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Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS I22-Small angle scattering & Diffraction	Impact of macromolecular crowding and compression on protein–protein interactions and liquid–liquid phase separation phenomena Karin Julius , Jonathan Weine , Mimi Gao , Jan Latarius , Mirko Elbers , Michael Paulus , Metin Tolan , Roland Winter Macromolecules DOI: 10.1021/acs.macromol.8b02476 Show Abstract ▼ Abstract: We determined the intermolecular interaction potential, V(r), of dense lysozyme solutions, which governs the spatial distribution of the protein molecules and the location of its liquid–liquid phase separation (LLPS) region, in various crowding environments applying small-angle X-ray scattering in combination with liquid-state theory. We explored the effect of polyethylene glycol (PEG) on V(r) and the protein’s phase behavior over a wide range of temperatures and pressures, crossing from the dilute to the semidilute polymer regime, thereby mimicking all crowding scenarios encountered in the heterogeneous biological cell. V(r) and hence the protein–protein distances and the phase boundary of the LLPS region strongly depend on the polymer-to-protein size ratio and the polymer concentration. The strongest effect is observed for small-sized PEG molecules, leading to a marked decrease of the mean intermolecular spacing of the protein molecules with increasing crowder concentration. The effect levels off at intermolecular distances where the proteins’ second hydration shells start to penetrate each other. Strong repulsive forces like hydration-shell repulsion and/or soft enthalpic protein-PEG interactions must be operative at short distances which stabilize the protein against depletion-induced aggregation, also at pressures as high as encountered in the deep sea, where pressures up to the kbar-level are encountered.	Feb 2019
I22-Small angle scattering & Diffraction	On the Origin of Microtubules’ High-Pressure Sensitivity Mimi Gao , Melanie Berghaus , Simone Möbitz , Vitor Schuabb , Nelli Erwin , Marius Herzog , Karin Julius , Christian Sternemann , Roland Winter Biophysical Journal 114, 1080 - 1090 DOI: 10.1016/j.bpj.2018.01.021 Diamond Proposal Number(s): [14949] Show Abstract ▼ Abstract: For over 50 years, it has been known that the mitosis of eukaryotic cells is inhibited already at high hydrostatic pressure conditions of 30 MPa. This effect has been attributed to the disorganization of microtubules, the main component of the spindle apparatus. However, the structural details of the depolymerization and the origin of the pressure sensitivity have remained elusive. It has also been a puzzle how complex organisms could still successfully inhabit extreme high-pressure environments such as those encountered in the depth of oceans. We studied the pressure stability of microtubules at different structural levels and for distinct dynamic states using high-pressure Fourier-transform infrared spectroscopy and Synchrotron small-angle x-ray scattering. We show that microtubules are hardly stable under abyssal conditions, where pressures up to 100 MPa are reached. This high-pressure sensitivity can be mainly attributed to the internal voids and packing defects in the microtubules. In particular, we show that lateral and longitudinal contacts feature different pressure stabilities, and they define also the pressure stability of tubulin bundles. The intactness of both contact types is necessary for the functionality of microtubules in vivo. Despite being known to dynamically stabilize microtubules and prevent their depolymerization, we found that the anti-cancer drug taxol and the accessory protein MAP2c decrease the pressure stability of microtubule protofilaments. Moreover, we demonstrate that the cellular environment itself is a crowded place and accessory proteins can increase the pressure stability of microtubules and accelerate their otherwise highly pressure-sensitive de novo formation.	Mar 2018
I22-Small angle scattering & Diffraction	Water-mediated protein-protein interactions at high pressures are controlled by a deep-sea osmolyte Karin Julius , Jonathan Weine , Melanie Berghaus , Nico König , Mimi Gao , Jan Latarius , Michael Paulus , Martin A. Schroer , Metin Tolan , Roland Winter Physical Review Letters 121 DOI: 10.1103/PhysRevLett.121.038101 Diamond Proposal Number(s): [14949] Show Abstract ▼ Abstract: The influence of natural cosolvent mixtures on the pressure-dependent structure and protein-protein interaction potential of dense protein solutions is studied and analyzed using small-angle X-ray scattering in combination with a liquid-state theoretical approach. The deep-sea osmolyte trimethylamine-N-oxide is shown to play a crucial and singular role in its ability to not only guarantee sustainability of the native protein’s folded state under harsh environmental conditions, but it also controls water-mediated intermolecular interactions at high pressure, thereby preventing contact formation and hence aggregation of proteins.	Jul 2018

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