Flexible image registration for the identification of best fitted protein models in 3D-EM maps

In this work we propose an image registration algorithm to automatically fit protein atomic domain models into medium-resolution three-dimensional electron microscopy reconstructions (3D-EM map). The approach employs a flexible registration algorithm whose optimizer controls the generation of stereo-chemically correct models from a given reference domain belonging to a super-family of proteins. The proposed algorithm generates models automatically in the correct direction until the optimizer converges to the best fitted model. A local gradient optimizer is employed for this task. Mutual Information is used as an alternative to Cross Correlation Coefficient. An additional rigid registration that uses a local gradient optimization is applied between each generated model and the 3D-EM map.