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Publication Abstract from PubMed

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 protein-bound 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.

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.,Okamura-Ikeda K, Hosaka H, Maita N, Fujiwara K, Yoshizawa AC, Nakagawa A, Taniguchi H J Biol Chem. 2010 Jun 11;285(24):18684-92. Epub 2010 Apr 6. PMID:20375021^[1]

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