Crystallization and Preliminary X-Ray Analysis of Receptor-Binding Protein P2 of Bacteriophage PRD1

BacteriophagePRD1 has remarkable structural similarities to adenovirus, but is unusual in containing a membrane beneath its icosahedral capsid. Its monomeric receptor-binding protein, P2, is part of a complex at each capsid vertex and so is the functional equivalent of adenovirus fiber. P2 has been crystallized by the “hanging-drop” method of vapor diffusion and two different crystal forms were obtained. Macroseeding, used to increase the size of the initial small needles, gave rod-shaped crystals. These grew to a size of 0.08 × 0.08 × 0.50 mm3 and diffracted to 2.6 Å resolution. They have the orthorhombic space group P2221, with unit cell dimensions a = 137.8 Å, b = 46.5 Å, c = 136.4 Å. A few single crystals of a second form were grown without seeding under slightly different conditions. A parallelepiped crystal (0.10 × 0.10 × 0.35 mm3), with space group C2221 and unit cell dimensions a = 182.3 Å, b = 204.8 Å, c = 133.3 Å, diffracted to 3.5 Å resolution. A rotation function for the second form revealed that four monomers of P2 are related by a noncrystallographic twofold axis. The structure of P2 will reveal how this arrangement relates to the trimeric adenovirus fiber.