Biomolecular recognition processes; the chemistry and biology of protein-saccharide interactions
group develops and implements synthetic methods that provide access to
biologically active compounds for hypothesis-driven and
discovery-driven research. This important foundation of our program
offers chemically-oriented researchers new opportunities to develop and
apply their synthetic skills. Biochemically- and biologically-oriented
researchers benefit from access to unique biologically active ligands.
Areas of current focus include:
synthesis of natural products and natural product-like structures;
diversity-oriented synthesis of ligands. The synthetic compounds are
used to explore cell surface receptor interactions, oligosaccharide
biosynthesis, carbohydrate recognition, and glycoconjugate function (1).
of new strategies for peptide/protein synthesis that provide access to
sequences with critical posttranslational modifications (e.g.,
glycosylation, tyrosine sulfation) that can be used to elucidate the
biological roles of these modifications (2). For a discussion of the rationale behind these projects, see: C&ENews.
of multivalent ligands (compounds displaying multiple binding epitopes)
that can be used to control receptor position. The synthetic ligands
facilitate the investigation of processes ranging from signal
transduction in chemotaxis to disarming proteins that mediate
inflammatory responses (3).
Biological Recognition Processes
use our synthetic ligands along with methods derived from fields
ranging from biochemistry to molecular and cell biology to biophysics
to investigate biological recognition processes and their consequences.
are especially interested in extracellular receptor-ligand interactions
and how they elicit/inhibit cellular responses. In addition to
exploring clustering cell-surface recognition events, we are
investigating protein aggregation processes, such as those that occur
in Alzheimer's Disease. A sampling of our current interests is listed
strategies for modulating carbohydrate - protein interactions in
inflammation. The selectins are a family of 3 cell surface proteins
(E-, P- and L-selectin) that participate in the recruitment of white
blood cells to sites of inflammation. Selectin function depends on
their interaction with carbohydrate epitopes. We have generated a
variety of synthetic ligands for L-selectin and used them to explore
selectin recognition and as templates for inhibitor design. We created
synthetic multivalent displays that bind to cell-surface L-selectin and
promote its proteolytic release from the cell (4 and 5).
Our current focus is on understanding the mechanism of L-selectin
downregulation. In addition, we are using diversity-oriented synthesis
to generate natural product-derived glycomimetics that inhibit the
have synthesized ligands that can selectively facilitate cell - cell
interactions. Such compounds may serve as new types of targeting agents
for the clearance and/or destruction of pathogenic cells (6).
collaboration with Regina Murphy's group, we have discovered agents
that interfere with fibril formation of the beta-amyloid protein, the
major protein component found in the plaques that occur in the brains
of Alzheimer's Disease (AD) patients. We are developing new methods to
identify agents that bind to beta-amyloid peptide. Our longterm goals
are to develop strategies to inhibit protein aggregation and to
generate agents that can be used to explore these deleterious events.
molecules on the cell surface, including membrane-associated proteins,
lipids, and carbohydrates, act as a remarkable conduit of information.
The resident cell-surface compounds have the critical role of reporting
to the interior on extracellular conditions (e.g., presence of
nutrients or toxins), so that the cell can respond appropriately. By
understanding how natural signaling processes are manipulated, we can
design synthetic ligands that can promote specific cellular responses.
estimates indicate that 1 in 5 people are infected with tuberculosis
(TB), and resistance to current treatments is growing. Because
mycobacteria (including those that cause tuberculosis or TB) require
galactofuranose residues to build their cell walls, compounds that
inhibit galactofuranose incorporation would serve as outstanding leads
for antimicrobial agents. We are investigating key enzymes involved
that mediate the incorporation of galactofuranose residues into cell
walls. The UDP-galactopyranose mutase is an intriguing enzyme involved
in generating UDP-galactofuranose, the requisite biosynthetic precursor.
galactopyranose mutase enzyme is fascinating because it requires a
reduced flavin co-factor to catalyze the interconversion of UDP
galactopyranose and UDP-galactofuranose (7).
We anticipate that the mechanism by which it catalyzes this
isomerization will be unprecedented. We have developed an expression
system that produces large quantities of this intriguing enzyme for
have developed an efficient synthesis of the UDP-galactofuranose and
its analogs. These compounds provide us with key reagents to study the
process of galactofuranose incorporation.
cellular responses can be elicited through a single receptor; thus, it
is not enough to identify a ligand that binds to or activates a
receptor to control its function. Evidence indicates that the position
of a receptor within the cell membrane can influence its function. We
are generating synthetic ligands that use non-covalent interactions to
organize receptors into different patterns on the cell surface (8).
We have found these ligands can reveal unique aspects of signaling
mechanisms, and we have focused initially on those that lead to
bacterial chemotaxis. We are especially interested in how bacteria can
respond to attractants with such high sensitivity (i.e., ca. 5% change
in concentration at 10 nM) over such a broad concentration range (i.e.,
5 orders of magnitude).
- Our results indicate that the cellular location of bacterial and archael chemoreceptors is conserved.
- We have used molecular modeling to design synthetic chemoattractants (9).
have found that the chemotactic responses of E. coli can be modulated
using ligands that cluster the chemoreceptors to different extents (10). Our studies suggest that bacteria can amplify and modulate
their signals by controlling the clustering of cell surface receptors.
Movies of bacterial movement in response to our compounds can be seen
by clicking on the Quicktime movie icons below.
findings have implications for regulating signaling processes in
bacteria, and we are pursuing this avenue for the design of new
are applying what we have learned from bacterial chemotaxis to
investigate the signaling processes that lead to antibody production
through the B cell receptor.
More detailed information can be found in our publications.
Quicktime is required to view the following movies, you may download a free version here.
100 mM 25mer