Solution structure of bacteriophage PRD1 vertex complex

Bacteriophage PRD1 is a prototype of viruses with an internal membrane. The icosahedral capsid and major coat protein share structural similarity with the corresponding structures of adenovirus. The present study further expl ores similarities between these viruses, considering the 5-fold vertex asse mblies. The vertex structure of bacteriophage PRD1 consists of proteins P2, P5, and P31. The vertex complex mediates host cell binding and controls do uble-stranded DNA delivery. Quaternary structures and interactions of purif ied spike proteins were studied by synchrotron radiation x-ray solution sca ttering. Low resolution models of the vertex proteins P5, P2, and P31 were reconstructed ab initio from the scattering data. Protein P5 is a long trim er that resembles the adenovirus spike protein pIV. The receptor-binding pr otein P2 is a 15.5-nm long, thin monomer and does not have an adenovirus co unterpart. P31 forms a pentameric base with a maximum diameter of 8.5 nm, w hich is thinner than the adenovirus penton pIII P5 further polymerize into a nonameric form ((p5(3))(3)). In the presence of P31, P5 associates into a P5(6):P31 complex. The constructed models of these assemblies provided sup port for a model of vertex assembly onto the virion. Although similar in ov erall architecture, clear differences between PRD1 and adenovirus spike ass emblies have been revealed.