Accurate sampling of conformational space and, in particular, the
transitions between functional substates has been a challenge in molecular
dynamic (MD) simulations of large biomolecular systems. We developed an Elastic
Network Model (ENM)-based computational method, ClustENM, for sampling large
conformational changes of biomolecules with various sizes and oligomerization
states. ClustENM is an iterative method that combines ENM with energy
minimization and clustering steps. It is an unbiased technique, which requires
only an initial structure as input, and no information about the target
conformation. To test the performance of ClustENM, we applied it to six
biomolecular systems: adenylate kinase (AK), calmodulin, p38 MAP kinase, HIV-1
reverse transcriptase (RT), triosephosphate isomerase (TIM), and the 70S
ribosomal complex. The generated ensembles of conformers determined at atomic
resolution show good agreement with experimental data (979 structures resolved
by X-ray and/or NMR) and encompass the subspaces covered in independent MD
simulations for TIM, p38, and RT. ClustENM emerges as a computationally
efficient tool for characterizing the conformational space of large systems at
atomic detail, in addition to generating a representative ensemble of conformers
that can be advantageously used in simulating substrate/ligand-binding
events.