Identification of a new molecular mechanism indicates new ways to block the uncontrolled cell division -
In a study published today in Genes & Development Dr. Christian Speck of the replication group from the MRC Clinical Sciences Centre DNA, in collaboration with Brookhaven National Laboratory (BNL), New York, reveals the complex mechanisms involved in enzyme that regulates DNA replication during cell division. By developing a sophisticated system using synthetic, chemical and structural biology approaches, the study reveals how a key enzyme involved in the replication of genetic information through DNA embraces a closed system, which opens at specific positions to a highly regulated replication process. This work improves the current understanding of an essential biological process and suggests a way to stop cell division in diseases such as cancer.
When a cell divides, the genetic information is duplicated in a process known as replication name of DNA. To do so, a "replication machine is assembled on top of the DNA before duplication. A known protein complex under ORC recognizes DNA replication origin beginning of the process. Then, an enzyme, MCM2-7 helicase, whose role consists in unwinding and to separate the two strands of the DNA helix, is loaded onto DNA by the ORC system of the machine. The helicase is an enzyme-shaped ring composed of six subunits (hexamer), although how the ring structure opens and encircles the DNA, until now, remained a mystery.
initial theories in the field helicase assumed to exist in a conformation in open ring. Speck The team argued that this would probably lead to DNA replication poorly regulated without control or specificity. To examine the helicase activity in more detail at BNL Sun Jingchuan used an electron microscope and found, contrary to initial theories helicase actually existed as a closed conformation ring.
To determine where in the six subunits, the helicase opens to encompass DNA, the team generated links that blocked the opening at different positions cycle. They found that if they blocked a specific interface between MCM2 and MCM5, DNA could not enter. A small molecule called rapamycin brings together the links; a molecular switch may be used to control the entry of DNA to the MCM ring and subsequent DNA replication. "Both in the context of our in vitro and in vivo, we showed that the opening of the interface MCM2 / MCM5 helicase loading is essential for DNA," says Christian.
"The field has known for some time that DNA can pass through the ring MCM2-7, but was never sure MCM subunits are used for regulated helicase loading. by designing an elegant experience, Speck laboratory has now shown once and for all that the MCM2-5 is the only entry point for DNA, "says associate Huilin Li at BNL.
in eukaryotes, the helicase MCM2-7 hexamer form a double (with another unit MCM2-7) when loaded on the DNA. in this study, the group has also set the long-standing dispute over whether the helicase is actually loaded as one hexamer, which then dimerizes or is loaded as a dimer to the offset. They concluded that the helicase is actually loaded as one hexamer before forming a double hexamer.
in a successful collaboration that exploits the expertise of electron microscopy with BNL chemical biology and genetics expert at the MRC clinical sciences Centre, the study focuses on key issues describing the processes involved in DNA replication. "Our work is aimed at understanding the molecular mechanism of DNA replication at a fundamental level. Yet our findings could have important implications, perhaps pointing to new ways to fight against cancer, because the DNA duplication is a prime target for inhibiting the growth of cancer cells, "said Christian.
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