Breyer W A, Matthews B W
Institute of Molecular Biology, Howard Hughes Medical Institute, 1229 University of Oregon, Eugene, Oregon 97403-1229, USA.
Nat Struct Biol. 2000 Dec;7(12):1125-8. doi: 10.1038/81978.
Exonuclease I (ExoI) from Escherichia coli is a monomeric enzyme that processively degrades single stranded DNA in the 3' to 5' direction and has been implicated in DNA recombination and repair. Determination of the structure of ExoI to 2.4 A resolution using X-ray crystallography verifies the expected correspondence between a region of ExoI and the exonuclease (or proofreading) domains of the DNA polymerases. The overall fold of ExoI also includes two other regions, one of which extends the exonuclease domain and another that can be described as an elaborated SH3 domain. These three regions combine to form a molecule that is shaped like the letter C, although it also contains a segment that effectively converts the C into an O-like shape. The structure of ExoI thus provides additional support for the idea that DNA metabolizing enzymes achieve processivity by completely enclosing the DNA.
来自大肠杆菌的核酸外切酶I（ExoI）是一种单体酶，它能沿3'到5'方向持续降解单链DNA，并参与DNA重组和修复。利用X射线晶体学将ExoI的结构解析到2.4埃的分辨率，证实了ExoI的一个区域与DNA聚合酶的核酸外切酶（或校对）结构域之间预期的对应关系。ExoI的整体折叠还包括另外两个区域，其中一个区域延伸了核酸外切酶结构域，另一个区域可描述为一个精细的SH3结构域。这三个区域结合形成一个形状像字母C的分子，不过它还包含一个能有效将C形转变为类似O形的片段。因此，ExoI的结构为DNA代谢酶通过完全包裹DNA来实现持续合成的观点提供了额外支持。
