The Atomic Structure of the Phage Tuc2009 Baseplate Tripod Suggests that Host Recognition Involves Two Different Carbohydrate Binding Modules

Abstract

The Gram-positive bacterium Lactococcus lactis, used for the production of cheeses and other fermented dairy products, falls victim frequently to fortuitous infection by tailed phages. The accompanying risk of dairy fermentation failures in industrial facilities has prompted in-depth investigations of these phages. Lactococcal phage Tuc2009 possesses extensive genomic homology to phage TP901-1. However, striking differences in the baseplate-encoding genes stimulated our interest in solving the structure of this host’s adhesion device. We report here the X-ray structures of phage Tuc2009 receptor binding protein (RBP) and of a “tripod” assembly of three baseplate components, BppU, BppA, and BppL (the RBP). These structures made it possible to generate a realistic atomic model of the complete Tuc2009 baseplate that consists of an 84-protein complex: 18 BppU, 12 BppA, and 54 BppL proteins. The RBP head domain possesses a different fold than those of phages p2, TP901-1, and 1358, while the so-called “stem” and “neck” domains share structural features with their equivalents in phage TP901-1. The BppA module interacts strongly with the BppU N-terminal domain. Unlike other characterized lactococcal phages, Tuc2009 baseplate harbors two different carbohydrate recognition sites: one in the bona fide RBP head domain and the other in BppA. These findings represent a major step forward in deciphering the molecular mechanism by which Tuc2009 recognizes its saccharidic receptor(s) on its host.

The Presence of Two Receptor-Binding Proteins Contributes to the Wide Host Range of Staphylococcal Twort-Like Phages

“…Two different RBPs, LtfA and LtfB of the T5-like siphoviruses DT57C and DT571/2, recognize different O antigens, i.e., the O22 or O87 type and the O81 type, respectively (55). Two different carbohydrate-binding modules have been identified in Lactococcus lactis phage Tuc2009; the first is in a classical bona fide RBP (BppL), and the other is in an accessory protein, BppA (56). BppA enhances adsorption to cells, although its true contribution is not fully understood (57).…”

Structure of the host-recognition device of Staphylococcus aureus phage ϕ11

“…In contrast, ϕ11 Gp45, the RBP, does not exhibit analogy with other phage RBPs, in particular with those from lactococcal phages that also bind to saccharidic receptors. Lactococcal phages p2 52, TP901-1 53, Tuc2009 19, bIL170 54 and 1358 4 all possess a trimeric receptor recognition head sharing a bona fide or a modified jelly-roll motif. The rest of their RBPs share common motifs in the neck or in the N-terminal domain (or stem).…”

Genetic determinants of lactococcal C2viruses for host infection and their role in phage evolution

“…HHpred analyses of gpl14/gp34 from all phages in this study result in top domain hit 5E7T (5e7t_B); minor structural protein 5; bacteriophages; Lactococcus lactis. Minor structural protein 5 is identified as ORF 52/BppA in lactococcal phage TUC2009 (accession number NC_002703), a component of the tripod baseplate structure with a putative carbohydrate binding domain and involved in receptor binding (McGrath et al , 2006, Legrand et al , 2016). gpl16/gp36 are classified as minor structural/hypothetical proteins (NP_043564/NP_042309), possibly collar proteins as a gene with 76 % identity to ORF36 was found in addition to l16 in a phage c2 isolate exhibiting a prominent collar structure at its head–tail interface (accession number AAD20610).…”

“…Although our results show a clear relationship between gpl14–15–16 and gp34–35–36, with their corresponding YueB orthologues Pip and YjaE, respectively, structural domain analysis does not predict direct protein interaction. Rather gpl14–15–16 and gp34–35–36 are more similar to Tuc2009 BppA Tuc2009 for which the exact function in host adsorption is yet to be fully elucidated (Legrand et al , 2016). …”