Nonequilibrium, Single-Molecule Studies of Protein Unfolding Ching-Hwa Kiang, Rice University, DMR-0505814

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Nonequilibrium, Single-Molecule Studies of
Protein UnfoldingChing-Hwa Kiang, Rice
University, DMR-0505814
We used the atomic force microscope to manipulate
and unfold individual molecules of the titin I27
domain and reconstructed its free energy surface
using Jarzynski's equality. The free energy
surface for both the stretching and unfolding was
reconstructed using an exact formula that relates
the nonequilibrium work fluctuations to the
molecular free energy. The unfolding free
energy barrier, i.e. the activation energy, was
directly obtained from experimental data for the
first time. This work demonstrates that it is
now possible to obtain free energy surfaces for
molecular systems, including systems where only
nonequilibrium work can be measured. N. C.
Harris, Y. Song, and C.-H. Kiang, (2006)
submitted.
Stretching single protein molecules
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Nonequilibrium, Single-Molecule Studies of
Protein UnfoldingChing-Hwa Kiang, Rice
University, DMR-0505814

• The advance in nano-scale instrumentation has
  made it possible to manipulate and observe
  reactions at the single-molecule level. Seeing
  is believing has provided basis for proof of
  principles and gaining important insight into the
  complex biological world. We want to explore
  biological molecular properties and interactions
  using novel nano-tools such as atomic force
  microscope to study single bio-molecules.
  Knowledge of accurate thermodynamic properties of
  protein systems is important for biophysical and
  biochemical understandings of molecular
  processes, expanding understanding of biology and
  medicine under physiological conditions.
• The challenge lies on how to relate data from
  single-molecule measurements to fundamental and
  physiologically relevant properties. The biggest
  problem is that while manipulating the molecules,
  we have perturbed the system and forced it to
  undergo transitions through a non-equilibrium
  process. For example, in studying the heart
  muscle protein titin, we stretch the molecule
  faster than what happens during heart muscle
  contraction and relaxation. The first step is to
  determine the quantities at zero force limit.
  Application of the recently derived
  nonequilibrium work theorem to such problem
  should allow us to extract useful information
  that are not accessible with conventional
  methods.

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Nonequilibrium, Single-Molecule Studies of
Protein UnfoldingChing-Hwa Kiang, Rice
University, DMR-0505814
Education Four graduate (Nolan Harris, Eric
Botello, both minority, Yang Song, and Chad
Richard), two undergraduate (Jacob Sargent and
Casey Wang, female) and three postdoc (Dr.
Leiming Li, Dr. Wei Liao, and Dr. Fang-Chi Hsu,
female) worked on research supported by this NSF
Award. Students and postdoc background ranges
from physics, chemistry, to bioengineering,
making the research environment truly
multidisciplinary.
Social Impact Single-molecule manipulation and
measurements allow us to probe many complex
cellular assemblies and biological processes on a
nanometer scale. The mechanical properties of
biomolecules are functions underlying the
structures, and are crucial to many biological
processes. For example, mechanical properties of
muscle proteins, such as titin and dystrophin,
play an important role in muscle contraction, and
malfunction of the proteins have been directly
linked to many heart and muscular diseases. We
are developing a method that can be used as a
reliable technique to be used to determine a wide
range of fundamental biomolecular properties that
are important in understanding diseases.
Image http//www.oxford-personal-trainer.co.uk
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Nonequilibrium, Single-Molecule Studies of
Protein UnfoldingChing-Hwa Kiang, Rice
University, DMR-0505814

• The research project supported by NSF is
  interdisciplinary because it uses physical
  techniques to solve biological problems.
  Graduate and undergraduate students, as well as
  postdoctoral fellows were trained to use the
  state-of-the-art atomic force microscopy and
  spectroscopy techniques. The research group
  members came from different disciplines, ranging
  from physics, chemistry, to engineering.
  Interactions with the Texas Medical Center on a
  regular basis have made the multidisciplinary
  approach to science beneficial to my team members
  as they advance the field of biophysics at Rice
  and beyond.