Structure of the phage TP901-1 1.8 MDa baseplate suggests an alternative host adhesion mechanism

Abstract

Phages of the Caudovirales order possess a tail that recognizes the host and ensures genome delivery upon infection. The X-ray structure of the approximately 1.8 MDa host adsorption device (baseplate) from the lactococcal phage TP901-1 shows that the receptor-binding proteins are pointing in the direction of the host, suggesting that this organelle is in a conformation ready for host adhesion. This result is in marked contrast with the lactococcal phage p2 situation, whose baseplate is known to undergo huge conformational changes in the presence of Ca 2þ to reach its active state. In vivo infection experiments confirmed these structural observations by demonstrating that Ca 2þ ions are required for host adhesion among p2-like phages (936-species) but have no influence on TP901-1-like phages (P335-species). These data suggest that these two families rely on diverse adhesion strategies which may lead to different signaling for genome release.bacteriophage | crystal structure | Lactococcus lactis | siphoviridae | viral infection B acterial viruses (phages) are elegant nanomachines infecting their hosts with high specificity and efficiency. The vast majority of them belong to the Caudovirales order and possess a tail appendage used to recognize the host and ensure genome delivery. This organelle seems to be responsible for the unequaled efficacy of these virions, as compared to eukaryotic viruses, as each phage particle can infect a target cell (1). The initial events of the infection process have been characterized for a limited number of phages demonstrating that dramatic conformational changes at the distal tail end accompany the DNA injection event (2-7). Binding of myophage T4 to the host lipopolysaccharides induces dramatic rearrangements of its tail extremity allowing irreversible commitment to the target cell followed by puncturing of its surface (3, 5). The emerging picture for Podoviridae is that after attachment to the cell envelope, the minor phage proteins are ejected to form a tube across the periplasm thereby directing the viral DNA into the host cytoplasm (8). Siphophage p2, belonging to the 936-species of lactococcal phages, exhibits a Ca 2þ -mediated activation mechanism inducing a 200°rotation of the receptor-binding proteins (RBPs) to establish multiple interactions with host saccharides and initiate infection (7). Here we report the crystal structure of the baseplate from the lactoccocal phage TP901-1 (P335-species) at 3.8 Å resolution and show that it is in a conformation ready for host adhesion, ruling out the involvement of a Ca 2þ -mediated or any other major conformational changes of this organelle at this initial step. We extended these conclusions by demonstrating that authentic virions can infect their host with maximal efficacy in the absence of added Ca 2þ and that this behavior is conserved among the TP901-1 phage species (P335). We therefore suggest that TP901-1-like phages do not rely on baseplate conformational changes for host adsorption, in contrast to what has been observed for ...

The First Structure of a Mycobacteriophage, the Mycobacterium abscessus subsp. bolletii Phage Araucaria

“…In contrast, lactococcal phages of the 936 and P335 families seem to attach exclusively to polysaccharides and bear at their tail end a large macromolecular entity called the baseplate. The baseplate dimensions of phages p2 and TP901-1 are quite large, since these phages harbor a large number (18 to 54) of receptor binding proteins (RBPs), the specific proteins recognizing and attaching to the host (48,49). These baseplates have been found, to date, to be composed of a central axial core formed by Dit and Tal, shared with the straighttail tip phages (e.g., SPP1), and of a peripheral component formed by the RBPs as in phage p2 (49,71) and eventually other proteins as in phages TP901-1 (48,72) and Tuc2009 (73,74).…”

“…HHpred searches revealed that the ORF protein following the TMP, ORF70, shares with ϳ80% probability structural similarity with the corresponding protein, Dit, in phage SPP1 and lactococcal phage TP901-1. The X-ray structures of Dit from phages SPP1 (gp19.1) (47), TP901-1 (ORF46 protein) (48), and p2 (ORF15 protein) (49) have been reported, and they were found to share close structural similarities. HHpred also predicted that the ORF71 protein shares structural similarity (98% similarity) with a prophage MUSO2 43-kDa tail protein (PDB 3CDD).…”

Molecular architecture of tailed double-stranded DNA phages

“…128,129 The tail tip complex has different size and morphology in different phages. Phages which use protein receptors for cell binding usually have conical tail tips (e.g., SPP1 130 and λ), whereas phages, using polysaccharide receptors usually have elaborate baseplates at the distal end of the tail (e.g., lactococcal phages TP901-1 6,131 and p2 132,133 ). Furthermore phages usually have side tail fibers or spikes, attached to the periphery of the tail tip complex, as well as a central tail spike.…”

“…154 The best studied Siphoviridae baseplates are those of phages p2 and TP901-1 infecting Gram-positive Lactococcus lactis. 131,132 Both these phages use carbohydrate molecules as receptors for attachment to the host. The p2 baseplate (Fig.…”

“…132 The baseplate of the phage TP901-1 contains a hexameric ring of Dit which attaches 6 trimers of the baseplate upper protein (BppU) to its periphery. 131 Each BppU monomer, in turn, attaches a trimer of the receptor binding protein, resulting in 54 copies of the receptor binding subunits per phage. Thus BppU serves as an adaptor between Dit and the receptor-binding protein, allowing TP901-1 to expose 3 times more receptor-binding molecules on its baseplate compared with phage p2.…”