Assembly of Bacteriophage PRD1 Spike Complex: Role of the Multidomain Protein P5

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Abstract
The spike structure of bacteriophage PRD1 is comprised of proteins P2, P5, and P31. It resembles the corresponding receptor-binding structure of adenoviruses. We show that purified recombinant protein P5 is an elongated (30 × 2.7 nm; Rh = 5.5 nm), multidomain trimer which can slowly associate into nonamers. Cleavage of the 340 amino acid long P5 with collagenase yields 2 fragments. The larger, 205 amino acid long C-terminal fragment appears to contain the residues responsible for the trimerization of the protein, whereas the smaller N-terminal part mediates the interaction of P5 with the pentameric vertex protein P31 (24 × 2.5 nm, Rh = 4.2 nm). In addition, the presence of the N-terminal sequence is required for the formation of the P5 nonamer. The results presented here suggest that P5 and P31 form an elongated adaptor complex at the 5-fold vertexes of the virion which anchors the adsorption protein P2 (21 × 2.5 nm; Rh = 4.1 nm). Our results also suggest that the P5 trimer forms a substantial part of the viral spike shaft that was previously thought to be composed exclusively of protein P2.