A clear picture of how the first responder is recruited to sites of DNA damage

A clear picture of how the first responder is recruited to sites of DNA damage ...

The particular sequence of As, Cs, Gs, and Ts in DNA provides information for the formation of an organism.

The fact that our DNA requires constant maintenance to keep it safe is not what we see here. If DNA was not for dedicated DNA repair equipment that routinely corrects errors, information would be quickly degraded.

Proteins that participate in the DNA damage checkpoint evaluate the cells DNA for mistakes and, if necessary, discontinue cell division and repair. When this checkpoint breaks down, which may occur as a result of genetic mutations DNA damage builds up, and the result is often cancer.

Though scientists have learned a lot about DNA damage and repair in the last 50 years, important issues remain. One particularly bedeviling puzzle is how a repair protein called the 9-1-1 clamp a DNA damage first responder attaches itself to the site of a broken DNA strand to activate the DNA damage checkpoint.

According to Dirk Remus, a molecular biologist at theSloan Kettering Institute (SKI), who studies the fundamentals of DNA replication and repair, this attachment is a crucial step. However, the mechanisms involved are absolutely unknown.

A clear picture of how the 9-1-1 clamp is recruited to DNA damage sites has emerged datorita a collaboration between the Dr. Remus lab and the of SKI structural biologist Ronard Hite. The results, which are unconcerned in the field, were published on March 21, 2022 in the journalNature Structural and Molecular Biology.

Surprising Results From Complementary Expertise

The startling discoveries grew out of a collaboration between two labs with complementary experience. Dr. Remus'' laboratory employs biochemical methods to investigate the process of DNA replication and repair. A primary objective of his research over the past several years has been to reconstitute the entire DNA replication-and-repair process in a test tube, apart from a surrounding cell.

A result of this work, his lab has purified several components of the repair equipment, including 9-1-1 proteins and proteins that facilitate the binding of 9-1-1 to DNA.

If these complexes could be viewed at anatomic resolution, then they would provide a set of freeze-frame images of the individual steps in the repair process. Thats when he turned to the Dr. Hites lab for assistance.

I said, "We have this complex; can you assist us in deciding whether or not it works? "He did it.

Dr. Hite, a structural biologist with extensive experience in using a technique calledcryo-electron microscopy (cryo-EM), which allows the study of proteins and protein assemblies by observing their fine-grain movements at resolutions that can reveal the positions of individual amino acids within the proteins. Much like the gears and levers of a machine, its these amino acids that enable proteins to serve as the cell''s workhorses.

Dr. Hite claims that many of the techniques that our lab has developed in the past few years were perfectly suited to answering this question. By combining these structures in a logical manner, we can come up with a suggestion for how this clamp works.

They did it, and the results were astounding.

According to Dr. Hite, the model developed had a variety of features that contradicted what was previously assumed to be the way these types of clamps are being loaded onto DNA.

A New Method for Opening and Closing a DNA Clamp Around DNA

The 9-1-1 clamp is shaped like a ring. It must open to allow the single-stranded DNA to reopen into the clamp''s center and then close around it. This is achieved by another protein complex called the clamp loader complex.

Prior to this, it was assumed that clamps would open in the manner of a lock washer, where basically the two open ends of the clamp would rotate out of plane to narrowen the gap, according to Dr. Remus. But this point suggests that the 9-1-1 clamp opens much more widely than previously, and it opens completely in plane theres no twisting as in the lock-washer scenario.

Scientists claim that the lock-washer technology has existed for over two decades and is the driving force behind the fabrication of a clamp around DNA. In this case, it is jeopardy.

Another surprise was that the 9-1-1 clamp loader complex was observed to bind DNA in the opposite direction from other clamp loader complexes that act on unamaged DNA during normal DNA replication. This observation explained how 9-1-1 is specifically recruited to locations of DNA damage.

From Basic to Translational Research

Dr. Remus believes that his research might be beneficial to cancer patients out of providing a satisfying answer to a fundamental biological puzzle.

Many current chemotherapy therapies work by interfering with DNA replication of cancer cells and generating the type of DNA damage that is normally fixed through repair processes created by the 9-1-1 clamp. Because cancer cells already have a reduced ability to repair DNA damage, the addition of DNA-damaging chemotherapy therapies can hinder the cells'' ability to fix their DNA, and so they die. (This is how drugs calledPARP inhibitorswork, for example.)

Scientists might possibly design drugs that interfere with this step of the repair process, making chemotherapy drugs even more effective.

One of the great things about working here at SKI is that a basic scientific research may be the foundation for translational research that ultimately results in improved outcomes, according to Dr. Hite.

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