title: Baseplate assembly of phage Mu: Defining the conserved core components of contractile-tailed phages and related bacterial systems.
abstract: Contractile phage tails are powerful cell puncturing nanomachines that have been co-opted by bacteria for self-defense against both bacteria and eukaryotic cells. The tail of phage T4 has long served as the paradigm for understanding contractile tail-like systems despite its greater complexity compared with other contractile-tailed phages. Here, we present a detailed investigation of the assembly of a "simple" contractile-tailed phage baseplate, that of Escherichia coli phage Mu. By coexpressing various combinations of putative Mu baseplate proteins, we defined the required components of this baseplate and delineated its assembly pathway. We show that the Mu baseplate is constructed through the independent assembly of wedges that are organized around a central hub complex. The Mu wedges are comprised of only three protein subunits rather than the seven found in the equivalent structure in T4. Through extensive bioinformatic analyses, we found that homologs of the essential components of the Mu baseplate can be identified in the majority of contractile-tailed phages and prophages. No T4-like prophages were identified. The conserved simple baseplate components were also found in contractile tail-derived bacterial apparatuses, such as type VI secretion systems, Photorhabdus virulence cassettes, and R-type tailocins. Our work highlights the evolutionary connections and similarities in the biochemical behavior of phage Mu wedge components and the TssF and TssG proteins of the type VI secretion system. In addition, we demonstrate the importance of the Mu baseplate as a model system for understanding bacterial phage tail-derived systems.
authors.affiliation: Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada;
authors.forename: Carina R
authors.initials: CR
authors.lastname: Büttner
authors.affiliation: Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada; Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Computer Science, University of Toronto, Toronto, ON M5S 3G4, Canada;
authors.forename: Yingzhou
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada karen.maxwell@utoronto.ca alan.davidson@utoronto.ca.
authors.forename: Karen L
authors.initials: KL
authors.lastname: Maxwell
authors.affiliation: Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada karen.maxwell@utoronto.ca alan.davidson@utoronto.ca.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Davidson
mesh_terms: D001412:Bacillus subtilis / Q000821:virology; D017901:Bacteriophage P2 / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D017122:Bacteriophage T4 / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D010583:Bacteriophage mu / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D019295:Computational Biology; D004926:Escherichia coli / Q000821:virology; D015870:Gene Expression; D026801:Synteny; D000069376:Type VI Secretion Systems / Q000235:genetics* / Q000378:metabolism; D017376:Viral Tail Proteins / Q000235:genetics* / Q000378:metabolism; D014771:Virion / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D019065:Virus Assembly / Q000235:genetics*
chemical_list: D000069376:Type VI Secretion Systems; D017376:Viral Tail Proteins
keywords: assembly; baseplate; contractile tail; phage Mu