128 / 161
Conformational Ensembles from Experimental Data
and Computer Simulations
Poster Abstracts
124
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.