To understand that, imagine a relay team at a track meet, with one
member of the team after another advancing the baton and passing it
along to the next as they move toward the finish line. Enzymes do some
of their work that way within cells, working as catalysts to speed up
reactions and pass that new product along to the next enzyme. In this
case, the “batons” are the products of these reactions, changing between
each handoff. So enzyme No. 1 modifies the baton and hands it off to
enzyme No. 2, which modifies the baton and hands it off to enzyme No. 3
and so on until the desired product is achieved.
“Imagine that you want to pass a product along to the next person,”
Chen said. “But you are so far apart that it’s hard to pass it on. If
you reduce the distance between the different partners, you get better
efficiency and accuracy and you reduce competition.”
In nature, enzymes often gather in groups to do this collaborative
work in closer proximity, using protein-based scaffolds as their
gathering place and producing a “cascade” of biochemical reactions that
Chen and Berckman have found an improved way to control the
construction and placement of those scaffolds, as well as the cascade of
reactions they produce, using the revolutionary new genetic technology
known as CRISPR/Cas9.
CRISPR is an acronym (clustered, regularly interspaced palindromic
repeats) that describes DNA sequences used in the immune system of
certain bacterial cells. When the bacterial cell is attacked by a virus,
it clips off a bit of the virus’s DNA and stores it, using that
information to recognize and destroy the attacker the next time it comes
The process includes a protein called Cas9, which binds itself to the
targeted segment of DNA and cuts it at that spot. Geneticists are now
able to use that process to edit the genetic code to remove mutations
that cause disease or other dysfunction.
Chen and Berckman aren’t editing genetic code with CRISPR. They
are using a modified form of Cas9, called dCas9, which does not have
that scissor-like ability but does act as a “super binder.” It holds
fast to any targeted DNA sequence and allows for precise placement of
these enzyme scaffolds and their cascade of reactions.
Chen already has used dCas9 for gene regulation and imaging applications. This is a new application.
Guided in its work by RNA, the technique allows for an increased
number of fusion points and a necessary unlocking mechanism called
“toehold gRNA,” increasing both precision, efficiency and
“We’ve made a more accurate assembly line,” Berckman said. “We can
turn it on, now we have to be able to turn it off. Then, ultimately, you
could apply this to as many pathways as you can think of —
pharmaceuticals, biofuels, cancer therapies.”
To learn more about CRISPR and the new UD research, view this animated video.
Article by Beth Miller; photo by Evan Krape; animation by Jeffrey C. Chase
Published Nov. 14, 2019