de Las Rivas Blanca, Fox Gavin C, Angulo Iván, Ripoll Martín M, Rodríguez Héctor, Muñoz Rosario, Mancheño José M
Departamento de Microbiología, Instituto de Fermentaciones Industriales, CSIC, Madrid, Spain.
J Mol Biol. 2009 Oct 23;393(2):425-34. doi: 10.1016/j.jmb.2009.08.002. Epub 2009 Aug 8.
Catabolic ornithine transcarbamylase (cOTC; EC 2.1.3.3) catalyzes the formation of ornithine (ORN) and carbamoyl phosphate from citrulline, which constitutes the second step of the degradation of arginine via the arginine deiminase pathway. Here, we report the crystal structure of cOTC from the lactic acid bacteria Lactobacillus hilgardii (Lh-cOTC) refined to 2.1 A resolution. The structure reveals that Lh-cOTC forms a hexameric assembly, which was also confirmed by gel-filtration chromatography and analytical ultracentrifugation. The homohexamer, with 32 point group symmetry, represents a new oligomeric state within the members of the ornithine transcarbamylase family that are typically homotrimeric or homododecameric. The C-terminal end from each subunit constitutes a key structural element for the stabilization of the hexameric assembly in solution. Additionally, the structure reveals, for the first time in the ornithine transcarbamylase family, a metal-binding site located at the 3-fold molecular symmetry axis of each trimer.
分解代谢型鸟氨酸转氨甲酰酶（cOTC；EC 2.1.3.3）催化由瓜氨酸形成鸟氨酸（ORN）和氨甲酰磷酸，这是精氨酸通过精氨酸脱亚氨酶途径降解的第二步。在此，我们报道了来自乳酸杆菌希氏乳杆菌（Lh-cOTC）的cOTC晶体结构，其分辨率提高到了2.1埃。该结构表明Lh-cOTC形成六聚体组装，凝胶过滤色谱法和分析超速离心法也证实了这一点。具有32点群对称性的同型六聚体代表了鸟氨酸转氨甲酰酶家族成员中的一种新的寡聚状态，该家族成员通常为同型三聚体或同型十二聚体。每个亚基的C末端是溶液中六聚体组装稳定的关键结构元件。此外，该结构首次在鸟氨酸转氨甲酰酶家族中揭示了一个位于每个三聚体3倍分子对称轴上的金属结合位点。
