Ammon H L, Weber I T, Wlodawer A, Harrison R W, Gilliland G L, Murphy K C, Sjölin L, Roberts J
Department of Chemistry and Biochemistry, University of Maryland, College Park 20742.
J Biol Chem. 1988 Jan 5;263(1):150-6.
The preliminary structure of a glutaminase-asparaginase from Acinetobacter glutaminasificans is reported. The structure was determined at 3.0-A resolution with a combination of phase information from multiple isomorphous replacement at 4-5-A resolution and phase improvement and extension by two density modification techniques. The electron density map was fitted by a polypeptide chain that was initially polyalanine. This was subsequently replaced by a polypeptide with an amino acid sequence in agreement with the sizes and shapes of the side chain electron densities. The crystallographic R factor is 0.300 following restrained least squares refinement with data to 2.9-A resolution. The A. glutaminasificans glutaminase-asparaginase subunit folds into two domains: the aminoterminal domain contains a five-stranded beta sheet surrounded by five alpha helices, while the carboxyl-terminal domain contains three alpha helices and less regular structure. The connectivity is not fully determined at present, due in part to the lack of a complete amino acid sequence. The A. glutaminasificans glutaminase-asparaginase structure has been used successfully to determine the relative orientations of the molecules in crystals of Pseudomonas 7A glutaminase-asparaginase, in crystals of Vibrio succinogenes asparaginase, and in a new crystal form of Escherichia coli asparaginase (space group 1222, one subunit per asymmetric unit).
报道了来自谷氨酰胺酶产生不动杆菌的谷氨酰胺酶 - 天冬酰胺酶的初步结构。该结构在3.0埃分辨率下测定，结合了4 - 5埃分辨率下多同晶置换的相位信息以及通过两种密度修正技术进行的相位改善和扩展。电子密度图由最初为聚丙氨酸的多肽链拟合。随后被一条氨基酸序列与侧链电子密度的大小和形状相符的多肽所取代。在使用2.9埃分辨率数据进行约束最小二乘精修后，晶体学R因子为0.300。谷氨酰胺酶产生不动杆菌的谷氨酰胺酶 - 天冬酰胺酶亚基折叠成两个结构域：氨基末端结构域包含一个由五个α螺旋包围的五链β折叠，而羧基末端结构域包含三个α螺旋和不太规则的结构。目前连接性尚未完全确定，部分原因是缺乏完整的氨基酸序列。谷氨酰胺酶产生不动杆菌的谷氨酰胺酶 - 天冬酰胺酶结构已成功用于确定假单胞菌7A谷氨酰胺酶 - 天冬酰胺酶晶体、琥珀酸弧菌天冬酰胺酶晶体以及大肠杆菌天冬酰胺酶新晶体形式（空间群I222，每个不对称单元一个亚基）中分子的相对取向。
