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Polymers and Self Assembly: From Biology to Nanomaterials
Monday Speaker Abstracts
Cryo-EM of Helical Polymers
Edward Egelman
University of Virginia, USA
Cryo-EM has undergone a revolution, driven by direct electron detectors, and a near-atomic level
of resolution can now be reached for many biological samples. While complexes such as the
ribosome can be solved at higher resolution and more readily by cryo-EM than they can be by
crystallography, they can still be crystallized. However, a vast number of complexes of
biological interest are helical polymers, and most of these can never be crystallized. I will
describe the application of cryo-EM to helical assemblies in four different areas: 1) Vibrio
cholera, the organism responsible for cholera, uses a Type Six Secretion System in pathogenesis.
We now understand in detail how parts of this system assemble and work. 2) Type IV pili are
essential for the infectivity of bugs such as Neisseria meningitidis. We have shown for
Campylobacter jejuni (responsible for most food-borne illnesses in the world) that the conserved
flagellin protein can be assembled into different quaternary structures by small amino acid
changes. We show the same thing for Type IV pilins. 3) Flexible filamentous plant viruses are
responsible for half of the viral agricultural crop damage, but have resisted all attempts at
structure determination since the studies of J.D. Bernal >75 years ago. We have solved the
structure of two members of this family, bamboo mosaic virus (BaMV) and wheat streak mosaic
virus (WSMV) and show how, because they are completely non-toxic, they can be used in
biotechnology, in everything from medical imaging to serving as platforms for vaccines. 4)
Viruses that infect hyperthermophilic archaea can survive in nearly boiling acid or organic
solvents. We now understand how the stability of DNA in SIRV2 and AFV1 is achieved. AFV1,
like Ebola, is a filamentous membrane-enveloped virus, and we present the first atomic structure
of such a virus.