T-State Active Site of Aspartate Transcarbamylase: Crystal Structure of the Carbamyl Phosphate and L-Alanosine Ligated Enzyme

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• 作者：Jingwei Huang and William N. Lipscomb
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：January 17, 2006
• 年：2006
• 卷：45
• 期：2
• 页码：346 - 352
• 全文大小：242K
• 年卷期：v.45,no.2(January 17, 2006)
• ISSN：1520-4995

文摘

An X-ray diffraction study to 2.0 Å resolution shows that this enzyme, ATCase, is in theT-state (the c₃ to c₃ distance is 45.2 Å) when ATCase is bound to carbamyl phosphate (CP) and toL-alanosine (an analogue of aspartate). This result strongly supports the kinetic results that alanosine didnot inhibit the carbamylation of aspartate in the normal reaction of native ATCase plus CP and aspartate[Baillon, J., Tauc, P., and Hervé, G. (1985) Biochemistry 24, 7182-7187]. The structure further revealsthat the phosphate of CP is 4 Å away from its known position in the R-state and is in the T-state positionof P_i in a recent study of ATCase complexed with products, phosphate (P_i) and N-carbamyl-L-aspartate[Huang, J., and Lipscomb, W. N. (2004) Biochemistry 43, 6422-6426]. Moreover, the alanosine positionin this T-state is somewhat displaced from that expected for its analogue, aspartate, from the R-stateposition. The relations of these structural aspects to the kinetics are presented.