title: 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.
  
  
  OBJECTIVE
  Understanding how siphophages infect Lactococcus lactis is of commercial importance as they cause milk fermentation failures in the dairy industry. In addition, such knowledge is crucial in a general sense in order to understand how viruses recognize their host through protein-glycan interactions. We report here the lactococcal phage Tuc2009 receptor binding protein (RBP) structure as well as that of its baseplate. The RBP head domain has a different fold than those of phages p2, TP901-1, and 1358, while the so-called "stem" and "neck" share the fold characteristics also found in the equivalent baseplate proteins of phage TP901-1. The baseplate structure contains, in contrast to other characterized lactococcal phages, two different carbohydrate binding modules that may bind different motifs of the host's surface polysaccharide.
authors.affiliation: Synchrotron Soleil, L'Orme des Merisiers, Gif-sur-Yvette, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Legrand
authors.affiliation: School of Microbiology, University College Cork, Cork, Ireland.
authors.forename: Barry
authors.initials: B
authors.lastname: Collins
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Marseille, France Architecture et Fonction des Macromolécules Biologiques, Centre National de la Recherche Scientifique (CNRS), Campus de Luminy, Marseille, France.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Blangy
authors.affiliation: School of Microbiology, University College Cork, Cork, Ireland.
authors.forename: James
authors.initials: J
authors.lastname: Murphy
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Marseille, France Architecture et Fonction des Macromolécules Biologiques, Centre National de la Recherche Scientifique (CNRS), Campus de Luminy, Marseille, France.
authors.forename: Silvia
authors.initials: S
authors.lastname: Spinelli
authors.affiliation: Research Institute of Biomedical and Health Sciences, Universidad de Las Palmas de Gran Canaria (ULPGC), Las Palmas, Canary Islands, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Gutierrez
authors.affiliation: Synchrotron Soleil, L'Orme des Merisiers, Gif-sur-Yvette, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Richet
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Marseille, France Architecture et Fonction des Macromolécules Biologiques, Centre National de la Recherche Scientifique (CNRS), Campus de Luminy, Marseille, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Kellenberger
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Marseille, France Architecture et Fonction des Macromolécules Biologiques, Centre National de la Recherche Scientifique (CNRS), Campus de Luminy, Marseille, France.
authors.forename: Aline
authors.initials: A
authors.lastname: Desmyter
authors.affiliation: School of Microbiology, University College Cork, Cork, Ireland.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Mahony
authors.affiliation: School of Microbiology, University College Cork, Cork, Ireland APC Microbiome Institute, University College Cork, Cork, Ireland d.vansinderen@ucc.ie cambillau@afmb.univ-mrs.fr.
authors.forename: Douwe
authors.initials: D
authors.lastname: van Sinderen
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Campus de Luminy, Marseille, France Architecture et Fonction des Macromolécules Biologiques, Centre National de la Recherche Scientifique (CNRS), Campus de Luminy, Marseille, France d.vansinderen@ucc.ie cambillau@afmb.univ-mrs.fr.
authors.forename: Christian
authors.initials: C
authors.lastname: Cambillau
mesh_terms: D001435:Bacteriophages / Q000737:chemistry*; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D018360:Crystallography, X-Ray; D013294:Lactococcus lactis / Q000821:virology*; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017906:Siphoviridae / Q000737:chemistry; D017376:Viral Tail Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D046912:Multiprotein Complexes; D017376:Viral Tail Proteins
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