结构效应的结果绑定到T的天冬氨酸carbamoyltransferase:晶体结构的unligated和ATP, CTP-complexed酶2.6 a分辨率。
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史蒂文斯RC, Gouaux我,以至于WN
结构效应的结果绑定到T的天冬氨酸carbamoyltransferase:晶体结构的unligated和ATP, CTP-complexed酶2.6 a分辨率。
生物化学。1990年8月21日,29 (33):7691 - 701。
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2271528 (在PubMed]
- 文摘
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大肠杆菌天冬氨酸盐的晶体结构carbamoyltransferase口感与腺苷三磷酸(ATP)已经解决分子置换和精制的晶体剩余0.17 2.6 a分辨率使用计算机程序X-PLOR。这种晶体形式的单胞尺寸a = b = 122.2 a和c = 143.3 P321和空间群。虽然c-axis单胞尺寸大约是1比相应的维度CTP-ligated P321晶体形式(c = 142.2), ATP-ligated酶采用一个喜欢四级结构。的基本一半ATP与残留Glu10, Ile12,和Lys60而核糖Asp19和Lys60附近;三磷酸实体必然Lys94,尽管His20和Arg96附近。我们观察到一个更高的入住率的ATP R1监管链的别构部位相比的入住率R6别构部位。这些结晶学独立网站相关的分子2倍轴。有其他违反noncrystallographic对称中所观察到的类似的精制CTP-ligated天冬氨酸carbamoyltransferase结构。这些侵权行为的分子对称性可能是晶体中分子间相互作用的结果。确保与ATP-ligated结构最有意义的比较,我们提炼之前报道CTP-bound和unligated结构使用X-PLOR晶体残差在0.17和0.18之间。 These X-PLOR refined structures are not significantly different from the initial structures that had been crystallographically refined by a restrained least-squares method. After making all possible comparisons between the CTP- and ATP-ligated and the unligated T-state structures, we find that the most significant differences are located at the allosteric sites and in small changes in the quaternary structures. At the allosteric site, the binding of CTP and ATP successively enlarges the nucleotide binding cavity, particularly in the vicinity of the base. The changes in the quaternary structure can be characterized by an increase in the separation of the catalytic trimers by approximately 0.5 A as ATP binds to the unligated T structure. On the basis of these structural studies, we discuss the relationships between the conformational differences in the allosteric site and the small changes in the quaternary structure within the T form to the possible mechanisms for CTP inhibition and ATP activation.