title: The opening of the SPP1 bacteriophage tail, a prevalent mechanism in Gram-positive-infecting siphophages.
abstract: The SPP1 siphophage uses its long non-contractile tail and tail tip to recognize and infect the Gram-positive bacterium Bacillus subtilis. The tail-end cap and its attached tip are the critical components for host recognition and opening of the tail tube for genome exit. In the present work, we determined the cryo-electron microscopic (cryo-EM) structure of a complex formed by the cap protein gp19.1 (Dit) and the N terminus of the downstream protein of gp19.1 in the SPP1 genome, gp21(1-552) (Tal). This complex assembles two back-to-back stacked gp19.1 ring hexamers, interacting loosely, and two gp21(1-552) trimers interacting with gp19.1 at both ends of the stack. Remarkably, one gp21(1-552) trimer displays a "closed" conformation, whereas the second is "open" delineating a central channel. The two conformational states dock nicely into the EM map of the SPP1 cap domain, respectively, before and after DNA release. Moreover, the open/closed conformations of gp19.1-gp21(1-552) are consistent with the structures of the corresponding proteins in the siphophage p2 baseplate, where the Tal protein (ORF16) attached to the ring of Dit (ORF15) was also found to adopt these two conformations. Therefore, the present contribution allowed us to revisit the SPP1 tail distal-end architectural organization. Considering the sequence conservation among Dit and the N-terminal region of Tal-like proteins in Gram-positive-infecting Siphoviridae, it also reveals the Tal opening mechanism as a hallmark of siphophages probably involved in the generation of the firing signal initiating the cascade of events that lead to phage DNA release in vivo.
authors.affiliation: Centre de Biochimie Structurale, INSERM UMR 1054/CNRS UMR 5048 and Universités Montpellier I & II, 29 rue de Navacelles, Montpellier 34090, France.
authors.forename: Adeline
authors.initials: A
authors.lastname: Goulet
authors.forename: Joséphine
authors.initials: J
authors.lastname: Lai-Kee-Him
authors.forename: David
authors.initials: D
authors.lastname: Veesler
authors.forename: Isabelle
authors.initials: I
authors.lastname: Auzat
authors.forename: Gautier
authors.initials: G
authors.lastname: Robin
authors.forename: Dale A
authors.initials: DA
authors.lastname: Shepherd
authors.forename: Alison E
authors.initials: AE
authors.lastname: Ashcroft
authors.forename: Eric
authors.initials: E
authors.lastname: Richard
authors.forename: Julie
authors.initials: J
authors.lastname: Lichière
authors.forename: Paulo
authors.initials: P
authors.lastname: Tavares
authors.forename: Christian
authors.initials: C
authors.lastname: Cambillau
authors.forename: Patrick
authors.initials: P
authors.lastname: Bron
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure / Q000821:virology*; D016679:Genome, Viral / Q000502:physiology*; D017434:Protein Structure, Tertiary; D017906:Siphoviridae / Q000502:physiology* / Q000648:ultrastructure; D015678:Viral Structural Proteins / Q000235:genetics / Q000378:metabolism*; D053585:Virus Attachment
chemical_list: D015678:Viral Structural Proteins