The elucidation of assembly pathways of multi-subunit protein complexes is a problem of great interest in structural biology and biomolecular modeling. In this study, we use a new computer algorithm for the simulation of large-scale motion in proteins to dock the subunit PsaC onto Photosystem I. We find that a complicated docking pathway involving multiple conformational changes can be quickly simulated by actively targeting only a few residues at a time to their target positions. Simulations for two possible docking scenarios are explored, and experimental approaches to distinguish between them are discussed.