Hung-Jen Wu Research Lab
Chemical Engineering, Texas A&M University
Research
1.
Multivalent lectin binding & bacterial adhesion to host cell membranes
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Figure 1 Multivalent binding on cell membranes |
Glycans expressed on cell surfaces mediate
a wide range of biological processes, such as pathogen (e.g.
bacterial, viral) and exotoxin adhesion to host cells. Interestingly, a single
glycan-protein interaction is often weak; most proteins bind to glycans via
multivalent interactions, in which multiple binding domains in a single protein
simultaneously interact with multiple glycan molecules. Glycan receptors on
cell membranes are often mobile; glycans attached to lipids or membrane
proteins can freely diffuse and rotate on 2D fluidic cell membranes,
self-organizing to reach multivalent interactions with a protein. Such
multivalency leads to higher binding avidity and specificity, and is one of the
major recognition principles in many biological systems.
We recently monitored the hetero-multivalent binding
process of Cholera Toxin Subunit B (CTB) (i.e. a CTB
simultaneously binding to two or more different types of glycolipid receptors).
Surprisingly, when a very weak receptor (e.g. GM2) was
mixed with the strong binding receptor (e.g. GM1), GM1 activated the
interactions between CTB and GM2, enhancing the overall CTB attachment. We
demonstrated that the activation of low-affinity receptors was mediated via a
simple chemistry mechanism, Reduction
of Dimensionality (RD). (see
Figure 2) After CTB attaching to the first receptor, the subsequent binding
events are confined in a two dimensional membrane surface. Due to the reduced
dimensionality of diffusion, the effective concentrations of weak receptors
dramatically increase for the subsequent binding events; therefore, a weak
receptor can contribute to CTB binding.
The RD mechanism strongly depends on cell membrane dynamics. This
presents an issue to conventional ligand-receptor screening assays (e.g. microarray technology, ELISA, etc.) because these tools
that often immobilize receptors on solid surfaces miss the inherent membrane
dynamics. To date, no theoretical model is available to describe the
fundamental RD process. My research group is developing novel sensing
technologies and computation tools to investigate the RD mechanism and
understand the influence of hetero-multivalency in the pathogenesis of bacteria
(e.g. Pseudomonas
aeruginosa and Mycobacterium
tuberculosis).
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2.
Design targeted drug delivery systems using hetero-multivalent binding
principle
Inspired by the nature of bacterial
adhesion to host cells via hetero-multivalent binding, we discovered previously
unknown molecules from eukaryotic cells that mediate Pseudomonas aeruginosa adhesion. We decorated these new ligands on
the surface of the liposomal carrier to achieve targeted drug delivery. The
hetero-multivalent binding strategy, that is incorporation of different types
of targeting ligands on a liposome to simultaneously bind with different types
of receptors on a bacterium, significantly enhance drug retention at the
infection site. In addition to P.
aeruginosa, we used the same principle to design new targeted drug delivery
system for combating M. tuberculosis.
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Figure 3 Survival of thigh infected mice
treated with monovalent targeted liposomes and hetero-multivalent targeted
liposomes. The mice
treated with hetero-multivalent targeted liposomal ciprofloxacin have a
significantly higher survival rate than those treated with LacCer-only or Gb3-only liposomal ciprofloxacin. |
3.
Machine learning and Surface Enhanced Raman Spectroscopy (SERS) for chemical
and biological sensor
To improve sensing sensitivity and
specificity, we have developed a multi-functional “Nanopaper”
that offers analyte collection, analyte separation, and Raman signal
enhancement. Nanopaper is a silver coated glass
microfiber filter paper. The amplified local electromagnetic field near
nanostructured silver surfaces could enhance Raman signals by at least five
orders of magnitude. Such a phenomenon, called Surface-enhanced Raman
Spectroscopy (SERS), is an effective tool for detecting dilute analytes. In
addition to signal enhancement, this nanopaper can
serve as a stationary phase in paper chromatography (PC). As the number of
analytes in a sample increases, Raman peaks are more
likely to overlap, confounding features. Separating analytes before detection
is an effective approach to reduce spectral overlaps. Our nanopaper
combines Paper Chromatography and SERS (PC-SERS) in a single substrate,
allowing end users to rapidly and accurately detect glycan, food ingredients,
and illicit substances. Moreover, to process the complex Raman spectra, we
integrated machine learning classification and regression to profile glycan
molecules in complex biological samples.
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Figure 4 Nanopaper for PC-SERS detection. The paper chromatography
separation simplified the SERS identification of mixed analytes. The
low-cost, disposable, and portable nanopaper can
serve as a versatile technique for the identification of chemical and
biological compounds within complex matrices. |
4.
Multifunctional nanomaterials for biosensing
My research group focuses on developing highly
structured nanomaterials for biosensing. We have established the novel
instruments to quantitatively explore various biological processes, including nanocube-based lipid bilayer array, multiplexing chemical
and biological Raman sensors, and Nanotrap for
infectious disease screening.
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Figure 5 Nanocube-based
Lipid Bilayer Array. Silica-coated silver nanocubes are covered
by supported fluidic lipid bilayers where receptors are presented. Binding
kinetics were detected by monitoring absorption spectra with standard
microplate reader |
