Newswise — STONY BROOK, NY, December 14, 2022 — Every time a cell divides, the genome needs to be precisely duplicated to ensure that each new cell has a complete set of genetic instructions. This crucial process, known as DNA replication, requires a sophisticated molecular machinery that can unwind the double-stranded DNA, separate the two strands, and copy each one to produce two identical copies of the original DNA molecule.
One of the key proteins involved in DNA replication is the replicative helicase, an enzyme that acts like a molecular motor to unwind the DNA double helix. Understanding the structure and mechanism of helicases is essential for unraveling the complexities of DNA replication and for identifying potential targets for therapeutic intervention in various diseases, such as cancer and viral infections.
In a recent study published in the journal Nature Structural & Molecular Biology, a team of scientists from Stony Brook University and the University of Massachusetts Medical School, led by Professors Stephen Leffak and James Berger, has made significant progress in understanding how the replicative helicase operates. Using advanced cryo-electron microscopy (cryo-EM), they determined the high-resolution structure of the replicative helicase from _Bacillus subtilis_ in complex with a DNA substrate.
The structure reveals that the helicase has a unique "crab claw" shape, with two domains that come together to grip the DNA and separate the two strands. The crab claw conformation allows the helicase to encircle the DNA substrate, providing a stable platform for unwinding the double helix.
"This structure provides a clear picture of how the helicase binds and unwinds the DNA," said Stephen Leffak, Professor in the Department of Biochemistry and Cell Biology at Stony Brook University. "This is an important step towards understanding how the replicative helicase works and how it could be targeted for therapeutic intervention."
Additionally, the researchers identified a key regulatory mechanism that controls the helicase activity. They showed that the helicase can adopt two distinct conformations, an "open" conformation that allows it to bind to the DNA and an "autoinhibited" conformation that keeps the helicase inactive. The switch between these two conformations is controlled by a small regulatory protein called the single-stranded DNA-binding protein (SSB).
"The autoinhibited conformation acts like a safety mechanism that prevents the helicase from unwinding the DNA prematurely," explained James Berger, Professor of Biochemistry and Molecular Pharmacology at the University of Massachusetts Medical School. "The SSB protein acts as a key that unlocks the helicase, allowing it to bind to the DNA and start the replication process."
These findings provide new insights into the molecular mechanisms of DNA replication and reveal potential targets for the development of novel drugs that could inhibit helicase activity and interfere with DNA replication in pathogenic microorganisms or cancer cells.
The research team is now working to further investigate the structure and function of the replicative helicase and to understand how it interacts with other proteins involved in DNA replication. This research could lead to the development of new therapeutic strategies for treating diseases associated with DNA replication defects or dysregulation.
About Stony Brook University
Stony Brook University is a SUNY-operated public research university with more than 26,000 students and 2,700 faculty members. The University offers more than 200 undergraduate and 100 graduate degree programs in a wide range of disciplines, including the health sciences, engineering, business, social sciences, and humanities. Stony Brook's state-of-the-art facilities include the Stony Brook Southampton Marine Science Center, the Institute for Advanced Computational Science, and the Laufer Center for Physical and Biological Sciences. The University is a member of the prestigious Association of American Universities and is recognized for its excellence in research and education.
