Rensselaer Researchers Develop Tool to Detect
Low Levels of Sugars Produced by Living
Organisms
Tiny amounts of carbohydrates (1 |
Researchers at Rensselaer Polytechnic Institute have
developed an ultrasensitive method for detecting sugar
molecules — or glycans — coming from living organisms, a
breakthrough that will make possible a more detailed
understanding of cellular functions than either genetic or
proteomic (the study of proteins) information can provide. The
researchers hope the new technique will revolutionize the study
of glycans, which has been hampered by an inability to easily
detect and identify minute quantities of these molecules.
“The glycome is richer in information than the genome or the
proteome. A cancer cell, for example, might have the same
genome as a non-cancer cell, but it produces different sugars,”
said Robert Linhardt, the Ann and John H. Broadbent Jr. ’59
Senior Constellation Professor of Biocatalysis and Metabolic
Engineering at Rensselaer, and an author of the study. “Until
now, the stumbling block in glycomics has been rapid and
sensitive determination of the glycans present in a biological
sample, and up to now we were very limited by how much we could
detect. With this technique that we’ve developed, Glyco-qPCR,
we can detect a very small number of molecules and that should
accelerate the growth of the field.”
The new technique is discussed in a paper titled “Signal
Amplification by Glyco-qPCR for Ultrasensitive Detection of
Carbohydrates: Applications in Glycobiology,” which was
published in the Oct. 16 online edition of Angewandte
Chemie International. Linhardt and Jonathan Dordick,
director of the Rensselaer Center for Biotechnology and
Interdisciplinary Studies (CBIS), vice president for research,
and the Howard P. Isermann ’42 Professor of Chemical and
Biological Engineering, were joined in the research by Seok
Joon Kwon, Kyung Bok Lee, Kemal Solakyildirim, Sayaka Masuko,
Mellisa Ly, Fuming Zhang, and Lingyn Li.
Linhardt used the analogy of a house to explain the
importance of glycans in biology and the promise of glycomics
in medicine and biotechnology: If genes are the blueprints, and
proteins are the structure, than sugars—glycans—are the
decoration of all living matter. Just as dozens of houses in a
development—despite a shared blueprint and identical external
appearance—can have a unique interior identity based on wall
colors and furnishings, so can two cells share the same genome,
and similar proteome, but function very differently from one
another, Linhardt explained.
“You can look at a blueprint of a house and it can tell you
something about the house, but it certainly can’t tell you the
colors of the walls,” Linhardt said. “We’ve developed a method
to start to detect what the decorations will look like, and
that will give us an insight into what the house will
ultimately become.”
Linhardt said the technique is likely to find applications
in the study of all complex multisystem diseases, such as
cancer and diabetes.
“This gives us a new tool to study fundamental biology and
chemistry,” Linhardt said. “It allows us a higher resolution
view into the functions of a cell than the genome or proteome.
With this tool we can go inside a cell, poke around, and
understand how to predict the behavior of that cell and
ultimately control it.”
As the name of the new technique suggests, Glyco-qPCR is
built on Polymerase Chain Reaction (PCR), a technique, which
enabled fast and cost-effective sequencing of genetic
information, fueling a rapid expansion in genetics starting in
the mid-1980s.
PCR allows researchers to produce mass copies of a
particular sequence of DNA, or “amplify” the sequence, turning
one precious sample into a nearly limitless supply of a
particular sequence. The large sample makes it possible to
perform other techniques that determine the identity of the
particular sequence.
Glycans, the sugar molecules present in living cells, are
even smaller and more complex than DNA sequences, and
therefore, even more difficult to identify, Linhardt said.
Moreover, unlike DNA, they have proven resistant to
“amplification.” So the Linhardt team took another
approach.
The team has developed a technique for chemically attaching
a specific DNA sequence to a specific sugar molecule. The team
has built a catalogue of molecules that can be “tagged,” each
with a specific DNA sequence.
Once tagged, the team uses PCR to amplify the DNA tags,
allowing them to identify the tags — and therefore the glycans
— that are present, and the proportions in which they are
present, in a given sample.
“We don’t really detect the molecule, we detect the DNA
that’s attached to it,” Linhardt said. “The DNA tags are
cleverly designed so that they only attach to certain
molecules. We can then amplify the DNA, see what kind of DNA it
is, and then infer the molecule that it’s attached to.”
None of the currently used methods of glycan analysis, such
as mass spectrometry or high-performance liquid chromatography,
amplify the amount of sample that is present so they are much
less sensitive, Linhardt said. While these current methods are
capable of detecting a few billion glycan molecules, Glyco-qPCR
can detect a few hundred glycan molecules.
The development of PCR in 1983 put the study of genes within
reach of research labs around the world, unlocking the
potential for knowledge about how genes work and treatments
build on that knowledge. Linhardt hopes Glyco-qPCR will effect
a similar transformation.
“Although it is an indirect method that piggy-backs on
PCR, amplification technology like our Glyco-qPCR holds the
same promise for glycomics research,” Linhardt said. “I believe
that it is revolutionary for the fields of glycomics and
glycobiology.”
