A complete picture of protein unfolding and refolding in surfactants
CIC nanoGUNE Seminars
- Speaker
-
Daniel Otzen, Aarhus University
- When
-
2019/10/08
13:00 - Place
- nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
- Add to calendar
- iCal
Systems containing proteins and surfactants are of broad interest,
scientifically as well as technologically, owing to their widespread
application in detergency and various biotechnologies. It is by now well-
established (by our group and others) that the anionic surfactant SDS
denatures most globular proteins; furthermore, the end-point of the unfolding
reaction is a complex consisting of nearly intact SDS micelles with the
unfolded proteins wrapped around the micelles. The proteins' alpha-helical
secondary structure is either preserved from the native state or (more often)
induced by the interaction with the micelle. Recently, we have also shown that
addition of non-ionic surfactant to solutions with SDS-protein complexes leads
to refolding of the proteins and to regain of secondary structure also for
beta-sheet proteins.
While numerous studies, several of which from our own groups, have
investigated the unfolding and refolding processes at the level of the
protein, there is a major gap in our understanding: we simply do not know how
the surfactants and proteins cooperate or "dance together" to facilitate these
processes. The key question is as follows: What are the steps by which the
protein encounters the surfactant micelle (and vice versa) and how do they
both rearrange in response to the other component in order to lead to a new
state, either an unfolded protein-surfactant complex or - in the case of
refolding - a protein liberated from the "shackles" of the original denaturing
anionic micelle?
We present the first work which studies the kinetics of unfolding and
refolding of a protein as it interacts with surfactants, both from the
perspective of the protein and the surfactant. The key to this new
understanding is to exploit synchrotron radiation sources to record stopped-
flow Small Angle X-ray Scattering spectra at low-ms resolution of the evolving
protein-surfactant complexes. By combining this with stopped-flow circular
dichroism and tryptophan fluorescence we have for the first time obtained a
detailed picture of the protein and surfactant structures involved in each
step of the unfolding and refolding process. The combination of the techniques
has given unique information on the various steps, in the time scales and on
the involved intermediate structure. Our work reveals an intriguing sequence
of events: unfolding involves redistribution of the protein around the micelle
while refolding involves parallel detachment and refolding steps.
**Host:** A. Bittner