Assembly of bacteriophage PRD1 spike complex: Role of the multidomain protein P5

The spike structure of bacteriophage PRDL is comprised of proteins P2, P5, and P31. It resembles the corresponding receptor-binding structure of adeno viruses. We show that purified recombinant protein P5 is an elongated (30 x 2.7 nm; R-h = 5.5 nm), multidomain trimer which can slowly associate into nonamers. Cleavage of thr 340 amino acid long P5 with collagenase yields 2 fragments. The larger, 205 amino acid long C-terminal fragment appears to c ontain the residues responsible for the trimerization of the protein, where as the smaller N-terminal part mediates the interaction of P5 with the pent americ vertex protein P31 (24 x 2.5 nm, R-h = 4.2 nm), In addition, the pre sence of the N-terminal sequence is required for the formation of the P5 no namer. 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 ads orption protein P2 (21 x 2.5 nm; R-h = 4.1 nm). Our results also suggest th at the P5 trimer forms a substantial part of the viral spike shaft that was previously thought to be composed exclusively of protein P2.