4ysn

Publication Abstract from PubMed

Crystal structures of Lactobacillus buchneri isoleucine 2-epimerase, a novel branched-chain amino-acid racemase, were determined for the enzyme in the apo form, in complex with pyridoxal 5'-phosphate (PLP), in complex with N-(5'-phosphopyridoxyl)-L-isoleucine (PLP-L-Ile) and in complex with N-(5'-phosphopyridoxyl)-D-allo-isoleucine (PLP-D-allo-Ile) at resolutions of 2.77, 1.94, 2.65 and 2.12 A, respectively. The enzyme assembled as a tetramer, with each subunit being composed of N-terminal, C-terminal and large PLP-binding domains. The active-site cavity in the apo structure was much more solvent-accessible than that in the PLP-bound structure. This indicates that a marked structural change occurs around the active site upon binding of PLP that provides a solvent-inaccessible environment for the enzymatic reaction. The main-chain coordinates of the L. buchneri isoleucine 2-epimerase monomer showed a notable similarity to those of alpha-amino--caprolactam racemase from Achromobactor obae and gamma-aminobutyrate aminotransferase from Escherichia coli. However, the amino-acid residues involved in substrate binding in those two enzymes are only partially conserved in L. buchneri isoleucine 2-epimerase, which may account for the differences in substrate recognition by the three enzymes. The structures bound with reaction-intermediate analogues (PLP-L-Ile and PLP-D-allo-Ile) and site-directed mutagenesis suggest that L-isoleucine epimerization proceeds through abstraction of the alpha-hydrogen of the substrate by Lys280, while Asp222 serves as the catalytic residue adding an alpha-hydrogen to the quinonoid intermediate to form D-allo-isoleucine.

Crystal structure of the novel amino-acid racemase isoleucine 2-epimerase from Lactobacillus buchneri.,Hayashi J, Mutaguchi Y, Minemura Y, Nakagawa N, Yoneda K, Ohmori T, Ohshima T, Sakuraba H Acta Crystallogr D Struct Biol. 2017 May 1;73(Pt 5):428-437. doi:, 10.1107/S2059798317005332. Epub 2017 Apr 19. PMID:28471367^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.