Search

This research was originally published in Journal of Biological Chemistry. Kazuko Okamura-Ikeda, Harumi Hosaka, Nobuo Maita, Kazuko Fujiwara, Akiyasu C. Yoshizawa, Atsushi Nakagawa and Hisaaki Taniguchi. Crystal structure of aminomethyltransferase in complex with dihydrolipoyl-H-protein of the glycine cleavage system : Implications for recognition of lipoyl protein substrate, disease-related mutations, and reaction mechanism. Journal of Biological Chemistry. 2010; 285, 18684-18692. © the American Society for Biochemistry and Molecular Biology., Aminomethyltransferase, a component of the glycine cleavage system termed T-protein, reversibly catalyzes the degradation of the aminomethyl moiety of glycine attached to the lipoate cofactor of H-protein, resulting in the production of ammonia, 5,10-methylenetetrahydrofolate, and dihydrolipoate- bearing H-protein in the presence of tetrahydrofolate. Several mutations in the human T-protein gene are known to cause nonketotic hyperglycinemia. Here, we report the crystal structure of Escherichia coli T-protein in complex with dihydrolipoate-bearing H-protein and 5-methyltetrahydrofolate, a complex mimicking the ternary complex in the reverse reaction. The structure of the complex shows a highly interacting intermolecular interface limited to a small area and the proteinbound dihydrolipoyllysine arm inserted into the active site cavity of the T-protein. Invariant Arg^292 of the T-protein is essential for complex assembly. The structure also provides novel insights in understanding the disease-causing mutations, in addition to the disease-related impairment in the cofactor-enzyme interactions reported previously. Furthermore, structural and mutational analyses suggest that the reversible transfer of the methylene group between the lipoate and tetrahydrofolate should proceed through the electron relay-assisted iminium intermediate formation.

This research was originally published in Journal of Biological Chemistry. Kazuko Fujiwara, Sachiko Toma, Kazuko Okamura-Ikeda, Yutaro Motokawa, Atsushi Nakagawa and Hisaaki Taniguchi. Crystal structure of lipoate-protein ligase A from Escherichia coli : Determination of the lipoic acid-binding site. Journal of Biological Chemistry. 2005; 280, 33645-33651. © the American Society for Biochemistry and Molecular Biology., Lipoate-protein ligase A (LplA) catalyzes the formation of lipoyl-AMP from lipoate and ATP and then transfers the lipoyl moiety to a specific lysine residue on the acyltransferase subunit of α-ketoacid dehydrogenase complexes and on H-protein of the glycine cleavage system. The lypoyllysine arm plays a pivotal role in the complexes by shuttling the reaction intermediate and reducing equivalents between the active sites of the components of the complexes. We have determined the X-ray crystal structures of Escherichia coli LplA alone and in a complex with lipoic acid at 2.4 and 2.9 Å resolution, respectively. The structure of LplA consists of a large N-terminal domain and a small C-terminal domain. The structure identifies the substrate binding pocket at the interface between the two domains. Lipoic acid is bound in a hydrophobic cavity in the N-terminal domain through hydrophobic interactions and a weak hydrogen bond between carboxyl group of lipoic acid and the Ser-72 or Arg-140 residue of LplA. No large conformational change was observed in the main chain structure upon the binding of lipoic acid.

This research was originally published in Journal of Biological Chemistry. Kazuko Fujiwara, Nobuo Maita, Harumi Hosaka, Kazuko Okamura-Ikeda, Atsushi Nakagawa Hisaaki Taniguchi. Global conformational change associated with the two-step reaction catalyzed by Escherichia coli lipoate-protein ligase A. Journal of Biological Chemistry. 2010; 285, 9971-9980. © the American Society for Biochemistry and Molecular Biology., Lipoate-protein ligase A (LplA) catalyzes the attachment of lipoic acid to lipoate-dependent enzymes by a two-step reaction: first the lipoate adenylation reaction and, second, the lipoate transfer reaction. We previously determined the crystal structure of Escherichia coli LplA in its unliganded form and a binary complex with lipoic acid (Fujiwara, K., Toma, S., Okamura- Ikeda, K., Motokawa, Y., Nakagawa, A., and Taniguchi, H. (2005) J Biol. Chem. 280, 33645–33651). Here, we report two new LplA structures, LplAlipoyl-5-AMP and LplAoctyl-5-AMPapoHprotein complexes, which represent the post-lipoate adenylation intermediate state and the pre-lipoate transfer intermediate state, respectively. These structures demonstrate three large scale conformational changes upon completion of the lipoate adenylation reaction: movements of the adenylate-binding and lipoate-binding loops to maintain the lipoyl-5-AMP reaction intermediate and rotation of the C-terminal domain by about 180°. These changes are prerequisites for LplA to accommodate apoprotein for the second reaction. The Lys133 residue plays essential roles in both lipoate adenylation and lipoate transfer reactions. Based on structural and kinetic data, we propose a reaction mechanism driven by conformational changes.