X-RAY RUNS: Apply for Beamtime
2017 Nov 1 - Dec 21
2018 Feb 7 - Apr 3
2018 Proposal/BTR deadline: 12/1/17
2018 Apr 11 - Jun 4
2018 Proposal/BTR deadline: 2/1/18
L. Pollack1, M.W. Tate1, N.C. Darnton2, J.B. Knight2, S.M. Gruner1,
W.A.Eaton3and R.H. Austin2
1Laboratory of Atomic and Solid State Physics, Cornell University
2Physics Department, Princeton University
3Laboratory of Chemical Physics, National Institutes of Health, Bethesda
MD
[Proc. Nat. Acad. Sci. in press]
Many questions are now being asked about the dynamics of large protein
molecules, including how they fold and move. The stability and folding
speed of a protein depend on the structures of the denatured as well as
the native state. Computer simulations suggest that slow folding amino
acid sequences collapse to compact structures with non-native topologies
before folding, while faster counterparts both collapse and fold
simultaneously.
To address questions about protein dynamics, a new technique has been
developed to aide measuring sub-millisecond time-dependent changes in
the conformation of large protein molecules. Proteins can be forced to
change conformational state using a solvent exchange technique, during
which proteins are subject to an abrupt change in the acidity of their
buffer solution. To achieve both rapid mixing and allow x-ray
measurements to study time-dependent changes, this group has
micro-fabricated a tiny 100-micron by 390-micron deep mixing device onto
a silicon wafer using the Cornell Nanofabrication Facility. Small-angle
x-ray scattering measurements inside the flow cell monitor the radius of
gyration of the macromolecules as a function of time before, during and
after solvent exchange. A recent experiment studied cytochrome-C as it
folds and unfolds in response to pH changes occurring at intermediate
time intervals of 150-500 microseconds. The results showed that the
protein first collapses to compact denatured structures before folding
very quickly to the native state.
Schematic of the nanofabricated flow cell used to
measure protein folding. The x-ray beam is moved along the output
flow to measure the protein shape at a variety of time intervals
after mixing.