Discovery of protein substructures in EM maps

Cryo-EM has became an increasingly powerful technique for elucidating the structure, dynamics and function of large flexible macromolecule assemblies that cannot be determined at atomic-resolution. A major challenge in analyzing EM maps of complexes is the identification of their subnnits. We propose a fully automated highly efficient method for discovering high-resolution subunits of a complex, given an nu intermediate resolution map, without prior knowledge of their bomuhiries and content. The method extracts helices from an EM map and uses their spatial arrangement to detect candidate subunits. The method was tested successfully on several simulated 8.0Å resolution maps. Tho obtained spatial helix arrangement was sufficient for the discovery of the correct subunits from a dataset of 887 SCOP representativtes.