Streptomyces griseus aminopeptidase: X-ray crystallographic structure at 1.75 angstrom resolution
Streptomyces griseus aminopeptidase: X-ray crystallographic structure at 1.75 angstrom resolution
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DOI：
10.1006/jmbi.1996.0729
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发表时间：
1997-02-07
影响因子：
5.6
通讯作者：
Shoham, G
中科院分区：
文献类型：
--
作者：
Greenblatt, HM;Almog, O;Shoham, G
灰色链霉菌氨肽酶（SGAP）的x射线晶体结构以双锌形式（1.75埃）、以辅酶形式（去锌）（2.1埃）和以汞取代衍生物（2.1埃）的分辨率测定。结构解是通过异常散射（SIRAS）的单次同构替换，然后通过直方图匹配进行密度修正来实现的。这种蛋白质由一个由8条平行和反平行链组成的中央β片组成，两侧被螺旋包围。活性位点位于β -片区两条中间链的羰基端。该链的两个部分无法追踪，分别是与活性位点相邻的Glu196至Arg202，以及以Gly278开头的最后7个c端残基。活性位点包含两个锌阳离子，每个锌阳离子具有相似的配体，彼此之间的距离为3.6埃。一种未知分子似乎与活性部位的锌离子结合在一起，并被模拟为磷酸离子。钙结合位点也被确定，这与钙调节酶的活性并增加其热稳定性的观察结果一致。钙离子调节酶活性的机制尚不清楚，因为钙结合位点的位置与活性位点锌离子相距约25埃。与其他已知的氨肽酶的结构比较表明，SGAP与Aeromonas proteolytica氨肽酶（AAP）最为相似。这两种酶具有相似的拓扑结构，尽管总体序列一致性非常低（24%在对齐区域）。SGAP中两个活性位点锌阳离子的配位与AAP相似。这两种微生物酶与牛晶态亮氨酸氨基肽酶（LAP）在整体结构和两个锌离子的配位上都有所不同。(C) 1997学术出版社有限公司
The X-ray crystal structure of the enzyme Streptomyces griseus aminopeptidase (SGAP) has been determined in its double zinc form to 1.75 Angstrom resolution, in its apo-enzyme form (zinc removed) to 2.1 Angstrom, resolution, and as a mercury replaced derivative to 2.1 Angstrom resolution. The structure solution was achieved by single isomorphous replacement with phasing from anomalous scattering (SIRAS), followed by density modification with histogram matching. The protein consists of a central beta-sheet made up of eight parallel and antiparallel strands, surrounded by helices on either side. The active site is located at the carbonyl ends of two middle strands of the beta-sheet region. Two sections of the chain that could not be traced were Glu196 to Arg202, which borders the active site, and the final seven C-terminal residues starting with Gly278. The active site contains two zinc cations, each with similar ligands, at a distance of 3.6 Angstrom from each other. An unknown molecule appears to be bound to both zinc ions in the active site at partial occupancy and has been modelled as a phosphate ion. A calcium binding site has also been identified, consistent with the observations that calcium modulates the activity of the enzyme, and increases its heat stability. The mechanism by which the calcium cation modulates enzyme activity is not apparent, since the location of the calcium binding site is similar to 25 Angstrom distant from the active site zinc ions. Comparison of the structure of SGAP to other known aminopeptidases shows that the enzyme is most similar to Aeromonas proteolytica aminopeptidase (AAP). Both enzymes share a similar topology, although the overall sequence identity is very low (24% in aligned regions). The coordination of the two active site zinc cations in SGAP resembles that of AAP. These two microbial enzymes differ from bovine lens leucine aminopeptidase (LAP) in both overall structure and in coordination of the two zinc ions. (C) 1997 Academic Press Limited.