Project Summary/Abstract
Membrane proteins represent approximately 30% of all known proteins but only
approximately 1% of all solved protein structures. Despite recent advances in methods for
membrane protein structural biology, knowledge about this important class of proteins lags behind
their soluble counterparts. Membrane proteins are critical to numerous aspects of health, ranging
from regulation cellular function and transport into and out of the cell, through to viral infections
which use membrane proteins as part of the infection cycle. Understanding the structure of
membrane proteins can be critical to disrupting such viral infections, and can also lead to the
development of effective antiviral therapies. In almost 90% of newly developed and approved
therapeutics, protein structural information was used to guide the development of the therapeutic
molecules. Due to the limited and incomplete structural information on membrane bound proteins,
the development of therapeutics and treatments that target membrane bound proteins is limited.
A significant contribution to the challenges in elucidating membrane protein structures is the lack
of robust and appropriate lipid membrane mimetics. Existing membrane mimetics introduce
notable challenges that limit membrane protein structural determination. These challenges range
from highly curved micelles which may not represent the essentially flat lipid bilayer, lack of
compatibility with many lipids for bicelles, large sizes of vesicles which introduces anisotropy, cost
and potential background signal from membrane scaffold proteins, and lack of control over
polymer structure and the presence of aromatic groups on several existing nanodisc forming
polymers. This highlights an urgent need to develop lipid membrane mimetics which both provide
a good approximation to the native lipid bilayer in terms of both structure and curvature, while
also facilitating structural analysis of the membrane protein embedded in the mimetic. Yet polymer
structure-function relationships are not well established for polymers that interact with lipids and
membrane proteins.
This project will use modern controlled polymer chemistry tools, to create a new class of polymers
that will self-assemble with lipids. These self assembled polymer-lipid systems will form well
defined discs on the order of 10s of nanometers, giving lipid membrane mimetics suitable for the
analysis of many membrane proteins. The advanced polymer chemistry techniques will enable
fine tuning of polymer’s length, charges, and hydrophobicity. Polymers will also be modified with
spin-labels for electron paramagnetic resonance spectroscopy, a magnetic resonance method.
The magnetic resonance spectroscopic methods will be used on polymers, lipids and membrane
proteins modified with appropriate spin labels, providing insights into the local dynamics and
proximities of the self assembled polymer-lipid and polymer-lipid-membrane protein complexes.
The information regarding the structure and dynamics of the self-assembled complexes across
the diverse range of polymer functionality and structures used will give important insights into how
polymer structure impacts its interactions and assembly with biological molecules. These insights
can be used to guide the design of polymers for robust lipid membrane mimetics.
Training and mentoring of undergraduate students as well as a graduate assistant will be a core
feature of the proposed project. A diverse team of students will work on all aspects of the project,
gaining skills from the fundamental polymer chemistry, magnetic resonance spectroscopy to
membrane protein biophysics. Undergraduate students will be integrated fully into the projects,
along with the graduate student, gaining skills in this field at the interface of materials science and
biophysics. Beyond core scientific training, students will gain written and oral communication skills
disseminating the results of the research.
