research team at SLAC National Accelerator Laboratory has been studying an
enzyme found in bacteria, plants, and some animals that repairs DNA damage
caused by UV rays from the sun. This enzyme is called DNA Photolyase. This
enzyme is thought to be a reason why plants are less susceptible to UV damage
than humans, despite the fact that they have continuous hours of sun exposure
throughout each day 1.
UV light from the sun can cause
considerable damage to DNA in a matter of seconds. These UV rays have the
ability to create hundreds of unwanted links within DNA’s double helix 1.
These links occur between atoms in the building block thymine. These additional
& unnecessary links make the DNA bulky and unrecognizable by DNA
replication tools. Cyclobutadipyrimidines, or pyrimidine dimers, are the major
DNA photoproducts produced by UV light. If left unrepaired, these dimers can
cause diseases like cancer, and death 2.
An experiment by Sancar et al. (1984)
purified the DNA photolyase enzyme in E.
coli in order to study its structure and function. They found that DNA
photolyase is a monomer with an apparent molecular weight of 49,000 2. It is
a flavoprotein with a noncovalent FAD moiety. The enzyme binds to
DNA-containing pyrimidine dimers in a light-independent step and converts these
dimers to pyrimidines upon exposure to UV light 2. In other words, DNA
photolyase is able to monomerize these dimers (or “cut out” thymine links) and
restore the biological activity of irradiated DNA, but only in the presence of
same sunlight that carries UV rays also carries blue light that activates DNA
In order to observe this enzyme at work,
SLAC laboratories have been using the Linac Coherent Light Source (LCLS), which
uses ultrabright and ultrafast pulses of an x-ray laser 1. This allows
researchers to “examine DNA photolyase at work as it catalyzes chemical
reaction in real time and at the atomic scale” 1. The researchers use LCLS to
activate DNA photolyase with a carefully controlled light pulse from a laser.
Then, they expose the enzyme to LCLS-generated x-ray pulses. The analysis of
x-ray data “reveals chemical and structural changes in the enzyme at the atomic
level,” thereby allowing researchers to witness chemical reactions “occurring
at a time scale of a millionth of a billionth of a second” 1.
LCLS allows researchers to capture a
series of high-resolution shots in sequence, thereby allowing them to watch the
enzyme work. This is especially helpful since photolyase is easily controlled, because
it simply needs to be exposed to light in order to be activated. Being able to
observe the enzyme function in real time is huge. This technology could potentially
help to engineer new enzymes and synthetic versions of already existing enzymes
that drive essential reactions in biological systems 1.