Crystallization and preliminary crystallographic analysis of the heptad-repeat complex of SARS coronavirus spike protein.

The aetiological agent of an emergent outbreak of atypical pneumonia, severe acute respiratory syndrome (SARS), is a positive-stranded RNA virus (SARS-CoV) belonging to the Coronaviridae family with a genome that differs substantially from those of other known coronaviruses. Highly conserved heptad-repeat (HR1 and HR2) regions in class I viral fusion proteins, including spike protein from SARS coronavirus, interact with each other to form a six-helix bundle, which is called a fusion core. The crystal structure of the fusion core is expected to greatly facilitate drug design. Crystals of the fusion core of SARS-CoV spike protein have been grown at 291 K using PEG 4000 as precipitant. The diffraction pattern of the crystal extends to 2.8 A resolution at 100 K in-house. The crystals have unit-cell parameters a = 121.2, b = 66.3, c = 70.0 A, alpha = gamma = 90, beta = 107.4 degrees and belong to space group C2. Assuming the presence of six molecules per asymmetric unit, the solvent content is estimated to be about 28%.