-amino acid thus binds in a reverse orientation in the active site of MesAT compared with an α-amino acid. Such a binding mode has not been reported before for any PLP-dependent aminotransferase and shows that the active site of MesAT has specifically evolved to accommodate both β- and α-amino acids.
authors: Laboratory of Biophysical Chemistry, University of Groningen, 9747 AG Groningen, The Netherlands.
authors: Gjalt G
authors: GG
authors: Wybenga
authors: Ciprian G
authors: CG
authors: Crismaru
authors: Dick B
authors: DB
authors: Janssen
authors: Bauke W
authors: BW
authors: Dijkstra
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry; D007656:Ketoglutaric Acids / Q000737:chemistry; D059128:Mesorhizobium / Q000201:enzymology*; D010649:Phenylalanine / Q000737:chemistry; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity; D000637:Transaminases / Q000737:chemistry* / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D007656:Ketoglutaric Acids; D010649:Phenylalanine; D000637:Transaminases