期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2012
卷号：109
期号：30
页码：11999-12004
DOI：10.1073/pnas.1209406109
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The heterohexameric minichromosome maintenance (MCM2-7) complex is an ATPase that serves as the central replicative helicase in eukaryotes. During initiation, the ring-shaped MCM2-7 particle is thought to open to facilitate loading onto DNA. The conformational state accessed during ring opening, the interplay between ATP binding and MCM2-7 architecture, and the use of these events in the regulation of DNA unwinding are poorly understood. To address these issues in isolation from the regulatory complexity of existing eukaryotic model systems, we investigated the structure/function relationships of a naturally minimized MCM2-7 complex from the microsporidian parasite Encephalitozoon cuniculi. Electron microscopy and small-angle X-ray scattering studies show that, in the absence of ATP, MCM2-7 spontaneously adopts a left-handed, open-ring structure. Nucleotide binding does not promote ring closure but does cause the particle to constrict in a two-step process that correlates with the filling of high- and low-affinity ATPase sites. Our findings support the idea that an open ring forms the default conformational state of the isolated MCM2-7 complex, and they provide a structural framework for understanding the multiphasic ATPase kinetics observed in different MCM2-7 systems.
