DEPARTMENT OF
PHYSICAL CHEMISTRY
Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Special Seminar
Host: M. Sajadi

Monday, March 13, 2017, 11:00 am
All are invited to meet around 10:40 am for a chat with coffee & cookies.
Willstätter House, Faradayweg 10
Vasileios Balos
Liquid Dynamics group, Molecular Spectroscopy Department, MPI for Polymer Research, Mainz
Specific ion effects on protein fragments
The way ions interact with macromolecules and their aqueous environment is one of the most fundamental questions in solvation science, since the answer to this question can influence a variety of biotechnological and pharmaceutical applications. Until today, the fundamentals of our understanding of this kind of interactions originate from the seminal work of Hofmeister, who ordered the ions in the late 1800’s according to their efficiency to denature proteins. Despite the fact that his work triggered a huge amount of experimental and theoretical research, trying to elucidate the molecular mechanism that leads to the Hofmeister effect, a definite answer has not yet been given. In the present work we contribute to these efforts by giving definite answers to some of the most fundamental questions regarding the ion-protein interactions. More specifically, by using combination of Dielectric Relaxation Spectroscopy (DRS) and Terahertz Time-Domain Spectroscopy (THz-TDS), we studied and quantified the interaction of ions with protein fragments. We separately studied and quantified the effect both anions and cations on a single amide, which served as a model for the protein’s amide backbone. Our results indicated that the ion-amide interaction follows, in most of the cases, a direct Hofmeister effect. Moreover we demonstrated that both the anions and cations are able to interact with up-to- two amide moieties. Comparison between the interactions of an anion and a cation with an amide showed that the cation-amide interaction, for the strong denaturing agents of its series, is 2 times stronger than the interaction of the anions, which is surprising given that anions are in general more efficient in denaturing proteins. A notable exception of the previously described trend was found to be the guanidinium (Gdm+) cation. More specifically Gdm+, despite its demonstrated high denaturation tendency, showed an intermediate interaction strength compared with the effect of other denaturing cations (Li+ and Mg2+). Remarkably, the additivity of the the cationic and anionic effect is lifted for Gdm+ salts, an observation that contrasts our findings for salts consisting of small spherical ions. This notion points towards competing interaction sites between Gdm+ and the counter-anion In our work we demonstrate that direct interactions of ions with the amide backbone are playing a crucial role in the protein destabilization by salts. However, specifically for the Gdm+ cation we find strong evidence of additional alternative interaction sites.
Publications Covered: Quantifying transient interactions between amide groups and the guanidinium cation;. V. Balos, M. Bonn and J. Hunger, Phys. Chem. Chem. Phys., 2015, 17, 28539, and, Phys. Chem. Chem. Phys., 2016, 18, 1346 - Dissecting Hofmeister Effects: Direct Anion-Amide Interactions Are Weaker than Cation-Amide Binding; V. Balos, H. Kim,M. Bonn, and J. Hunger, Angew. Chem. Int. Ed., 2016, 55, 8125-8128 - Anionic and Cationic Hofmeister Effects Are Non-Additive for Guanidinium Salts. (nearly accepted)