The British Biophysical Society

British Biophysical Society Young Invesigators Award 2004

Mark Szczelkun

The BBS were once again pleased to see a good number of high quality candidates nominated for the BBS Medal. However, one candidate outshone the rest and the BBS were delighted to announce that Mark Szczelkun has been named as the BBS Young Investigator of 2004. Mark is currently a Wellcome Trust Senior Fellow at Bristol University.

David Trentham presents Mark with his Medal in Brighton.

Many science careers can be traced back to a particular topic that caught our youthful curiosity. "My original interest way back in school was DNA," explains Mark. The strength of Mark's interest in DNA has driven his career, which has encompassed a wide variety of approaches and techniques. It has all led to his award winning work - the development of a method that has allowed Mark to understand how certain enzymes move on DNA.

After finishing his biochemistry degree at Liverpool University, Mark started a PhD with Bernard Connolly at Southampton University looking at the nature of protein-DNA interactions using modified synthetic oligonucleotides. In 1994 he moved to Bristol where he was studying enzymes involved in DNA recombination events, until he saw a lecture by Steve Block. Block specialises in single molecule biophysics, and his lecture on the movement of polymerases along DNA captured Mark's imagination.

The fresh approaches being applied to polymerase seemed to offer Mark a chance to gain new information on restriction enzymes, some of which appeared to move along DNA. So he turned to some of the top single molecule biophysicists in the country: Justin Molloy and Mervyn Miles. Collaborations in place, Mark started a career development fellowship in 1998, looking at Type I and III restriction enzymes as molecular motors.

While restriction enzymes are a handy tool in molecular biology, their ability to motor along DNA might come as a surprise. But commercially available restriction enzymes used in molecular biology labs are Type II enzymes, and are not motor proteins. Type I enzymes on the other hand, one of the classes that Mark studies, are a far larger group of enzymes that contain motifs typical of DNA helicases. But while such motifs suggest that these enzymes move along DNA, Mark explains that there wasn't any clear proof, or a way to measure the translocation if it occurred.

So using a combination of fluorescence and stopped flow kinetics, and with help from Freddy Gutfreund and Tony Clarke at Bristol, Mark developed a novel technique to study motion in bulk solutions. Instead of measuring a single event like the single molecule biophysics methods, Mark measures the same event many times simultaneously and is able to measure motion on DNA independent of the mechanism of motion involved.

Mark's method can also be applied to other motor proteins because, as Mark puts it, he is only measuring how long it takes to get from A to B. And when almost 1% of the human genome is composed of helicases, there is a lot of motion to measure! Single molecule biophysics is now yielding results for these enzymes, allowing the two methods to be evaluated side by side. As Marks says of his rapid mixing technique, "It compares very nicely." Both methods give the same general kinetic rates for the Type I restriction enzymes.

Once Mark had a method to study the motion of restriction enzymes, he was then able to start analysing fine details. "Biophysics is an excellent means by which we can answer biological questions... we know an awful lot more now than we did 5 years ago," he comments. One of the advantages of the rapid mixing method is that Mark can now break down a specific problem into individual steps. "We can follow processes in terms of the DNA," he explains, allowing him to look aspects such as how fast the enzyme binds to the DNA, and what the chances are of the enzyme falling off, for example.

Mark is also looking at which strand of DNA the enzymes walk along, whether they prefer to travel in a particular direction, and what happens if there is a break in the DNA. It turns out, surprisingly, that these molecular motors are surprisingly insensitive to breaks. "It is remarkable how good they are at walking on DNA," comments Mark. But then these restriction enzymes are a little unusual in terms of motor proteins. In general they will walk along thousands of base pairs, while many other motor proteins only walk for a short distance before falling off.

So what's next? "Measuring rates is all well and good," says Mark, "but the aim is to understand their mechanisms." While it is now known that the helicase motif is responsible for these restriction enzymes motoring along DNA, their catalytic properties reside in a different part of the enzyme. Currently there are no 3D structures available for these classes of enzymes and Mark feels that the structural information is the next key step in understanding the mechanism of these enzymes.

Finally, what are Mark's thoughts about receiving the BBS Medal? "It's nice to know your peers think you are doing the right thing!" he jokes. On a more serious note, Mark feels it is important for biophysics to get the recognition it deserves. And that's certainly something the BBS agree with.

Mark received his BBS Medal at the Response to DNA Damage: Insights from Chemical, Biological, Structural Biology and Cellular Studies meeting at the University of Sussex which took place between 19-21 September. He presented a lecture entitled "A molecular motor that introduces double strand breaks into DNA".