Crystallization and preliminary X-ray crystallographic analysis of the trimer core from measles virus fusion protein

Two heptad-repeat regions (HR1 and HR2) are highly conserved in paramyxovirus fusion proteins and form a stable helical trimer of heterodimers [(HR1-HR2)(3)] after the fusion between viral and cellular membranes. In this study, two HR regions of the fusion protein of measles virus, a member of the paramyxoviruses, were selected and overexpressed as a single chain (named 2-Helix) connected by an amino-acid linker using a GST-fusion expression system in Escherichia coli. Crystals of 2-Helix protein (GST removed) could be obtained from many conditions using the sitting- or hanging-drop vapour-diffusion method. A complete data set was collected in-house to 1.9 A resolution from a single crystal. The crystal belongs to space group P6, with unit-cell parameters a = b = 51.637, c = 67.058 A. To facilitate the crystal structure solution, SeMet-substituted 2-Helix crystals, grown under similar conditions to the native, were also obtained and diffracted X-rays to 1.8 A using synchrotron radiation.