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Download fileProtein Crystallization from a Preordered Metastable Intermediate Phase Followed by Real-Time Small-Angle Neutron Scattering
journal contribution
posted on 2021-10-29, 16:05 authored by Ralph Maier, Benedikt Sohmen, Stefano Da Vela, Olga Matsarskaia, Christian Beck, Ralf Schweins, Tilo Seydel, Fajun Zhang, Frank SchreiberWe present a systematic study using
real-time small-angle neutron
scattering (SANS) and optical microscopy to follow the protein crystallization
process in the presence of a metastable intermediate phase (MIP).
Using bovine β-lactoglobulin (BLG) in the presence of the divalent
salt CdCl2 as a model system, we first determine the experimental
phase behavior in D2O. The protein solutions become turbid
after crossing the first threshold salt concentration c*, and upon further increasing the salt concentration, the solutions
become less turbid but not completely clear again. Thus, the second
border is called pseudo-c**. Near pseudo-c**, crystallization follows a nonclassical process with
a MIP, which is further explored with a focus on the structural evolution
and the growth kinetics of the MIP prior to crystal nucleation. Real-time
SANS measurements show that a correlation peak develops inside the
MIP, and its peak position shifts to higher q-values
with time, finally stabilizing at a characteristic length scale of dMIP ≈ 84 Å. The area of this peak
(proportional to the amount of MIP in the sample) increases with time
first, reaches a maximum, and then decreases quickly upon crystallization
due to consumption by crystal growth. The evolution of the correlation
peak indicates a “preordering” nature of the MIP as
precursors of crystal nucleation, which lowers the nucleation barrier
for subsequent crystallization. These results of structural evolution
and the role of MIPs during a nonclassical crystallization process
may be relevant for other fields ranging from structural biology to
pharmacy.
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