Structure, Adsorption to Host, and Infection Mechanism of Virulent Lactococcal Phage p2

Abstract

g Lactococcal siphophages from the 936 and P335 groups infect the Gram-positive bacterium Lactococcus lactis using receptor binding proteins (RBPs) attached to their baseplate, a large multiprotein complex at the distal part of the tail. We have previously reported the crystal and electron microscopy (EM) structures of the baseplates of phages p2 (936 group) and TP901-1 (P335 group) as well as the full EM structure of the TP901-1 virion. Here, we report the complete EM structure of siphophage p2, including its capsid, connector complex, tail, and baseplate. Furthermore, we show that the p2 tail is characterized by the presence of protruding decorations, which are related to adhesins and are likely contributed by the major tail protein C-terminal domains. This feature is reminiscent of the tail of Escherichia coli phage and Bacillus subtilis phage SPP1 and might point to a common mechanism for establishing initial interactions with their bacterial hosts. Comparative analyses showed that the architecture of the phage p2 baseplate differs largely from that of lactococcal phage TP901-1. We quantified the interaction of its RBP with the saccharidic receptor and determined that specificity is due to lower k off values of the RBP/saccharidic dissociation. Taken together, these results suggest that the infection of L. lactis strains by phage p2 is a multistep process that involves reversible attachment, followed by baseplate activation, specific attachment of the RBPs to the saccharidic receptor, and DNA ejection.

Cryo-Electron Microscopy Structure of Lactococcal Siphophage 1358 Virion

“…5E). Decorations also have been identified in the tail of other phages, e.g., SPP1 (51), (57), Araucaria (41), and p2 (19). They have been postulated to participate in nonspecific and reversible adhesion of the phage to its host surface polysaccharides, as is the case for the capsid decorations.…”

“…On the other hand, lactococcal siphophages of the P335 group do not go through such BP activation processes (7,17). Lastly, the complete electron microscopy (EM) structure of phage p2 (19) and phage TP901-1 (3) were newly reported.…”

Lactococcal 949 Group Phages Recognize a Carbohydrate Receptor on the Host Cell Surface

“…In order to understand the phage-host interactions of the 949 phages, a focused bioinformatic analysis of the genomic regions that are proposed to encode the so-called "initiator complex" (which in the lactococcal P335 and 936 model systems is comprised of the tail tape measure protein [TMP], the distal tail [Dit] protein, and the tail-associated lysin [Tal] protein [4,32,33]) and the tail tip or so-called "baseplate" regions of the phages, which are proposed to interact with the cell surface receptor (2, 3, 7, 11, 34-36), was undertaken using WRP3 as the model for the species. Based on HHPred analysis, and in keeping with the conserved gene order in other lactococcal phages, e.g., TP901-1 (P335 species) and p2 (936 species), the TMP (predicted to be encoded by orf154 WRP3 ) is recognizable by containing a C-terminal LysM motif, proposed to be involved in peptidoglycan binding and degradation, and two predicted transmembrane domains in the central region of the protein.…”

“…Lactococcal phages are currently classified into 10 species or groups, based on DNA hybridization studies and morphology (1). In recent years, lactococcal phages and their hosts have become an advanced model system for studying Gram-positive phage-host interactions due to the emergence of significant data regarding key molecular players involved in phage adsorption (the phage-encoded receptor binding protein [RBP] and the host-encoded receptor) to the host and the impact of phage infection on sensitive bacterial strains (2)(3)(4)(5)(6)(7)(8)(9)(10)(11). The majority of studies have focused on members of the 936 and P335 species, since these are among the most frequently isolated species in the dairy industry.…”

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.…”