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Seminar by Jun-Prof. Simon Ebbinghaus

Ruhr-University Bochum (Germany)

27 Nov 2015 11:00
27 Nov 2015 12:00
Lecture room 2009, Jülich GRS building (16.15)

Biomolecules function in the densely crowded and highly heterogeneous cell, which is filled up to a volume of 40 % with macromolecules [1]. Often, artificial macromolecular crowding agents are used to mimic these conditions in vitro and the excluded volume theory is applied to explain the observed effects [2]. However, recent studies emphasize the role of further contributions aside from a pure volume effect including enthalpic and solvent effects [3, 4]. We study cosolute effects at high molecular and macromolecular concentrations via a thermodynamic analysis of the thermal unfolding of ubiquitin in the presence of different concentrations of cosolutes (glucose, dextran, polyethylene glycol, potassium chloride) [5]. In contrast to the excluded volume theory, we observed enthalpic stabilization and entropic destabilization forces for all tested cosolutes. The enthalpic stabilization mechanism of ubiquitin in macromolecular polysaccharide solutions of dextran was thereby similar to the effects observed in monomeric glucose.

Further, it remains unclear how such cosolutes reflect the physicochemical properties of the complex cell environment as a characterization of the in-cell crowding effect is lacking. Thus, we developed a FRET-based macromolecular crowding sensor to study the crowding effect in living cells [6]. The averaged conformation of the sensor is similar to dilute aqueous buffer and cell lysate. We find that the in-cell crowding effect is distributed heterogeneously and can change significantly upon osmotic stress. The presented method allows to systematically study in-cell crowding effects and understand them as a modulator of biomolecular function.


[1] S. Zimmerman, S. Trach, J. Mol. Biol. 1991, 222, 599-620.
[2] H.-X. Zhou, G. Rivas, A. Minton, Annu. Rev. Biophys. 2008, 37, 375-397.
[3] Y. Wang et al., The Journal of the American Chemical Society, 2012, 134, 16614-16618.
[4] R. Gilman-Politi and D. Harries, Journal of Chemical Theory and Computation, 2011, 7, 3816-3828.
[5] M. Senske, L. Tork, B. Born, M. Havenith, C. Herrmann, S. Ebbinghaus, J. Am. Chem. Soc. 2014, 136, 9036-9041.
[6] D. Gnutt, M. Gao, O. Brylski, M. Heyden, S. Ebbinghaus, Angew. Chem Int. Ed. 2015, 54(8):2548–51, 2015.