Conformational Ensembles from Experimental Data and Computer Simulations

Conformational Ensembles from Experimental Data and Computer Simulations

Poster Abstracts

87-POS Board 7 Large, Dynamic, Multi-protein Complexes - Molecular Simulations and SAXS Experiments Bartosz Rozycki . n/a, Warsaw, Maryland, Poland. Many biological functions are carried out by large and dynamic protein complexes, which are built of multiple domains that are tethered together by intrinsically disordered polypeptide segments. Examples range from cell signaling to protein sorting and trafficking. Despite their importance in molecular biology, there is currently no single method which can provide information on the overall structure of such protein systems: They are not directly accessible to X-ray crystallography due to the presence of the intrinsically disordered regions (although the folded domains can be crystallized individually). They are also not accessible to NMR techniques due to their large molecular weights. In addition, their inherent flexibility make them practically inaccessible to cryoEM. Notable examples, with great potential applications in biofuel production, are cellulosomes. They are complex multi-enzyme machineries which efficiently degrade plant cell-wall polysaccharides. While many of their individual domains have been characterized structurally by crystallography and NMR methods, the overall conformations of cellulosomal components have been studied by low-resolution methods, including small angle X-ray scattering (SAXS). A number of SAXS experiments exploring the solution structures of the cellulosomal proteins have evidenced that the intrinsically disordered linkers provide conformational flexibility which gives rise to the spatial liberty of the individual globular domains. But the static X-ray scattering methods only indirectly give access to information about conformational flexibility. We combine molecular simulations with SAXS experiments to extract additional, dynamic properties of these proteins. Using this approach, we gain information not only about the distributions of shapes and dimensions of these proteins, but also about such quantities as the probabilities of inter-domain contacts and the end-to-end distance distributions for the flexible linkers. Our results thus provide detailed pictures of the conformational ensembles of the cellulosomal proteins.

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