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Crystal structure of human T-protein of glycine cleavage system at 2.0 A resolution and its implication for understanding non-ketotic hyperglycinemia.
Okamura-Ikeda, Kazuko; Hosaka, Harumi; Yoshimura, Masato; Yamashita, Eiki; Toma, Sachiko; Nakagawa, Atsushi; Fujiwara, Kazuko; Motokawa, Yutaro; Taniguchi, Hisaaki.
Afiliação
  • Okamura-Ikeda K; Institute for Enzyme Research, The University of Tokushima, Tokushima 770-8503, Japan. ikeda@ier.tokushima-u.ac.jp
J Mol Biol ; 351(5): 1146-59, 2005 Sep 02.
Article em En | MEDLINE | ID: mdl-16051266
ABSTRACT
T-protein, a component of the glycine cleavage system, catalyzes the formation of ammonia and 5,10-methylenetetrahydrofolate from the aminomethyl moiety of glycine attached to the lipoate cofactor of H-protein. Several mutations in the human T-protein gene cause non-ketotic hyperglycinemia. To gain insights into the effect of disease-causing mutations and the catalytic mechanism at the molecular level, crystal structures of human T-protein in free form and that bound to 5-methyltetrahydrofolate (5-CH3-H4folate) have been determined at 2.0 A and 2.6 A resolution, respectively. The overall structure consists of three domains arranged in a cloverleaf-like structure with the central cavity, where 5-CH3-H4folate is bound in a kinked shape with the pteridine group deeply buried into the hydrophobic pocket and the glutamyl group pointed to the C-terminal side surface. Most of the disease-related residues cluster around the cavity, forming extensive hydrogen bonding networks. These hydrogen bonding networks are employed in holding not only the folate-binding space but also the positions and the orientations of alpha-helix G and the following loop in the middle region, which seems to play a pivotal role in the T-protein catalysis. Structural and mutational analyses demonstrated that Arg292 interacts through water molecules with the folate polyglutamate tail, and that the invariant Asp101, located close to the N10 group of 5-CH3-H4folate, might play a key role in the initiation of the catalysis by increasing the nucleophilic character of the N10 atom of the folate substrate for the nucleophilic attack on the aminomethyl lipoate intermediate. A clever mechanism of recruiting the aminomethyl lipoate arm to the reaction site seems to function as a way of avoiding the release of toxic formaldehyde.
Assuntos
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Bases de dados: MEDLINE Assunto principal: Cristalografia por Raios X / Hidroximetil e Formil Transferases / Hiperglicinemia não Cetótica / Glicina Limite: Animals / Humans Idioma: En Revista: J Mol Biol Ano de publicação: 2005 Tipo de documento: Article País de afiliação: Japão
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Bases de dados: MEDLINE Assunto principal: Cristalografia por Raios X / Hidroximetil e Formil Transferases / Hiperglicinemia não Cetótica / Glicina Limite: Animals / Humans Idioma: En Revista: J Mol Biol Ano de publicação: 2005 Tipo de documento: Article País de afiliação: Japão