gEMfitter is a program for multiresolution fitting of macromolecular structures. Its main purpose is to fit high resolution protein structures into a low resolution cryo-EM density map. In order to accelerate the expensive 3D correlation calculations, gEMfitter uses multiple processors and multiple threads in parallel in order to use all of the CPU cores and GPUs that are available. gEMfitter can run on a single workstation or a multi-node cluster.

gEMfitter supports several different types of correlation calculation (with or without a Laplacian pre-filter) with a user-defined grid size, and it can perform off-grid optimisation using Powell minimisation. In a recent comparison with the well-known COLORES program (please see References), we showed that gEMfitter gives comparable results to COLORES while being up to three orders of magnitude faster.

The image on the right shows an example of fitting high resolution protein structures into a low resoloution cryo-EM density map of the GroEL–GroES complex (EMD code 1046).