Our research is
focused on proteins that self-assemble into hierarchical functional
structures. The main system we are currently working with is
Adiponectin Activity by Oligomerization:
Adiponectin is a
protein secreted exclusively by adipocytes. It is emerging as a key
player in regulating energy balance, and it’s misregulation is strongly
tied to Type II diabetes. Epidemiological studies have shown that
diabetics, obese people have abnormally low levels of adiponectin.
Adiponectin knockout mice are strongly susceptible to diet-induced
insulin resistance and administration of adiponectin increases insulin
found in the body in several forms, as a trimer, hexamer and a high
molecular weight species that is still poorly characterized.
Remarkably, the oligomeric state changes the tissue specificity and
activity of the protein. The trimer acts on muscle cells to stimulate
fatty acid oxidation; the hexamer can suppress hepatic glucose output.
Furthermore, thiazolidinediones, which are used to treat type II
diabetes, increase the ratio of high molecular weight complex relative
to the other species. Thus, it is important to obtain large quantities
of the high molecular weight form and characterize its oligomeric
state. This information will then be correlated with its biological
activity as we uncover it in collaboration with the Lodish Lab at the
We are currently
purifying all three forms from adipocytes. We will use spectroscopic
methods as well as analytical ultracentrifugation to characterize their
oligomeric state and secondary structure.
representation of adiponectin domain structure and oligomeric
state. Adiponectin has an N-terminal collagen domain followed by a
globular domain. The trimer is thought to be the basic building
block for higher oligomers.
Ribbon representation of the
trimeric globular domain of adiponectin. The globular domain of
adiponectin has a 10-stranded stranded jelly roll topology that is
structurally homologous to the TNF-a
family members. Interestingly, it self-assembles as a homotrimer
without the collagen domain. Each monomer is colored blue, green,
Cryoelectron micrographs of the trimeric (left),
hexameric (middle) and high molecular weight (right)
forms of adiponectin. Bar is
14.2 nm. From our publication in
J. Biol. Chem.,
278, 50810-50817 (2003).
Left. Equilibrium sedimentation trace of hexameric
adiponectin from E. coli. Right. .
Equilibrium sedimentation trace of trimeric adiponectin from E.
coli. The random residuals for both curves indicate that the
hexamer and trimer behave as ideal single species in solution and do
not equilibrate with alternate oligomers. From our publications in
J. Biol. Chem.,
278, 50810-50817 (2003) and
J. Biol. Chem.
277, 29359-29362 (2002).