Significance of Knotted Structures for Function of Proteins and Nucleic Acids - September 17-21, 2014

Significance of Knotted Structures for Function of Proteins and Nucleic Acids

Poster Session II

29 – POS Board 1 Unbinding and Unfolding of Adhesion Protein Complexes in Stretching Simulations Bartosz Rózycki 1 , Lukasz Mioduszewski 2 , Marek Cieplak 1 . 2 University of Warsaw, Warsaw, Poland. 1 Polish Academy of Sciences, Warsaw, Poland, We made coarse-grained simulations to analyze mechanically induced dissociation and unfolding of the protein complex CD48-2B4. This heterodimer is an indispensable component of the immunological system: 2B4 is a receptor on natural killer cells whereas CD48 is expressed on surfaces of various immune cells. We find that the dissociation process strongly depends on the direction of pulling and may follow different pathways. When pulling with a constant speed, there are several force peaks before the subunits disconnect. In some pathways the final peak (from tensile forces involved in the act of separation) is lower than an earlier peak, associated with shear-involving unraveling of individual subunits (mainly CD48). These results suggest that measuring the highest force in AFM pulling experiments may not provide direct information about adhesion forces. In living cells both subunits are anchored in cell membranes by their C-terminal domains. Interestingly, pulling by the C-termini results in the simplest scenario, with only one force peak and no different pathways. On the contrary, pulling by the N-terminus of the CD48 subunit always results in two pathways, no matter which other terminus is being pulled. In constant force simulations, dissociation process changes if the pulling force exceeds the maximum force from constant speed simulations. Dependence of unfolding time on force is different in these two force regimes. In both constant speed and force simulations, the CD48-2B4 interface can be divided into three distinct patches that act as separate units when resisting the pulling forces. They may break simultaneously or separately, depending on the pathway and pulling direction. The simulation procedure was verified by simulating Synaptotagmin 1, a membrane-trafficking multidomain protein, which was also studied experimentally. Our simulation results agree with experimental findings.

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