Crystals of Rous Sarcoma Virus Capsid Protein Show a Helical Arrangement of Protein Subunits

Crystals of Rous sarcoma virus (RSV) capsid protein diffract X rays to 3.5 Å resolution and belong to the monoclinic space groupC2 with unit cell parametersa= 374.4 Å,b= 128.1 Å,c= 200.2 Å, and β = 121.8°. One asymmetric unit of the crystal may contain between 28 and 35 molecules, based on reasonable crystal density assumptions. A self-rotation function and Patterson synthesis suggest that RSV capsid protein crystallizes as a helical array. The determinants of the viral particle morphology are not encoded in the capsid alone. The assembly of a helical array in the crystal reflects the absence of any conformational switching. However, it is expected that the subunit interactions seen in the crystal will be preferred and will relate to those found in the immature or mature virion.