Large-scale
conformational transitions in multi-domain proteins
are often essential for their functions. To investigate the transitions,
it is necessary to explore multiple potential pathways, which involve
different intermediate structures. Here, we present a multi-basin
(MB) coarse-grained (CG) structure-based Go̅ model for describing
transitions in proteins with more than two moving domains. This model
is an extension of our dual-basin Go̅ model in which system-dependent
parameters are determined systematically using the multistate Bennett
acceptance ratio method. In the MB Go̅ model for multi-domain
proteins, we assume that intermediate structures may have partial
inter-domain native contacts. This approach allows us to search multiple
transition pathways that involve distinct intermediate structures
using the CG molecular dynamics (MD) simulations. We apply this scheme
to an enzyme, adenylate kinase (AdK), which has three major domains
and can move along two different pathways. Using the optimized mixing
parameters for each pathway, AdK shows frequent transitions between
the Open, Closed, and the intermediate basins and samples a wide variety
of conformations within each basin. The explored multiple transition
pathways could be compared with experimental data and examined in
more detail by atomistic MD simulations.