Addlagatta Anthony, Gay Leslie, Matthews Brian W
Howard Hughes Medical Institute and Institute of Molecular Biology and Department of Physics, University of Oregon, Eugene, OR 97403-1229.
Proc Natl Acad Sci U S A. 2006 Sep 5;103(36):13339-44. doi: 10.1073/pnas.0606167103. Epub 2006 Aug 28.
Aminopeptidase N from Escherichia coli is a major metalloprotease that participates in the controlled hydrolysis of peptides in the proteolytic pathway. Determination of the 870-aa structure reveals that it has four domains similar to the tricorn-interacting factor F3. The thermolysin-like active site is enclosed within a large cavity with a volume of 2,200 A(3), which is inaccessible to substrates except for a small opening of approximately 8-10 A. The substrate-based inhibitor bestatin binds to the protein with minimal changes, suggesting that this is the active form of the enzyme. The previously described structure of F3 had three distinct conformations that were described as "closed," "intermediate," and "open." The structure of aminopeptidase N from E. coli, however, is substantially more closed than any of these. Taken together, the results suggest that these proteases, which are involved in intracellular peptide degradation, prevent inadvertent hydrolysis of inappropriate substrates by enclosing the active site within a large cavity. There is also some evidence that the open form of the enzyme, which admits substrates, remains inactive until it adopts the closed form.
来自大肠杆菌的氨肽酶N是一种主要的金属蛋白酶，参与蛋白水解途径中肽的可控水解。对其870个氨基酸结构的测定表明，它有四个与三触角相互作用因子F3相似的结构域。类嗜热菌蛋白酶活性位点被封闭在一个体积为2200 ų的大腔内，除了一个约8 - 10 Å的小开口外，底物无法进入该腔。基于底物的抑制剂贝抑素与该蛋白结合时变化极小，这表明这是该酶的活性形式。先前描述的F3结构有三种不同构象，分别被描述为“封闭”“中间”和“开放”。然而，来自大肠杆菌的氨肽酶N的结构比这些构象中的任何一种都要更加封闭。综合来看，结果表明这些参与细胞内肽降解的蛋白酶通过将活性位点封闭在一个大腔内，防止对不合适底物的意外水解。也有一些证据表明，允许底物进入的酶的开放形式在采用封闭形式之前一直无活性。
