CRYSTAL AND MOLECULAR-STRUCTURES OF NATIVE AND CTP-LIGANDED ASPARTATE CARBAMOYLTRANSFERASE FROM ESCHERICHIA-COLI
CRYSTAL AND MOLECULAR-STRUCTURES OF NATIVE AND CTP-LIGANDED ASPARTATE CARBAMOYLTRANSFERASE FROM ESCHERICHIA-COLI
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DOI：
10.1016/0022-2836(82)90175-9
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发表时间：
1982-01-01
影响因子：
5.6
通讯作者：
LIPSCOMB, WN
中科院分区：
文献类型：
--
作者：
HONZATKO, RB;CRAWFORD, JL;LIPSCOMB, WN
本文用原子模型描述了两种天冬氨酸氨甲酰转移酶晶体的电子密度。大肠杆菌的感染。未配体形式（R32晶体对称性）和CTP-配体形式（P3211晶体对称性）在3.0埃的分辨率下独立精制。和2.8.分别地，每一个晶体学R因子为27%。分子模型包括基于化学序列信息的天冬氨酸氨甲酰基转移酶分子的至少95%的理论原子数。提供了2种结构的细化过程的细节，并评价了分子模型的准确性。在大多数情况下，未配体化的酶和CTP配体化的形式的调节和催化链具有相似的构象。CTP和天然形式存在较大的构象差异，特别是在CTP与调节链结合的区域。一段10个氨基酸残基，其中包括Lys 83和Lys 84的催化链，是无序的CTP配体的形式，与天然结构，其中相同的残基已经细化到密度。天冬氨酸氨甲酰转移酶的每个催化单体与3个催化链和2个调节单体接触。每个调节单体与1条其他调节链和2条催化链相邻。催化三聚体在六聚体中接触;对同向效应和催化作用重要的残基（Tyr 165和Tyr 232）是界面的组成部分。一个彻底的调查界面区域和整个分子的侧链之间的极性相互作用进行编目。并对酶的化学修饰和突变进行了讨论。特别强调的是Cys 47、Tyr 165和Tyr 232、Lys 83、Lys 84、Trp 209和Trp 279以及Gly 128，这些残基对天冬氨酸氨甲酰转移酶的催化或调节功能具有重要性。活性位点残基的空间排列证明了催化亚基内2个单体之间共享的催化口袋。
Atomic models representing the electron density of 2 crystalline forms of aspartate carbamoyltransferase from E. coli are reported. The unliganded form (R32 crystal symmetry) and the CTP-liganded from (P3211 crystal symmetry) were refined independently at resolution of 3.0 .ANG. and 2.8 .ANG., respectively, each to a crystallographic R-factor of 27%. The molecular models include at least 95% of the theoretical number of atoms for the aspartate carbamoyltransferase molecule based on chemical sequence information. Details of the refinement process for the 2 structures are provided, and the accuracy of the molecular models was evaluated. For the most part, the regulatotry and catalytic chains of the unliganded enzyme and the CTP-liganded form are in similar conformations. Large conformational differences in the CTP and native forms exist, specifically in the region of CTP binding to the regulatory chain. A segment of 10 amino acid residues, which includes Lys83 and Lys84 of the catalytic chain, is disordered in the CTP-liganded form, in contrast to the native structure, where the same residues have refined well into density. Each catalytic monomer of aspartate carbamoyltransferase is in contact with 3 catalytic chains and 2 regulatory monomers. Each regulatory monomer borders in 1 other regulatory chain and 2 catalytic chains. The catalytic trimers are in contact in the hexamer; residues important to homotropic effects and catalysis (Tyr165 and Tyr232) are integral parts of the interface. A thorough survey of interface regions is presented and polar interactions between side-chains throughout the molecule are catalogued. The chemical modifications and mutations of the enzyme were also discussed. Highlighted specifically are Cys47, Tyr165 and Tyr232, Lys83, Lys84, Trp209 and Trp279 and Gly128, residues of demonstrated importance to the catalytic or regulatory function of aspartate carbamoyltransferase. The spatial arrangement of active site residues argues for a catalytic pocket shared between 2 monomers within a catalytic subunit.