Disordered Motifs and Domains in Cell Control Wednesday Speaker Abstracts
The C-Terminal Domain of Hepatitis B Virus Capsid Protein has Mastered being a
Jack-of-all-trades
Brian Bothner
1
, Navid Movahed
1
, Ravi Kant
1
, Jonathan Hilmer
1
, Adam Zlotnick
2
1
Department of Chemistry and Biochemistry, Montana State University. Bozeman, MT.
2
Department of Molecular & Cellular Biochemistry, Indiana University. Bloomington, IN
Hepatitis B Virus (HBV) is a serious human pathogen: 350 million people suffer from chronic
HBV infection and 600,000 die from it annually. Assembly of a HBV virion begins with
formation of an RNA-filled T4 icosahedral capsid. Using moves akin to a contortionist, the
circular dsDNA genome of the mature virus is reverse transcribed within the confines of the
capsid. Extensive structural, biophysical, and cellular characterization have revealed that the
capsid protein takes an active part in assembly, recruitment of the viral polymerase, the process
of reverse-transcription, and intracellular trafficking. Functional analysis of HBV core particles
has associated these biological roles directly with the C-terminus of the capsid protein. In an
interesting twist, one set of functions require the C-terminus to be on the exterior of the capsid,
while other functions place this domain on the interior. The 34 amino acid C-terminal domain is
rich in arginine residues, is subject to phosphorylation, and contains a nuclear localization signal.
Our work is being conducted using a series of mutant forms of capsid protein and a variety of
biophysical techniques including hydrogen-deuterium exchange mass spectrometry. We have
shown that the C-terminal domain reversibly unfolds leading to transient externalization.
Phosphorylation of this linear motif can initiate reorganization of packaged nucleic acid and
alters protein dynamics of the particle. The nucleoprotein core of HBV capsids is a complex
machine controlled by a multifunctional linear domain that interacts with nucleic acids, kinases,
and transport proteins all in days work.
Single-Molecule Biophysics of Proteins Disordered and Misfolding
Ashok Deniz.
The Scripps Research Institute, USA
Intrinsic Protein Disorder is increasingly recognized as a functionally important and prevalent
feature in biology. The special biophysics and chemistry of disordered protein motifs are
believed to play a key role in protein biology, function and misfunction in the cell. However, the
structural complexity inherent in these systems often limits the biophysical information available
from many conventional ensemble methods. We adapt and devise novel and state-of-the-art
single-molecule fluorescence methods with unique capabilities to uncover hidden structural and
kinetic information about such complex systems, by minimizing the averaging intrinsic to
ensemble techniques. We will discuss examples of our single-molecule studies which uncover
new details of the complex landscapes for disordered protein association and folding, features
that relate to their function and misfunction. Overall, we will highlight some of the unique
capabilities of single-molecule methods to map dynamic structural complexity in such systems,
thus providing insight critical to a fundamental understanding of biology.
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