Disordered Motifs and Domains in Cell Control - October 11-15, 2014

Disordered Motifs and Domains in Cell Control

Poster Session II

27-POS Board 3 From Chaos to Order: The Association Pathway of RNAse-S

Manuel Luitz , Rainer Bomblies, Martin Zacharias. Technical University of Munich, Garching, Germany.

Intrinsically disordered proteins can undergo transitions to ordered folded states upon association with a receptor protein. The transition pathway from unbound to bound complex is often difficult to determine experimentally. In case of the RNAse-S system a small S-peptide, disordered in the unbound state, forms an alpha-helical structure upon binding to the S-protein partner. The resulting complex forms an active RNAse-S enzyme. Molecular dynamics (MD) and advanced sampling approaches were used to investigate the coupled folding and binding of the S-peptide at atomic resolution. In agreement with xperiment significant conformational fluctuations of the isolated S-Peptide compatible with a disordered state were found. In order to identify residues which contribute most to the complex affinity and to find possible key contacts which are formed first on the route to the folded complex we performed in silico alanine scanning on the all residues of S-Peptide. Phe8 was identified as an anchor residue which contributes most to the binding free energy along with Met13 and His12 contributing slightly less to affinity. A pulling imulation on the centers of masses of S-peptide and S-Protein revealed an unfolding pathway with an initial opening of the S-Peptide helix followed by a subsequent dissociation of the key contacts. Based on these findings we could trigger complex formation in several extended MD simulations by closing the key contact of Phe8 with S-Protein and a disordered initial S-peptide. The subsequent S-peptide folding process resulted in helix folding emerging from a specific hydrogen bonding network to stabilize the final helical peptide structure. Comparison with coil-helix transitions of the S-peptide in solution allowed the characterization of important interactions with the S-protein that stabilize and promote helix folding.

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