Significance of Knotted Structures for Function of Proteins and Nucleic Acids
Poster Session II
56 – POS
Board 28
Full Characterization of the Native State Dynamics of the Pierced Lasso Bundle Leptin
1
Ellinor Haglund
,
2
Brian Fuglestad,
3
Jeffrey K. Noel,
3
José N. Onuchic &
4
Patricia A. Jennings
1
Center for Theoretical Biological Physics (CTBP) and department of physics, University of
California at San Diego (UCSD), La Jolla, CA USA.
2
Department of Biochemistry and
Biophysics, University of Pennsylvania, Philadelphia, PA, USA.
3
Center for Theoretical
Biological Physics at Rice and UCSD (CTBP) and department of Physics, Rice University,
Houston, TX USA.
4
Departments of Chemistry and Biochemistry, University of California at
San Diego (UCSD), La Jolla, CA USA
Recently, we discovered a new structural complexity in the pleiotropic hormone leptin, where
the C-terminal disulphide bridge creates a covalent-loop through which part of the polypeptide
chain is threaded (as seen in knotted proteins, Figure bellow). We explored whether other
proteins contain a similar intriguing knot-like structure as in leptin and discovered 11 structural
homologous proteins in the PDB forming a new class of knot-like proteins. We call this new
helical family class the Pierced Lasso Bundle (PLB). Structure based models showed that the
dynamics of the native state are altered through oxidation, where the dynamics of the threaded
state is more malleable then the unthreaded state, suggesting a mode of controlling receptor
interaction and biological activity. To further investigate the malleable behavior of the PLBs we
used relaxation/dispersion NMR experiments together with MD structure based models and
explicit solvent simulations to fully understand the NSD of leptin. The results show increased
dynamics in the covalent-loop controlling the threaded topology as well as in one of the receptor
interphases engaging the second receptor to form the active quaternary receptor-ligand complex.
Finally, complete comprehension of the native state of leptin and its complex topology can
significantly influence
ab initio
predictions of newly identified protein targets as well as guide
therapeutic research and drug design.
Figure.
A cartoon representation of leptin. The front and top view of the protein in a cartoon
representation, where the two cysteines are highlighted in yellow. Helix A through D are part of
the four helix bundle while helix 4’ is outside the bundle in loop 4. Under oxidizing conditions
the cysteines forms a disulphide bridge creating a 50 residue long covalent-loop/lasso (blue).
Examining the structure lead to the discovery of a threaded topology where helix C and half of
helix B are threaded through the lasso creating a Pierced Lasso Bundle topology. The right panel
shows a schematic figure of the top view colored in the same manner as the cartoon
representation.
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