Diffraction data were integrated by XDS (77) and scaled with AIMLESS (78). Phases were obtained by molecular replacement using the crystal structure of MeV wt P MD (PDB code 3ZDO) (19) using MOLREP (79). Data analysis by the STARANISO server (http://staraniso.globalphasing.org/cgi-bin/staraniso.cgi) revealed an anisotropic diffraction with resolution limits of 2.5 Å along the a* and b* axes and 1.9 Å on the c* axis. To take into account this anisotropy, an ellipsoidal resolution limit mask was used and rescaling was performed by STARANISO. Model building was manually done with COOT (80), and refinement was performed using BUSTER (81) and REFMAC (82). PyMOL (PyMOL Molecular Graphics System, version 2.0, Schrödinger, LLC) was used to visualize and draw the models. The quality of the final model was evaluated using MolProbity (http://molprobity.biochem.duke.edu/). The server PDBeFold from EMBL-EBI (http://www.ebi.ac.uk/msd-srv/ssm/ssmstart.html) was used to compute root mean square deviations (RMSDs) between P MD structures. Coiled-coil analysis was carried out using TWISTER (83).